Nevada Terawatt Facility Annual Report

Nevada Terawatt Facility

Physics Department University of Nevada, Reno Annual Report 2010/2013

JANUARY 29, 2014

DOE # DE-FC52-06NA27616

NEVADA TERAWATT FACILITY

Introduction

University of Nevada, RenoNevada Terawatt Facility

Table of Contents

Title Author Page #

Introduction

Annual Report: 2011-2013 Executive Overview A.M. Covington 6

Scientific Programs

Science by NTF Faculty

CovingtonNegative Ion Photodetachment Studies Through Velocity-map Imaging Spectroscopy

K. Chartkunchand 10

Multi-parameter Characterization of Laser Ablation Plumes J.J. Iratcabal 12Isotope Activation in Zebra Z-pinch Z. McCormick 14Laser-produced Neutrons and Isotopes Z. McCormick 16

DarlingDeuteriding Solids for Zebra and Leopard Targets T. W. Darling 18Developing Experimental Methods to Study the Dynamic Compression of Materials at the Nevada Terawatt Facility

B.D. Hammel 20

Production and Measurement of Fast Neutrons at Zebra E. McKee 22

IvanovCurrent Redistribution and Generation of Kinetic Engery in the Stagnated Z-pinch

V.V. Ivanov 24

Development of UV Laser Dianostics for the Dense Z-pinch V.V. Ivanov 26Study of the Internal Structure and Instabilities in the Dense Z-pinch V.V. Ivanov 28X-Ray Absorption Spectroscopy and Imaging for Wire-array Z-pinches A.A. Anderson 30Investigation of Implosion Dynamics in Nested Cylindrical and Star Wire Arrays

D Papp 32

PresuraDeveloping Zeeman Broadening Diagnostics for Magnetized Plasmas at NTF

S. Haque 34

2D Spatially-resolved Imaging Spectroscopy of Z-pinch Plasmas with Convex Bent Crystals

D. Papp 36

Focusing of an Explosive Plasma Expansion in a Transverse Magnetic Field

R. Presura / C. Plechaty

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Table of Contents

Title Author Page #

Staged Z-pinch Implosions to Produce High-Energy-Density Plasma R. Presura / H. Rahman

40

Kelvin-Helmholtz Instablities Generated in Magnetized High-Energy-Density Plasma

R. Presura / S. Stein 42

Electron Energy Characterization of Electron Beams in Z-Pinch Plasmas Using Magnetic Deflection

M. Wallace 44

SentokuResistive Guiding of Laser-driven Fast Electrons in Solids P. Leblanc 46Higher-order Terms of Radiative Damping in Extreme Intense Laser-matter Interaction

R. Pandit 48

Radiation Transport in Ultrafast Heated High-Z Solid Targets I. Paraschiv 50

Science by Collaborators and Users

Proton Deflectometry for Investigation of Magnetic Field Configuration in Pulsed-power-driven Systems

D Marical / F Beg 52

Experimental Studies of Implosion Characteristics and Radiation Properties of Planar and Cylindrical Wire Arrays and X-pinches

V. Kanstryev 54

Measurements of Electron Beam and Subsequent Characteristic Kα and L-shell emission from Brass Wire-array Implosions

A. Safronroa 56

Unique Spectral Features from Multi-charged Plasmas Irradiated by Relativistic Sub-picosecond Laser Pulses on the Leopard Laser at the UNR/NTF

A. Safronroa 58

Experimental Investigation of Fast-electron Generation Using the Leopard Short-pulse Laser

H. Sawada 60

Results of Experiments with Mixed Nested Wires Arrays and Silver Planar Wire Arrays on Zebra with an Application to Lasing

M. Weller 62

Plasma Formation and Evolution from a Copper Surface Driven by a Mega-ampere Current Pulse

K. Yates 64

Facilities

Mechanical Engineering and Support of Experiments at the NTF A. Astanovitskiy 67NTF Operations and Maintenance V. Davis 69Electrical Engineering and Experimental Support on the 1 MA Zebra Z-pinch Machine and the 50 TW Leopard Laser System

V. Nalajala 71

Leopard II Laser Development P. Wiewior 73


Table of Contents

Title Author Page #

Publications & Presentations

2013 762012 842011 93

Staffing

NTF Employee listing 102

StatisticsNTF Funding Allocation 104NTF Staffing & GRAs 105NTF Shot Activity 106Publications 107UNR Degrees in HEDP 05-13 108UNR Degrees Granted in Physics 109UNR Degrees Granted - Masters & Ph.Ds 109

Nevada Terawatt Facility Annual Report: 2011-2013 Overview

Aaron Covington, Interim Director

Nevada Terawatt Facility, Department of Physics, University of Nevada, Reno

Over the past three years, the Nevada

Terawatt Facility (NTF) has carried out a vigorous academic research program in high energy density plasma (HEDP) physics as part of the NNSA’s Stewardship Science Academic Alliance. NTF experimental capabilities are based on TW-class Z-pinch generator and laser experiments that enable scientific exploration and discovery across a broad range of plasma regimes. The effective utilization of these unique university-based facilities has allowed us to conduct world-class science while achieving our primary mission- that of training and cultivating the next generation of outstanding HEDP research scientists.

This report gives an overview of NTF scientific, technical and student achievements since the last review in October of 2010. Contributed articles follow giving brief summaries of NTF R&D activities supported in whole or in part by the Cooperative Agreement with NNSA. Despite a drastic reduction in core funding provided to the facility, the NTF continues to implement an innovative and robust scientific portfolio that has expanded to include several competitively funded individual efforts. Scientific Achievements

Since the last review, the NTF has continued to display leadership in fundamental plasma science and diagnostic development. Over 60 articles have been published in peer-reviewed journals, invited papers and conference proceedings. These articles include a number of pioneering efforts that have been published in prestigious journals such as Physical Review Letters and Nature. The exceptionally high productivity of UNR Physics Department efforts have led to a top rating among HEDP institutions worldwide [Elsevier, 2013] with the

vast majority of experiments being conducted at the NTF. Our science has also been disseminated to the HEDP community at large through more than 100 talks and poster presentations over the past three years.

It should be noted that in response to comments from past program reviewers, the NTF has also undertaken an intensive effort to attract more competitive funding. Hence, in the past three years, over 33 grant proposals have been submitted (12 are pending) that use NTF experimental or computational capability. Of these, four have been awarded, demonstrating the competitiveness of our program.

A brief list of noteworthy NTF HEDP efforts undertaken during the program review period includes:

• Proton deflectometry investigations of

magnetic field structures in pulsed-power systems.

• Continuous improvements in UV shadowgraphy and interferometry of pinched plasmas w/ ~micron resolution

• X-ray absorption spectroscopy and imaging of Z-pinch plasmas- experiment and theory

• Measurements of dynamic magnetic field strengths via Zeeman spectroscopy

• Implosion dynamics, radiative properties and opacity effects of wire arrays with open and closed magnetic configurations

• Star wire arrays used to produce two-component Z-pinch plasma

• Measurements of plasma polarization • Plasma penetration across magnetic fields • Sheared flow stabilization using conical

arrays • Studies of magnetically accelerated flyer

plates • Jet-induced shock formation in materials

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• Fundamental studies of plasma instability seeding, evolution and mitigation

• Increased HED target materials fabrication and quality control

• Continued development of collisional PIC-codes to solid density w/ integration of radiation transport

• Continued studies of non-linear fluid instabilities including temperature gradients and temperature fluctuations

Operations/Facility Improvements

A thorough overhaul of all aspects of NTF operations has been implemented over the past three years to increase productivity and the efficiency and reliability of NTF experimental systems. Experimental calls for proposals have been streamlined and users are required to participate in a more formal campaign planning & execution process. Maintenance, lifecycle management, SOPs, shot and safety protocols have also been updated. We have also identified mission critical end items and where possible have attempted to make sure spares are on hand in case a long lead-time part fails. Administrative policies have been implemented to clarify expectations of employees in a number of areas including property accountability and inventory control. The NTF management team has also worked with UNR to create mechanisms that allow individual users to access the NTF and reimburse costs to the Cooperative Agreement as required by NNSA.

Numerous facility and equipment upgrades have also been completed. The most important of these is realization of the fully operational Leopard II Laser that operates reliably and within user required specifications. Leopard II is delivering short-pulse laser light on target with improved contrast and acceptable jitter. When coupled with Zebra Z-pinch, Leopard II has increased the regions of HED phase space that are experimentally accessible at the NTF. Successful short- and long-pulse campaigns have been carried out with much higher energy on target. The NTF is routinely conducting experiments that synchronize the Z-pinch with Leopard laser and coupled campaigns now account for ~30% of total shot allocation time.

Other upgrades include SAGE building infrastructure and support equipment. Building upgrades include a new elevator, emergency generator, expanded electrical capacity and a new HVAC system. A CNC Milling machine was procured with help from the Physics Department to aid in the mechanical fabrication of complex parts and a new welding area has been constructed. We have also redesigned and installed cooling recirculation and water treatment systems on Zebra.

The NTF is also fielding enhanced diagnostics on each Zebra and Leopard shots. This is allowing us to obtain higher scientific value from each shot. We have installed a time-gated X-ray streak camera and have partnered with NSTeC to field a new white-light streak camera system. Dr. Ivanov has also led an effort to upgrade the abandoned NTF Tomcat Laser to allow for deep UV shadowgraphy and interferometry. Other experimental systems are also online including neutron detectors (w/ MCNP modeling support) and activation counting systems.

Another important facility improvement was the dedication of renovated spaces as Student Discovery Science Labs. These areas now include the Materials and Target Fabrication Lab, in which students can use evaporators and heat treatment systems to design and construct unique HED targets. Moreover, a small Pulsed Power Development Lab is currently up and running that allows students to test ideas on a small 100kV “pulser” system that can be scaled to Zebra. An Optical Diagnostics and Calibration Lab is also available where laser produced plasmas can be used to test and calibrate diagnostics.

A list of NTF shot statistics and

operational capabilities includes: • From CY 2011-2013, a total of 938 shots

were completed on Zebra including 110 coupled shots

• Computational efforts are bolstered by two Linux cluster systems, totaling 86 nodes with 18.6 TBytes of RAM.

• Lower-jitter coupling of short pulse (τ = 350 fs) Leopard light with Zebra

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• Demonstration of new versions of Load Current Multiplier (LCM) on Zebra w/ currents near 2 MA

• We have achieved synchronization (±8 ns optimal, ±25 ns nominal) between Zebra and Leopard with electrical triggering with the gas switch

• Optimization of adaptive optics: improved focal spot on target and shot rate

• Shot-by-shot characterization of the laser: far-field, near-field, energy, spectral bandwidth, contrast ratio and pulse duration for each pulse

• New regimes for experiments: a long pulse regime (1ns)

• Stronger ties with UNR Environmental Health & Safety and Facilities

• More formality in safety training • Design and installation of an engineered

safety system- reduced dependence on administrative safety controls

• The upgraded Cheetah Laser was fully commissioned last January with financial support being provided by UNR.

Student Achievements

The most important measure of our program is found in the success of our students following graduation from the UNR Physics Department. Since the time of the last review, 19 students concentrating in HED Physics have earned doctorates from our graduate program (see Appendix Table 1). Of these, five have gone on to post-doctoral appointments at NNSA or DoD laboratories in defense science. In the same time period, four of our former graduates have accepted technical staff member positions at NNSA or DoD labs. As is evident from Table 1, a vast majority of our graduates have found employment in government and university labs or in industry.

A brief list highlighting NTF student

achievements since the last review includes:

• Student-led experiments now account for a majority of NTF campaigns

• New student research & employment opportunities via collaborations with industry/government lab scientists & engineers (NSTeC & LLNL)

• Exceptional UNR/NTF degree production at all levels w/ skills in HEDP science

• NTF is now a laboratory astrophysics experiment platform for University of Toledo astronomy and physics REU students

• Former students are finding positions throughout the HEDP community and beyond

Outreach & Recruiting

Owing to funding limitations and uncertainties, we have suspended all NTF recruiting activities. Following up on a verbal directive from NNSA HQ, we are not using NNSA Cooperative Agreement funds to replace vacancies created as doctoral students graduate, although some new students have been hired into positions by PIs of individual grants that use the NTF. Formal graduate student recruitment will be restarted if more secure funding sources are located in the near future. We are actively recruiting undergraduate students to undertake shorter-term (~1 year) Senior Thesis Projects using the facility.

The NTF is also continuing to participate in a variety of outreach activities with local area schools, civic groups and businesses. We usually give tours of the facility to several gifted & talented student groups each year. Some of these efforts have created opportunities for students from local area high schools to work on NTF-supported research projects. We have also started working with local area companies interested in a variety of university-industry projects that have parallel interests to the facility (Firebird Sensors- Laser Power Sensors, Positive ID Corp- Development of radiation bio-sensors, etc.). Acknowledgements

We are grateful for the dedicated efforts of Ms. Geraldine Ferguson and Ms. Phyllis Schmidt and for consistent support from the UNR Department of Physics and College of Science. NTF efforts were supported by the USDOE under Cooperative Agreements DE-FC52-06NA27616 & DE-NA0002075.

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NEVADA TERWATT FACILITY

Scientific Programs

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Negative Ion Photodetachment Studies Through Velocity-map Imaging Spectroscopy

K. Chartkunchand1, K. R. Carpenter1, V. T. Davis1, P. A. Neill1, J. S. Thompson1,

A. M. Covington1, T. J. Kvale2

(1)Department of Physics and Nevada Terawatt Facility, University of Nevada, Reno, MS 220 Reno, Nevada 89557-0058

(2)Department of Physics and Astronomy, University of Toledo, Toledo, Ohio 43606-3390

Award Number(s): DE-FC52-06NA27616, DE-NA0002075

Negative ion photodetachment studies provide insight on properties of the anion and its neutral parent, as well as dynamical information on the collision process itself [1]. The fact that a neutral “core” is left behind after photodetachment means that subtle interactions such as electron correlation and relativistic effects can be studied without being overshadowed by the long-range Coulomb interaction present in photoionization of neutral or positively-charged species.

The technique of Velocity-Map Imaging (VMI) spectroscopy [2] has recently been implemented at the Anion Research Center (ARC) at the University of Nevada, Reno. In the VMI technique, a series of electrostatic elements, as shown in Fig. 1, are used to project the full photoelectron distribution onto a position-sensitive detector monitored by a CCD camera. The key attribute of the VMI spectrometer is that the photoelectron distribution is projected in such a way as to ensure that photoelectrons with the same detachment velocity are mapped onto the same point of the detector regardless of their initial position in the interaction region. The VMI technique offers several advantages over more traditional electro- and magnetostatic spectroscopic techniques, including much greater detection efficiencies, and the ability to simultaneously collect photoelectron kinetic energy (PEK) spectra as well as photoelectron angular distributions (PADs). From the PEK spectra, structural information about the negative ion as well as properties such as the electron affinity (EA)

of the parent neutral can be determined. For linearly-polarized light, the relationship between photoelectron intensity and ejection angle takes on the form,

( ) ( )[ ]θβπ

σθ cos14 2PI += (1)

where σ is the total photodetachment cross-section and P2(cosθ) is the second-order Legendre polynomial. PAD measurements help determine the asymmetry parameter β. The asymmetry parameter, which is in general energy-dependent, completely characterizes the shape of the photoelectron emission pattern.

Fig. 1. Schematic of the VMI Spectrometer.

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Preliminary studies using the VMI technique have been performed on the isoelectric sequence Ge-, Sn-, and Pb-, as well as on the sulfur negative ion. In examining the Ge- and Sn- PEK spectra, we see a feature corresponding to a transition from the negative ion ground state to the first excited state of the neutral. Such a transition is nominally forbidden by LS-coupling selection rules. However, in this case the neutral excited state is better described by an admixture of configurations instead of a single LS configuration. This has been shown theoretically in the case of neutral tin [3] but the fact that this also holds for the lighter neutral germanium, albeit to a much lesser extent, has not been previously suspected.

Fig. 2. Ge- Photodetachment Image.

Fig. 3. Ge- PEK Spectrum.

The S- photodetachment studies have focused on the energy-dependence of the PADs near photodetachment thresholds. Due to the detachment of a p electron from S-, the interference between outgoing s and d partial-waves governs the overall PAD. The behavior of β in this case is given by the Hanstorp model [4],

( ) ( )22

2

22

2122

εεε

εβA

cAA+

−= (2)

where ε is the photoelectron kinetic energy and A2 and c are species-dependent parameters. The Hanstorp model is predicated on the threshold behavior of the photodetachment cross-section given by the Wigner threshold law [5]. It is thus crucial to know the range of validity of the threshold law. By determining the value of the asymmetry parameter as we approach a given photodetachment threshold and comparing it to that predicted by the Hanstorp model we will hopefully be able to answer that question.

Fig 4. S- Photodetachment Images at 573 nm to 614 nm Laser Wavelengths. [1] S. Manson and A. Starace, Rev. Mod. Phys. 54 (1982) 389. [2] A. T. J. B. Eppink and D. H. Parker,

Rev. Sci. Instrum. 68 (1997) 3477. [3] P. Oliver and A. Hibbert, J. Phys. B: At.

Mol. Opt. Phys. 41 (2008) 165003. [4] D. Hanstorp, C. Bengtsson, and D. J. Larson, Phys. Rev. A 40 (1989) 670. [5] E. P. Wigner, Phys. Rev. 73 (1948)

1002.

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Multi-parameter Characterization of Laser Ablation Plumes

J.J. Iratcabal, P.A. Neill, T.W. Darling, and A.M. Covington

Nevada Terawatt Facility, Department of Physics, University of Nevada, Reno, MS 220 Reno, Nevada 89557-0058, United States


A new experimental platform has been developed to characterize the properties of laser ablation plumes. The experimental system has been designed to survey a wide variety of target materials and geometries using high-repetition-rate lasers. Physical parameters of the plumes are being measured with a powerful array of spectroscopic instruments, optical laser probes, and charged particle analyzers. Experimental efforts are being guided by calculations. Characterization of ablation plumes containing neutral and ionized atomic and molecular species provides measurements useful in the HEDP, astrophysical, and technological fields.

Laser ablation plumes play an increasingly important role in HEDP research. Ablation plumes are complex environments which require the simultaneous measurement of many physical parameters to be fully characterized. Plumes produced by low intensity (I~107 to 1010 W/cm2) laser pulses generate plasmas composed of both molecules and atoms which are in ionized and neutral states. A particular difficulty for the spectroscopic modeling of these plumes is the large density of accessible states which are observed. Experimental measurements are required to guide the theoretical modeling of these plumes. This type of plasma plume is useful for studying stellar atmospheres, molecular opacity, thin film deposition, and novel HEDP targets [1-2]. Additionally, plumes created with low-intensity lasers provide a lower boundary condition for the plumes created by higher-intensity femtosecond-scale lasers. The use of pre-ionized plasma targets could help ameliorate certain issues inherent to gas and solid Z-pinch targets. Such pre-ionized targets could be created by low-intensity laser

ablation. The rate of plasma instability growth in plasmas is known to be highly sensitive to the boundary conditions of the targets used [3]. These issues increase the complexity in the boundary conditions of these highly non-linear systems and make it extremely difficult to accurately model plasma phenomena.

Lasers provide precise spatial and temporal manipulation of plume parameters. Laser fluence can be changed to tune the amount of mass ejected. Laser parameters can also be adjusted to alter the charge balance in the plume early in ablation. These plumes can also be backlit with an X-pinch to conduct opacity experiments. Opacity measurements involving molecules in plasmas are particularly important for studying the outer atmosphere of stellar objects.

A new, state-of-the-art, multi-parameter Laser Ablation Plume Experiment (LAPeX) apparatus has been designed, fabricated, and commissioned to capture data from a large number of physical parameters following the laser-induced ablation of a solid target. LAPeX plasma diagnostics employed include two time-gated UV-visible-NIR spectrometers, a VUV spectrometer, and an X-ray streak camera. Plume images can also be captured using a time-gated ICCD camera. Plasma shadowgraphy, as well as planned interferometry, is available to study plasma plume structure and velocity. A time-of-flight spectrometer is under development that will be used to measure the ionic charge state distribution and ion and electron kinetic energies within the plume.

All time-gated diagnostics will be synchronized on a master clock to provide an event-mode capability for the data acquisition system. At present, the ablation

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events will be produced by the use of one of several compact high-repetition-rate lasers. These include a Continuum Minilite 50 mJ Nd:YAG laser with ~5 ns pulse length and a Continuum Powerlite ~1 J ND:YAG laser with a ~5 ns pulse. The laser intensity on target ranges from ~106 to 1010 W/cm2, which allows for the production of atomic and molecular plasmas with increasing ionization fraction. Future experiments will also utilize NTF Leopard and Cheetah Laser Systems capable of creating relativistic plasmas with far higher initial charge states.

The entire laser ablation experimental chamber environment is carefully controlled using vacuum pumps and a gas handling system. The background pressures in the experimental chamber can be controlled and span ~1x10-8 to ~760-Torr. This allows plume formation to be studied across a wide range of pressures using different background gases. Another dimension of this experimental effort uses the NTF Materials and Target Fabrication Laboratory (MTFL). It has been shown that layered targets can be used to collisionally confine ablation plume dynamics [2], and the MTFL will allow us to create and test novel layered HED plasma targets with different geometries that ablate into multi-component plasma targets. Electric and magnetic fields can be applied to alter plume characteristics.

Currently, there are spectroscopic measurements being made for the ablation of graphite. In calendar year 2014, a number of specific experiments are planned to characterize laser ablation plumes. In the spring semester, and through the summer, laser ablation of graphite will continue. Laser ablation of aluminum and transition metal targets will begin at this time. Various target geometries will be tested. The data from preliminary experiments will help to elucidate the fundamental mechanisms controlling plume growth. Specific outcomes sought for each target include control and confinement of ablated mass, measurement of total charge liberation, as well as the measurement of plume characteristics such as charge state, density distributions, and velocity profiles.

Spectroscopic measurements will provide insight into the atomic and molecular dynamics of the plume and will permit the analysis of the radiation transport properties of the plasma plume. Exploring the parameter space involving the initial conditions of the target material, laser pulse, background gas, and applied electric and magnetic field environment will define what parameters control plume quality and expansion. Over the next several years, these experiments will explore the use of low-intensity laser ablation plumes to study stellar atmospheres, HEDP targets, molecular opacities, and thin film deposition.

In conclusion, this effort aims to provide tunable laser ablation plumes that will be used to explore the parameters and evolution of laser ablation plumes. The newly commissioned LAPeX platform is a robust apparatus that can thoroughly characterize ablation plumes and will lay the groundwork for scaled up experiments on the NTF’s Leopard and Cheetah Laser Systems. [1] P.M. Kowalski, A&A 519 (2010) L8. [2] M.E. Sherrill, et al, Phys. Rev. E 76 (2006) 056401. [3] D.B. Sinars, et al, Phys. Rev. Lett. 105 (2010) 185001.

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Isotope Activation in Zebra Z-pinch

Z. McCormick, T. Darling, B. Hammel, J. Iratcabal, E. McKee and A. M. Covington

Nevada Terawatt Facility, Department of Physics, University of Nevada, Reno, Reno Nevada 89557-0058, United States

Award Number: DE-NA0002075

The activation of isotopes using alternatives to conventional cyclotron technology is of great interest to both the scientific and medical communities. Isotopes commonly used for positron emission tomography (PET) scans have primarily been produced using cyclotron technology. While this technology is well developed, it cannot produce large quantities of short-lived isotopes owing to limitations in ion beam intensity and other factors. It has been proposed that fast pulsed-power systems such as Zebra Z-pinch may be able to produce greater yields of short-lived isotopes in the HEDP regime. These isotopes might someday allow for faster imaging of rapid biological processes, etc. A major goal of this research is to test the feasibility of short-lived isotope production on a pulsed power machine.

Activation of shot hardware has been detected routinely during post-shot radiation scans of the Zebra target chamber following experiments that introduced deuterium into the Z-pinch plasma. However, very little is known about the nuclear activation mechanisms and a number of questions remain unanswered. For instance, is the source of isotope production from (d,n) reactions in the plasma or from beam-target interactions between accelerated deuterons and the cathode (or anode)?

Recently, more detailed studies have begun to shed light on these questions and indicate that many of the activated isotopes are coming from materials found in the shot hardware. By substituting the types of materials used in the anode, cathode and target wires or by alternating between H and H(D) wire treatments, we are starting to unravel sources of isotope production.

During most experiments, Type 304 SST hardware loaded with four H(D)-treated Pd wires twisted in an X-pinch configuration was used. Ions in the plasma are accelerated to sufficient kinetic energies to initiate a variety of nuclear reactions. Some of these collisions produce unstable radioactive isotopes that were detected with a nuclear coincidence detection system.

The detection system was used to detect coincident pair-produced 0.511 MeV gamma rays following β+ decay in an activated isotope. By pointing two NaI scintillation detectors at the activated sample, and setting a counter to trigger only when both detectors register a signal within a coincidence window (~2 µsec), the background count rate is significantly diminished. This technique allows for accurate detection of lower activity levels than would be possible with non-coincident detection schemes.

Immediately following a shot, a timer was triggered and shot hardware was removed from the chamber and transferred to a detection system as quickly as possible. Following transfer to the coincidence detector, the material activity was measured for as a function of time for several hours. The resulting decay curve was analyzed to determine the half-life of isotopes present.

A list of potential isotopes was compiled along with respective (d,n) activation pathways and measured cross sections. Measured Pd reactions are unlikely to lead to the measured activity. The most likely activated isotopes are native to the 304 SST shot hardware. Hence, we compared the fitted half-lives to all available isotopes to create a plausible identification of the activated species.

Preliminary analysis of decay curves indicates that 61Ni(d,n)62Cu and 29Si(d,n)30P are the most likely candidates for detected

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activation. Figure 1 shows a sample data curve with a fit to respective decay constants (t1/2, Cu = 9.673 min, and t1/2, P = 2.498 min).

It should also be noted that a background shot was taken with H-treated Pd, which yielded no discernible activation above background, strengthening the assertion that activated isotopes are daughters in (d,n) reactions.

To determine initial activity, the fit coefficients are used along with a previously measured counting efficiency for the coincidence system. The efficiency of the overall coincidence system was calibrated with a 22Na source of known activity. Based on this, the activities were ~0.20 nCi for 62Cu and ~8.6 nCi for 30P. The low abundances of 61Ni and 29Si in the shot hardware raise expectations that greater yields could be achieved with isotopically-pure hardware materials.

It is interesting to note the relatively low abundance of these materials in the shot hardware, which indicates that much greater activity may be attainable with enriched materials. Overall, H(D)-treated Pd wires resulted in radioactive hardware post-shot, whereas H-treated Pd wires resulted in no activity over background.

At present, it is still unclear where (d,n) reactions actually occur. The most straightforward possibility is a beam-target interaction wherein deuterons are accelerated by the magnetic field of the Z-

pinch into the cathode disk. A more convoluted path wherein material may ablate from the cathode or anode disks and travel through the plasma, colliding with deuterons and finally depositing onto the cathode disk is also possible.

It will be of great interest to investigate these phenomena further in an attempt to determine the activation mechanism. Measuring post-shot activity of both the anode and the cathode plates to determine if radioactive material is preferentially present on one or the other is another logical experiment step.

Fig. 1. Sample decay curve w/ double exponential fit

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Laser-produced Neutrons and Isotopes

Z. A. McCormick, P. Wiewior, O. Chalyy, and A. M. Covington

Nevada Terawatt Facility, Department of Physics, University of Nevada, Reno, Reno Nevada 89557-0058, United States

Award Number: DE-NA0001834, DE-FC52-06NA27616, DE-NA0002075

The production of neutrons and daughter isotopes via beam target interactions is well known in the accelerator-based nuclear physics community. With the advent of high-intensity lasers (I>1018 W/cm2), beams of MeV kinetic energy particles can now be produced by the extremely large electric fields produced during the interaction of an intense laser pulse and a thin metallic target [1-3]. If a secondary “catcher” target is placed in the path of the particle beam produced by the primary laser-target interaction, the catcher acts as a converter for protons and deuterons via (p,n) or (d,n) reactions. Hence, temporally short bursts of neutrons can be made. Many of these reactions are accompanied by the activation of daughter isotopes with a wide range of half-lives and potential uses. The NTF Leopard Laser System (15 J, 350 fs, ~1019 W/cm2) is well suited to accelerate protons and other ions via laser-target interactions. These investigations aim to use laser-accelerated protons and ions to develop new types of target materials and geometries that will maximize neutron and isotopic yields and help to study the feasibility of laser-based production efforts.

The converters of immediate interest for n-production are lithium fluoride (LiF) via the 7Li(p,n)7Be channel, and elemental copper through the 63Cu(p,n)63Zn and 65Cu(p,n)65Zn channels. These processes have endothermic Q-values ranging from -4149 keV to -1644 keV [4]. The endothermic nature of these reactions requires that incoming protons have sufficient kinetic energy to overcome an activation energy threshold. The LiF (p,n) reaction cross section indicates protons ranging from 1 to 50 MeV are needed for the channel to open. The overall production

scheme is being modeled using the Monte-Carlo n-Particle (MCnP) code, which was recently installed on the NTF computational cluster. Preliminary measurements indicate that the peak of the proton energy spectrum will need to be matched to the peak of the (p,n) reaction cross section (~4 MeV) to optimize conversion efficiency. Preliminary measurements using protons and LiF as a converter have given yields ranging from 105-106 n per shot as determined by bubble counters.

Of further interest is the use of deuteron H(D) interactions for neutron production. Surface treatment of thin target foils with H(D) rich compounds have been seen to produce deuterons via laser-target interactions [2,3]. A bright laser produced D+ beam is attractive since the Q-value for 7Li(d,n)8Be is 15031 keV and is energetically favorable when compared to the 7Li(p,n)7Be reaction [5]. A gas treatment system has been developed in the NTF Target Fabrication Laboratory (TFL), which is capable of heat-treating metals such as Pd or Ti with D2 or H2 gas at high T and P. These metals provide near solid density H or H(D) rich targets. Prior investigations have concluded that the ejected proton beam is a result of hydrogen-bearing surface contaminants such as water vapor or hydrocarbons that are accelerated by the Target Sheath Normal mechanism [2]. A contaminant monolayer can coat a target in a few seconds at the pressure found in the experimental chamber (~1X10-5 Torr), so minimizing time between treatment and laser-target interaction is of utmost importance [1-3]. To this end, we are developing in situ treatment processes wherein H can be deposited at varying temperatures in the target shortly before the laser shot. Other deuterium-rich catcher

16

materials are also being explored including LiD2 to help increase the number of d-d reactions and overall n-yields.

Isotope activation processes utilizing appropriately chosen converters could quickly and relatively inexpensively create medically relevant isotopes- especially those used in Positron Emission Tomography (PET) scans. PET scan isotopes have been chosen since the laser-accelerated protons are a possible replacement for current cyclotron-based production techniques and also because coincidence techniques employed in these experiments simplify isotope detection and identification. For example, cyclotron efforts use N2 gas as a converter to create 11C, an isotope commonly used in PET scans, via the 14N(p,n)11C pathway. This isotope is also readily accessed through the 11B(p,n)11C channel. As a proof of concept investigation, the use of boron nitride (BN) as a converter will be implemented. For a more medically accessible technique, a gaseous N2 target or a nitrogen-enriched liquid cryogenically frozen to the target surface could be used. These possibilities will require significantly more engineering, and will therefore be considered after proof-of-principle has been achieved. Once successful, this technology could be adapted to activate a wide range of medically relevant isotopes. The ease of use and cost of this process could lead to the possibility for tailoring isotopes to medical need rather than availability.

At the time of writing, we are developing a Thompson parabola to measure proton energy spectra from a variety of laser targets. Once these have been characterized, open nuclear reaction channels can be determined. Thereafter, targets and laser parameters will be optimized to increase isotopic yields. Neutron Time-of-Flight detectors have also been developed which are capable of measuring neutron kinetic energy spectra. These detectors are robust, and can be used on Leopard and Zebra experiments. Currently, there are many factors that affect shot-to-shot variability, including: focusing parameters, foil target size, as well as foil and converter

positioning. If the variability of these parameters can be minimized, more reproducible results will be realized and the viability of these sources tested. [1] M. Storm, S. Jiang, D. Wertepny, C. Orban, J. Morrison, C. Willis, E. McCary, P. Balencourt, J. Snyder, E. Chowdhury, W. Bang, E. Gaul, G. Dyer, T. Ditmire, R. R. Freeman, and K. Akli, Phys. Plasmas 20, 053106 (2013). [2] A. Maksimchuk, A. Raymond, F. Yu, G. M. Petrov, F. Dollar, L. Willingale, C. Zulick, J. Davis, and K. Krushelnick, Appl. Phys. Lett. 102, 191117 (2013). [3] C. Zulick, F. Dollar, V. Chvykov, J. Davis, G. Kalinchenko, A. Maksimchuk, G. M. Petrov, A. Raymond, A. G. R. Thomas, L. Willingale, V. Yanovsky, and K. Krushelnick, Appl. Phys. Lett. 102, 124101 (2013). [4] N. Soppera, E. Dupont, M. Bossant, JANIS Book of proton-induced cross-sections, OECD NEA Data Bank, June 2012. [5] N. Soppera, E. Dupont, M. Bossant, JANIS Book of deuteron-induced cross-sections, OECD NEA Data Bank, June 2012.

17

Deuteriding Solids for Zebra and Leopard Targets

T. W. Darling and A. M. Covington

NTF, Department of Physics, University of Nevada, Reno, MS 220, Reno, Nevada 89557-0058, Award Number(s): DE-FC52-06NA27616, DE-NA0002075

Deuterium nuclei collisions are a low-threshold [1], non-radioactive source of quite monoenergetic neutrons with energies near 2.45 MeV. Z-pinches can produce regions of very high electric fields to accelerate deuterons above threshold, and neutrons are observed from deuterium-loaded targets. The target form can be a gas puff [2], an extruded strand of frozen deuterium [3], deuterided plastic filaments [4], and palladium metal permeated by interstitial deuterium [4,5]. This last target is appropriate for the NTF’s extensive experience with metal fine-wire loads, since the palladium retains its metallic character at high Pd / D ratios. This technique can also be used for modifying foil targets used in the Leopard laser experiments for MeV-energy deuteron production. The permeability of Pd to hydrogen and its isotopes has been used for decades as a heat-controllable leak valve for accelerator ionization stages. We process the assembled wire arrays in vessels (fig. 1) that can keep the wires pressurized in D2 gas until needed for loading.

Fig. 1. Wire Processing Pot for Deuteriding /Hydriding Pd Wires in Hardware.

While the wire format is convenient

for us, the geometry and dimensions make

some knowledge of the mobility of the deuterium in the Pd lattice essential. We have measured the resistance of a 20µ diameter Pd wire as it is loaded with deuterium from the gas phase at high temperature and then exposed to atmosphere and vacuum at low temperature where deuterium can escape from the wire.

Fig. 2. Resistance Measurements.

Fig. 2 shows the resistance as a function of time with temperature and gas pressure conditions. The resistance saturates at each gas pressure, and the increase in resistance achievable diminishes rapidly above about 100 psi and 100 C. By comparison with published data [6] we assert that the saturation D/Pd ratio is ~0.7. At room temperature there is a rapid drop in resistivity in both air and vacuum followed by a linear decrease, then an exponential decay. This is due to the departure of scattering centers as deuterium evaporates from the wire. Our main concern is that we lose too much deuterium to provide a reasonable density in the Z-pinch. Note that the linear drop in air is more rapid than in vacuum – we believe this is due to the formation of D2O by combustion at the surface followed by enhanced desorption, beating out the association and desorption processes for D2. The correlation between the concentration of deuterium in the lattice

18

and the resistivity is complicated by the existence of a phase transformation which is a function of concentration. Below a few percent, the α-phase has the lattice parameter near pure Pd and a scattering contribution from interstitial deuterons distributed at one atom per unit cell. Above about 50% concentration the β-phase, there is an expanded unit cell driven by unit cells containing two interstitials. Between these boundaries, the α and β phases coexist in varying fractions, introducing an additional disordered scattering component. The resistivity due to the addition of deuterium then has three regions, which along with concentration variations, must be accounted for. Since we do not measure explicitly the amount of deuterium absorbed or evolved, the total amount of deuterium in the target is modeled. As a function of time this is estimated by using radial diffusion and a simplified resistivity model of linear segments for the three regimes. A plot of a functional form for the resistivity from thin film data appears in [6]. This model divides the wire into annular sections and assumes that the initial distribution of deuterium is uniform at saturation. When the external environment changes to either vacuum or air, the atoms near the surface may escape with a given probability, thus decreasing the concentration in the outer annulus. The probability of diffusion between interior annuli is a function of the concentration (chemical potential) difference. The total resistance is determined by evaluating the resistance of each annulus using the resistivity-concentration model and summing the contributions as parallel resistors. The model is capable of reproducing the three regions observed as shown in fig. 3. The corresponding resistivity is shown in the inset.

Currently we are varying the parameters of the resistivity model to match the scale of these behaviors to the observations of fig. 1. The differences in the gradient of the linear section are modeled by enhancing the escape probability from the surface in the air-exposure case. The cylindrical geometry is important here and

gives different results to thin film measurements. The summed amount of deuterium in the wire is shown in red below the resistance curve. It is clear that the deuterium departs much more quickly than the resistance drops, making this modeling critical to the assessment of deuterium in the targets.

Fig. 3. Initial Model Output for Resistance and Deuterium Loads as a Function of Time. At room temperature deuterium departs quite rapidly from a thin wire, unlike the behavior of a Pd leak source in ionizers. This means that the time between processing and shooting both wire targets in Zebra and thin foil targets in Leopard is a critical factor and needs to be as short as possible. The ultimate fit from this model will provide information on the α−β phase transformation properties in the Pd-D system, as well as a quantitative assessment of the amount of initial deuterium in our targets. [1] R. E. Brown and N. Jarmie, Phys. Rev.

C, 41, pp1391-1400, (1990) [2] C. Coverdale et al., Phys. Plasmas, 14,

022706-1..7, (2007) [3] S. J. Stephanakis et al. Phys. Rev. Lett.

29, pp568-569, (1972) [4] A. Shyam and R. K. Rout, IEEE Trans. Plasma Sci., 27, pp1210-1213, (1999) [5] T. Darling et al. NTF review poster

(2010) [6] F. Scaramuzzi, J. Alloys Comp. 385,

pp19-27, (2004)

19

Developing Experimental Methods to Study the Dynamic Compression of Materials at the Nevada Terawatt Facility

B.D. Hammel, A.M. Covington, T.W. Darling

Department of Physics, University of Nevada, Reno, MS 220, Reno, Nevada 89557-0058, United States


Extraordinarily high pressures and temperatures can be created in materials as a result of shock waves propagating through them. In a laboratory setting, this can be accomplished via the impact of an ultra-fast projectile (flyer-plate) or via momentum transfer from surface ablation due to direct energy deposition. Although the flyer velocities and shock pressure regimes reached by large facilities (e.g. Sandia Z machine) are unmatchable, NTF’s pulsed-power machine can perform scaled experiments, exploring the same phenomena as Z, but at a higher repetition rate. The ability to perform such experiments will provide unique insights into shocked materials, as well as a staging area for detector development and for demonstrating experimental feasibility prior to preforming experiments at Z.

Initial flyer experiments on Zebra were exploratory and done as a proof-of-principle. Flyers consisted of 50 µm thick foils 1-3 mm away from the cathode return. Although it was inferred that velocities greater than 8 km/s were reached, the foil-flyers were not in a solid state [1]. Moreover, significant electrical breakdown was observed between the anode and cathode, possibly due to the material being vaporized.

Recent experiments have eliminated breakdown between the anode and cathode by redesigning the strip-line setup [Fig 1].

Fig. 1. Strip-line Flyer Design.

However, technical difficulties have been encountered. The larger size of the assembly allows some current to bypass the flyer. Moreover, the increased inductance was enough to reflect a portion of the current back through the system before it reached the load (flyer). An effort is currently underway to better understand these phenomena, and improve the coupling of the strip-line design to the system.

Concurrently, other options are also being explored. It is possible that Zebra's current parameters (100 – 200 ns current rise time) are more suited to unconventional methods of launching flyer-plates, such as the “electric-gun” design described by Weingart et al. [2]. The electric-gun utilizes a thin foil that, when ohmically heated, explodes and acts as a driving fuel for a separate, thicker, flyer-plate. Although this approach has had a lot of success at the Lawrence Livermore National Laboratory, we have encountered similar problems with electrical breakdown as we did with the foil-flyer.

Using pulsed plasma-jets as a drive for high-pressure experiments is a relatively new approach and has only received a small amount of attention in the shock-physics community. However after recent observations, this method has proven its feasibility of driving high pressures for a relatively long period of time (> 100 ns) [Fig. 2].

Ampleford [3] describes the formation of such plasma jets through conical wire arrays. The propagation of the jet in this geometry is largely determined through the hydrodynamic flow of ablated material from the wires. As a conical wire array implodes, a strong pressure gradient accelerates a jet of plasma out of the wire array at ultra-high velocities (~200 km/s) [3].

Flyer Anod

e

Cath

ode

20

Fig. 2. Top: Sectioned Sample at point of jet impact of copper anode. Bottom: Magnified image of jet impact location.

Fig. 3. Plasma-jet Experimental Configuration.

At the NTF, the impact from such plasma-jets was observed during an experiment using a standard x-pinch wire array [Fig. 3]. The impact drove a strong shock, energetic enough to scab off the free surface and create significant internal spall [Fig. 2]. However, for this to work as a reliable method of preforming high-pressure experiments, the drive parameters must be clearly understood. As of now, the mechanism that generates this shock is still under investigation. We suspect a large contribution is also due to an electron beam from the current. The impact of this beam onto the anode could create ablation and drive the copper similar to a direct-drive laser experiment. The primary thrust of upcoming campaigns is to obtain a more realistic time-profile of the drive.

Due to the rapidity of these processes, fast diagnostics are required to determine the consequences of the test. Although Neutron Resonant Spectroscopy and pulsed X-ray backlighting are used to probe the inside of materials subjected to dynamic compression, these diagnostics are difficult to field. Optical reflection data from an interface of the solid is preferred. In effort to characterize the conditions generated form the previously described methods; we have

developed a VISAR (Velocity Interferometer System for Any Reflector) in both a point-VISAR and line-VISAR configuration. These diagnostics have yet to be fielded, due to reliable access to sufficient digitizers (white-light streak camera, and fast photo-diodes) in addition to access to a high-powered CW single-mode laser source. Photon Doppler Velocimetry (PDV) is also being explored as an option.

The rapid energy deposition of the NTF’s pulsed-power generator has been used to force matter into extreme states through both direct deposition (direct-drive ablation) and the impact of fast projectiles (flyer-plates). Ongoing work is focusing on optimizing these processes and developing reliable diagnostics for characterizations of the conditions generated from such environments. [1] S. Neff, et al. High Energy Density Physics 6 (2010) 242-245 [2] D. Ampleford, Ph. D. Thesis, University of London, Imperial College, 2005 [3] R.C. Weingart et al. Livermore, Calif.: Dept. of Energy, Lawrence Livermore Laboratory.1979.

21

Production and Measurement of Fast Neutrons at Zebra

E. McKee, T. W. Darling, A. M. Covington, B. Hammel, J. Iratcabal, Z. McCormick, P. Neill

Department of Physics, University of Nevada, Reno, MS 220, Reno, Nevada 89557-0058,

United States


Neutron diagnostics are an essential part of all HEDP experiments as they are a clear indicator of nuclear interactions. Neutrons from dense X-pinched plasmas using wire arrays that have been treated to hold deuterium have yields that are routinely close to 109 neutrons. While this yield is moderate compared to Z or NIF, it provides a repeatable, pulsed source of neutrons for the development and calibration of neutron diagnostic apparatus.

The mechanism for describing the origin of these neutrons from Z-pinch plasmas has been discovered not to be thermonuclear in origin, but derives instead from accelerated ion collisions caused by intense fields located in the instability regions of the plasma [1]. The plasma is generated between the electrode gap of the HDZP-II 1-MA pulsed-power machine built at Los Alamos [2]. Accompanying the plasma creation are bursts of bright x-rays that saturate scintillators. Furthermore, EMI can negatively impact neutron detectors, impeding neutron yield and spectra measurements.

Discussed here are results from experimental outcomes involving neutron production and detection. Additional efforts have been directed at modeling detector responses from neutron interaction using the particle transport code Monte Carlo N-Particles (MCNP). Included in this are simulated designs for time-of-flight (TOF) detectors and threshold activation techniques using an input deck that contains detailed geometries.

The Zebra 1-MA/70 ns rise-time pulsed-power generator was initially designed to pinch single extruded wires of frozen deuterium in an effort to achieve fusion ignition [2]. However, solid thin-

wire loads are now the main target. In general, the load commonly used is a 4-wire, 20 μm palladium wire diffused with deuterium gas. The details of the wire-array target loads used in these experiments are discussed elsewhere [3].

Our approach has been to build on the wire-load experience at the NTF to make a load with spatially constrained deuterium. This was achieved by pressure treatment of palladium wires in a treatment vessel. The deuterium permeates the palladium metal when under high pressure and temperature (100-200 psi/80-125 C), and gets trapped in the interstitial matrix when the load is cooled. Resistive measurements have been made to determine deuterium concentration in the palladium, which yields a nearly 1:0.7 ratio at saturation.

The total neutron yield was measured with two independent types of detectors: 1) bubble-gel detectors and 2) isotope activation detectors. The bubble detectors were used only for order-of-magnitude estimates of yield. The isotope activation detectors do not directly measure neutrons but instead detect secondary particles produced from nuclear interactions with the neutrons. In the future, two different types of isotope activation detectors will be used to measure yield: 1) neutron capture diagnostics that are currently employed on Zebra and 2) threshold activation detectors that are currently under development.

LLNL has loaned the experimental team the use of neutron capture detectors. The principle of this activation detector is the detection of beta particles from the decay of Ag 110 and Ag 108 which can be distinguished from one another due to differing respective half-lives. This method relies on the moderation of the fast neutrons

22

to achieve a large capture cross value and is therefore sensitive to neutron scattering events.

Threshold activation relies not on non-capture event interactions with nuclei,

Fig. 1. MCNP Output of a Simulated PHA From NaI Detectors using Gaussian Energy Broadening for the 908 keV Characteristic Peak. but instead on inelastic neutron scattering leaving the target nuclei in an excited state. An yttrium slab was chosen because it is mono-isotopic, has a 0.9 MeV energy threshold for the reaction to take place, and a relatively short half-life at 15 seconds. The advantage of this detection method is the direct measurement of the 2.45 MeV neutrons, with a <1% contribution from environmental neutron scattering events created during the plasma event.

Fig. 2. TOF Signals due to the Saturating Effect of Hard X-rays. Four inches of lead was added between shots 130606 and 130607, where the scale is in volts and seconds.

Previous work on determining the spectra and timing of neutrons coming out of the pinch has been unsuccessful. High

fluxes of hard (>100keV) x-rays, presumably created by Bremsstrahlung from fast ions and electrons in the hot plasma has normally swamped the scintillation detectors. Fig. 2 shows the effect of the addition of several inches of lead shielding to the detection system. This shielding was not sufficient, as the expected neutron signal is still well below the x-rays saturating effect.

Overcoming this x-ray flux is important in many HED experiments. We are pursuing two strategies: 1) Shield–and-gate in which we separate (in time) the x-ray and neutron signals and optimize the x-ray shielding and 2) the “inverse gun” geometry, in which we use overwhelming shielding to prevent all direct radiation from reaching the detector, and provide low-Z scattering material to preferentially scatter neutrons into the detector. Using either of these methods requires knowledge of the background environment scattering, which we model, along with detector response using the Monte Carlo code MCNP.

The neutron production capabilities at NTF have routinely yielded neutrons per shot. Realization of neutron TOF measurements is important in experiments such as neutron resonance spectroscopy and laser-produced neutron experiments, in which the knowledge of the energy and timing of these neutrons is necessary. To this end, neutron work at the NTF has attracted the interest of national lab workers for studying the separation of neutron and x-ray signals.

[1] O. A. Anderson, W. Baker, S. A. Colgate, H. P. Furth, J. Ise, R. V. Pylse, and R. E. Wright. Neutron production in linear deuterium pinches. Phys. Rev., 110:1375-138, 1958. [2] J. S. Schlacter. Sold D2 fiber experiments on HDZP-II. Plasma Phys. Control Fusion 32:1073, 1990. [3] Darling et al, NTF review 2013

23

Current Redistribution and Generation of Kinetic Energy in the Stagnated Z-pinch

V. V. Ivanov1, A. A. Anderson1, D. Papp1, A. L. Astanovitskiy1,

B. R. Talbot1, J. P. Chittenden2, N. Niasse2

(1)Department of Physics, University of Nevada, Reno, MS 220, Reno, Nevada 89557-0058, United States

(2) Blackett Laboratory, Imperial College, London SW7 2BZ, UK

Award Number: DE-SC0008824

Since the 1950s, a wide variety of studies of Z-pinches have been initiated in connection with investigations on controlled fusion. However, some aspects of the sophisticated physics of the dense Z-pinch are still not well-understood. For example, mechanisms of enhanced plasma heating [1,2] have not been identified in experiments.

Faraday rotation diagnostics at a wavelength of 266 nm were developed at the Nevada Terawatt Facility, UNR. An optical schematic of the three-channel polarimeter for Faraday measurements is shown in Fig. 1. UV diagnostics allow investigation of the internal structure of the dense pinch [3,4]. UV Faraday rotation diagnostic allow measurement of MG magnetic fields in Z-pinches, as is shown in Fig.1.

We directly studied a structure of sub-MG magnetic fields and reconstructed the current distribution in the stagnated wire-array 1 MA Z-pinches using a Faraday rotation diagnostic at a wavelength of 266

nm [5]. It was found that a significant part of the current can switch from the main pinch to the trailing plasma, preheated by x-ray radiation of the main pinch if the inductance of the pinch rises due to sausage and kink instabilities.

Due to the complicated structure of the stagnated Z-pinch, Faraday images should be processed and interpreted carefully to derive quantitative data about

the magnetic field and current. Fig. 2 shows calculations of the rotation angle of the polarization plane of the probing beam in two plasma columns. Fig. 2 shows a positive angle of rotation in both sides of the dense pinch and a negative rotation angle in the left side of the first plasma column. Positive and negative rotation angles in simulations are seen as a lightening and a darkening, respectively, in the Faraday images. This analysis helps to interpret the configuration of magnetic fields in the Faraday images.

Areas of darkening and lightening are seen in experimental Faraday images as shown in Fig. 3. The configuration of the

Fig. 1. Optical Schematic of the Three-channel Polarimeter. The diagram compares rotation angles of the polarization plane of the laser beam at 532nm and 266nm in a plasma slab with an electron density of 1020 cm-3 and a length of 1 mm.

Fig. 2. The angle of rotation of the polarization plane of the probing laser beam at 266nm calculated for two closely located plasma columns with currents of 0.4MA and 0.6MA. Vertical lines show plasma columns.

24

rotation angles in many Faraday images qualitatively correlates with a model of current splitting in two plasma columns.

Configurations of plasma with splits or widely distributed currents were typical in wire-array Z-pinches. Secondary implosions of current-carrying trailing plasma provided additional kinetic energy. A thermalization of kinetic energy provided enhanced radiation of the Z-pinches.

The magnetic field in the dashed circle in the Faraday image was calculated using the Abel transform:

where β is the rotation angle and κ = 2e3λ2/(πm2c4). Rotation angles, α, in Faraday images were calculated using the shadowgram, Faraday image, and their reference images taken before the Z-pinch shot. The reconstructed magnetic field is presented in Fig. 3(f). The maximum strength of the magnetic field in the area of darkening is ~0.5 MG. The magnetic field calculated for current I = 0.32 MA fits the magnetic field reconstructed in the circle area in Fig. 3(b).

The UV Faraday rotation diagnostic unfolds the internal distribution of magnetic fields and allows the reconstruction of current in the Z pinch. Currents can switch from necks on the main pinch to trailing material due to the rising of inductance. Current redistribution impacts the plasma dynamics and radiative properties of the Z-pinch. Secondary implosions generate additional kinetic energy and enhanced radiation of Z-pinches. Secondary implosions can also explain enhanced radiation of Z-pinches in soft and keV ranges. The stagnation stage in Z-pinches is a complicated dynamic process with multiple internal implosions and collapses of micro-pinches.

[1] C. Deeney, T. Nash, R. R Prasad et al., Phys. Rev. A 44, 6762 (1991). [2] V.V. Ivanov,V. I. Sotnikov, J. M. Kindel et al., Phys. Rev. E 79, 056404 (2009). [3] V. V. Ivanov, J. P. Chittenden, S. D. Altemara, N. Niasse, P. Hakel, R. C. Mancini, D. Papp, and A. A. Anderson, Phys. Rev. Lett. 107 (2011) 165002. [4] V. V. Ivanov, J. P. Chittenden, R. C. Mancini et al., Phys. Rev. E 86 (2012) 046403. [5] V. V. Ivanov, A. A. Anderson, D. Papp et al., Phys. Rev. E 88 (2013) 013108.

Fig. 3. Shadowgram (a), Faraday image (b), and interferogram (c) of the pinch from implosion of an Ø16mm Al cylindrical wire array with eight 15 µm wires. The mismatch angle in the Faraday image is α0= +5.7º. (e) The rotation angle calculated along the dashed line in images (a)-(c) starting from the edge. (d) The plasma electron density Ne(r) reconstructed starting from the edge of the opaque pinch. (f) The reconstructed magnetic fields at the area of darkening in image (e) and the magnetic field calculated with a parabolic current density profile shown in diagram (g). (h) The timing diagram for the current pulse (1), total x-ray pulse (2), keV x-ray pulse (3), and UV frames (arrow).

∫−

−= 0

22

)(2)()( R

ye

rydy

yy

dyd

rrNrB β

πκ

25

Development of UV Laser Diagnostics for the Dense Z-pinch

V. V. Ivanov1, A. A. Anderson1, R. C. Mancini1, D. Papp1, A. L. Astanovitskiy1, B. R. Talbot1, J. P. Chittenden2, N. Niasse2, I. I. A. Begishev

(1)Department of Physics, University of Nevada, Reno, MS 220, Reno, Nevada 89557-0058, United States

(2) Blackett Laboratory, Imperial College, London SW7 2BZ, UK (3) Laboratory for Laser Energetics, University of Rochester, 250 East River Road, Rochester,

New York 14623, USA


We present the development of UV laser diagnostics at the Nevada Terawatt Facility, UNR. UV diagnostics at 266nm display a significant advantage over diagnostics at 532 nm. Absorption, refraction, and Faraday rotation angles in Z-pinch plasmas at 532 nm, 266 nm, and 211 nm are presented in Fig. 1. Critical plasma density, increment of the inverse

bremsstrahlung absorption, refraction angle, and Faraday rotation angle are all proportional to λ2. We have developed UV diagnostics including interferometry, side-on and end-on shadowgraphy, and Faraday

rotation [1-4]. Shadowgraphy with a spatial resolution of 5-8 µm shows the dense pinch in unprecedented detail. Two-frame diagnostics show fast plasma motion in the stagnated Z-pinches. Interferometry at a wavelength of 266 nm allows measurement of plasma densities in the range of (1-3)x1020 cm-3 in the ablating wires, imploding plasma, stagnating pinch, and trailing

material. Magnetic field structure and current distribution between the trailing plasma and stagnated Z-pinches were reconstructed using a Faraday rotation diagnostic. UV diagnostics allow direct

Fig. 1. (a) Transmission of the Al plasma with an electron temperature of 350 eV and a length of 1mm. (c) The refraction angles calculated for the plasma distributions (b). The Faraday rotation angle in the plasma with an electron density of 1020cm-3 and a length of 0.2mm.

Fig. 2. Interferogram (a) and shadowgram (d) at 266 nm show Z-pinches produced by implosions of the 20 mm-diameter, Al, 3-ray, 18-wire star loads,. Image (a) was taken 10 ns after the maximum of the x-ray pulse and image (d) was taken 24 ns after the maximum. A magnified image (b) is taken from the solid rectangle in interferogram (a). A magnified image (c) is taken from the complimentary shadowgram and the dashed rectangle in (a) shows the position of this image. Image (e) is taken from the dashed rectangle in (d).

26

investigation of the fine structure of the dense Z-pinch, the development of instabilities [2,3], and the distribution of magnetic fields and currents [4]. Micro-pinches and instabilities with characteristic scales of 15 - 200 µm were observed in 1-MA wire-array Z-pinches, as seen in Fig. 2.

Fig. 3 shows the fast plasma motion observed at the stagnation stage with two-frame shadowgraphy. The UV two-frame shadowgram shows the dynamics of necks and bulges in the pinch. Dashed circles represent two areas of formation of the plasma arm on the pinch. Arrows show the

areas of fast plasma expansion. Plasma motion at stagnation and prolonged implosion of the trailing mass both provide additional kinetic energy in the stagnated pinch, and can be a source of enhanced x-ray production.

A UV Faraday rotation diagnostic reveals a distribution of magnetic fields in the Z-pinch and trailing material. The magnetic field and current strengths were reconstructed from rotation angles and phase shifts in the plasma, using an Abel transform [4]. Current in the pinch can switch from the high-inductance neck and redistribute to the trailing material when resistance of the peripheral plasma drops due to heating by x-ray radiation [4]. Fig. 4 shows images from the 3-channel Faraday diagnostic. In this case, the load mass was too small for the Zebra generator and the implosion did not produce a compact dense pinch. An

interferogram displays the plasma over a wide area, while a Faraday image shows the current flows in a smaller central area. Current is identified by lightening in the right side and darkening in the left side of the image due to the magnetic field pointing in opposite directions in these areas.

Development of UV diagnostics at a 211nm wavelength will further improve optical methods as applied to Z-pinch plasmas in multi-MA pulsed-power facilities. A Nd:glass laser for operation at 263 and 211nm is being developed at the NTF for this purpose.

[1] S. D. Altemara, D. Papp, V. V. Ivanov, A. A. Anderson et. Al., IEEE Trans. Plasma Sci. 40 (2012) 3378. [2] V. V. Ivanov, J. P. Chittenden, S. D. Altemara, N. Niasse, P. Hakel, R. C. Mancini, D. Papp, and A. A. Anderson, Phys. Rev. Lett. 107 (2011) 165002. [3] V. V. Ivanov, J. P. Chittenden, R. C. Mancini, D. Papp, N. Niasse, S. D. Altemara, and A. A. Anderson, Phys. Rev. E 86 (2012) 046403. [4] V. V. Ivanov, A. A. Anderson, D. Papp, A. L. Astanovitskiy, B. R. Talbot, J. P. Chittenden, N. Niasse, Phys. Rev. E 88 (2013) 013108.

Fig. 3. Two-frame shadowgraphy at 266 nm, with 5 ns between frames, of wire-array Z-pinches from two shots. (a,b) The stagnation phase in a 10-wire Ni linear array.

Fig. 4. Shadowgram (a), interferogram (b), and Faraday image (c) at 266 nm taken from a 12-mm diameter, Al cylindrical 6-wire array,. The mismatch angle in the Faraday image is α0= +5.7º. (e) The timing diagram for UV diagnostics (arrow), current pulse (1), and x-ray pulse (2).

27

Study of the Internal Structure and Instabilities in the Dense Z-pinch

V. V. Ivanov1, J. P. Chittenden2, S. D. Altemara1, N. Niasse2, P. Hakel1, R. C. Mancini1,

A. D. Papp1, A. Anderson1, A. L. Astanovitskiy1, B. R. Talbot1,

(1)Department of Physics, University of Nevada, Reno, MS 220, Reno NV 89557-0058, United States

(2) Blackett Laboratory, Imperial College, London SW7 2BZ, UK Award Number(s): DE-FC52-06NA27616, DE-NA0002075

Dense and hot Z-pinch plasmas are used in a variety of high-energy-density physics applications. The peak power of the Z-pinch is limited by the fast growth of MHD instabilities at the stagnation stage. Regular laser radiation at 532 nm does not penetrate into the trailing material around the pinch due to strong absorption and refraction. The structure of the stagnated Z-pinch has been studied with x-ray self-

radiation diagnostics, from which one can derive a temperature map of the pinch with a spatial resolution of 60-100 µm.

High-resolution laser diagnostics at a wavelength of 266 nm were used to investigate Z-pinches at the NTF’s 1-MA pulsed-power generator [1-3]. The internal structure of the stagnated Z-pinches was observed in unprecedented detail. A dense pinch with strong instabilities was found inside the column of the trailing plasma. Kink instabilities, disruptions, and micro-pinches were seen at the peak of the x-ray

pulse and also at later times. The three-dimensional structure of the stagnated Z pinch depends on the initial wire-array configuration and implosion scenario.

Figure 1. Shadowgrams (a, b) and an interferogram (c) of the central part of the pinch at wavelengths of 532 nm (a) and 266 nm (b, c). The Z-pinch is produced by the implosion of a cylindrical 16-wire array 8 mm in diameter. Probing directions are presented in (d). The cathode is on the top of the images. Shadowgrams (a) and (b) were taken at 0.6 ns after the maximum of the x-ray pulse.

Figure 2. Shadowgrams at wavelengths 532 nm (a) and 266 nm (b) of the Z-pinch produced by an implosion of a cylindrical, 16 mm-diameter 16-wire array. (c) Magnified image of the area marked by the solid rectangle in shadowgram (b). X-ray frames from a pinhole camera filtered for E>0.8 keV (d) and E>3 keV. The diagram (f) presents the timing of the frames at 532 nm (diamond), 266 nm (solid arrow), and x-ray frames (stripes) to the current pulse (1) and keV x-ray pulse (2).

28

Small-scale density perturbations were found in the stagnated Z pinch.

Fig. 1 presents a central part of the cylindrical wire-array Z-pinch at 0.8 ns after the maximum of the x-ray pulse. The shadowgram (b) at 266 nm represents the area of the dashed rectangle.

The UV shadowgram shows strong kink instabilities with necks 90-150 μm in diameter hidden inside the rectangular area in shadowgram (a). Interferogram (c) at 266 nm represents an area of the solid rectangle

in image (a). The interferogram indicates plasma which may support current in the gaps. Fig. 2 presents micro-pinching in the dense pinch. Image (e) with a photon energy >3 keV shows a bright spot in the center of the pinch. The position of the bright spot correlates with the micro-pinch in Fig. 2 (a,b).

A high-resolution UV diagnostic allows for investigation of small-scale plasma instabilities in the stagnated Z-pinch. A slit was installed fore of the CCD camera to illuminate a central area of the pinch and block side-illumination by the intensive laser pulse. Perturbations on a scale of 10-30 µm were found in the stagnated Z-pinch plasma.

Fig. 3 (a, b) presents two-frame shadowgrams at a wavelength of 266 nm. The bulge plasma demonstrated a fast

motion at stagnation. Dashed rectangles in the UV frames show plasma moving with a speed of >100 km/s.

The observed development of instabilities is in agreement with 3D MHD simulations. The stagnation stage in the cylindrical and star wire-arrays were modeled with the 3D resistive MHD code Gorgon. The development of instabilities in

an Ø8-mm cylindrical array and a 4-ray star wire array were compared with experimental shadowgrams. Fig. 4 displays simulations of the electron density distribution, integrated along the line of sight in a Ø8-mm Al star wire array.

New UV diagnostics allow detailed investigation of the structure, instabilities, and plasma dynamics in the dense Z-pinch.

[1] S. D. Altemara, D. Papp, V. V. Ivanov, A. A. Anderson, et. al, IEEE Trans. Plasma Sci. 40 (2012) 3378. [2] V. V. Ivanov, J. P. Chittenden, S. D. Altemara, N. Niasse, P. Hakel, R. C. Mancini, D. Papp, and A. A. Anderson, Phys. Rev. Lett. 107 (2011) 165002. [3] V. V. Ivanov, J. P. Chittenden, R. C. Mancini, D. Papp, N. Niasse, S. D. Altemara, and A. A. Anderson, Phys. Rev. E 86 (2012) 046403.

Figure 4. (a-c) 3D MHD Gorgon simulation of the mass density integrated along the line of sight, in the cylindrical 16-wire array Ø8 mm. (d-e) Magnified 3D surfaces of the high density region (d) and electron temperature of this region (e) from two orthogonal views. (f) The timing diagram.

Fig. 3. Shadowgrams at 266 nm (a, b) and 532 nm (c), x-ray pinhole frames at E> 3 keV (c), and a timing diagram (d) from implosion of the Al linear 12-wire 10 mm array. The delay between frames (a) and (b) is 2.7 ns.

29

X-Ray Absorption Spectroscopy and Imaging for Wire-array Z-pinches

A.A. Anderson1, V.V. Ivanov1, D.Papp1, S.D.Altemara1,B. Talbot1, P. Hakel1, R.C.

Mancini1, J.P. Chittenden2, A.P. Shevelko3, P. Wiewior1,T.Durmaz1, A.L. Astanovitskiy1

(1)Department of Physics, University of Nevada, Reno, MS 220 Reno, Nevada 89557-0058, United States

(2)Blackett Laboratory, Imperial College, London SW7 2BZ, UK (3)Department of Physics and Astronomy, Brigham Young University, Provo, UT, USA

Award Number(s): DE-NA0002075, DE-FC52-06NA27616

Coupled experiments using the 50-

TW Leopard laser and 1-MA Zebra pulsed- power generator have been performed at the NTF. The combination allows for powerful Z-pinch laser-based diagnostics. Two such diagnostics have been developed, ablation spectroscopy and x-ray imaging, both of which use x-rays produced by the Leopard laser as a backlighting source during a z-pinch.

Plasma dynamics during the ablation and implosion stages of the Z-pinch seed into the stagnation stage and affect the quality of the pinch [1], and so measuring the electron density and temperature during these stages is important for understanding an imploding wire array Z- pinch. However, during these early stages of the Z-pinch, the plasma is too cold to use k-shell emission spectroscopy. Absorption spectroscopy has therefore been utilized to probe the plasma during these non-emission stages of the Z-pinch[2][3]. Laser-based absorption spectroscopy has the advantage of flexible timing and a wide choice of target materials over other absorption spectroscopy techniques.

Simulations showed strong absorption for Al plasma in the 1.45 keV to 1.55 keV range at low plasma temperatures of 10 to 40 eV. Different elements were tested as a backlighting source, and samarium was chosen because of its quasi-continuum emission in the range between 1.45 keV and 1.55 keV.

Two spectrometers were used in every shot. One spectrometer recorded the backlighting spectrum directly, while the other spectrometer measured the spectrum after it had been absorbed by the plasma. Reference shots with the x-ray backlighting were performed before every shot to account for variation in the backlighting spectrum.

Fig. 1. (a)Calibration shots for conical spectrometers using Sm and Mg as backlighting sources (b) Shot #2282, backlighting spectrum from reference spectrometer from laser only and laser z-pinch coupled shot(c) Shot to shot variation in two laser only shots in main spectrometer.

There are some difficulties with adapting absorption spectroscopy to study Z-pinches. The Leopard laser produces up to a 30J pulse, which produces an x-ray backlighting source with less than .1 J of energy in the keV range. The Z-pinch, on the other hand, has radiation in the keV range on the order 1 kJ. Collimators have been therefore employed to geometrically block the radiation from the Z-pinch from interfering with the backlighting source.

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Fig. 2. (a) Laser-only spectrum (red) and laser couple with z-pinch spectrum (black). (b)Transmission spectrum (red) compared to 2 temperature model (Te = 14eV and 30eV) and single temperature model (Te=20eV)

Transmission spectra were analyzed using the PrismSPECT atomic code and a two-temperature model was created. Results were compared to a 2-D MHD Gorgon simulation [2] with general agreement.

Monochromatic x-ray imaging of a wire array Z-pinch using spherically bent crystals is being developed to image Z-pinches during the ablation and implosion stages. Similar diagnostics have been developed in the past, and they feature high resolution and plasma penetration [4].

The backlighting source is the 6.65 Å Si Heα spectral line, produced by hitting a Si target with the Leopard laser. A spherically bent quartz 1011 crystal images the backlit pinch onto a film strip. The image is protected from undesired x-rays created by the Si target by the high spectral selection of the bent quarzt crystal, which has a spectral selection on the order of 10-4 [5].

Initial experiments have been able to successfully image 7.6 μm wires. Fig. 3

shows Ni wires in a laser-only shot (a) and during a laser and Z-pinch coupled shot (b).

Fig. 3. (a) Pre-shot x-ray imaging of 2 7.6 μm Ni wires using a spherically bent crystal. (b) Image of a 7.6 μm Ni wire during ablation stage of a wire array z-pinch.

The bent crystal is placed inside the

vacuum chamber, 2 cm inside the Rowland circle for the spherical crystal, where a collimator and a metal housing protect it from debris and from the x-ray burst from the main pinch. In addition, the film is blocked by copper-plated lead shielding to protect it from errant x-rays generated by the pinch.

Future experiments are planned, with better shielding to protect the image from secondary sources of radiation and to remove the noise seen in fig. 7b. [1] T.W.L. Sanford et al, Phys. Rev. Lett.,

vol 77 (1996) [2] V.V. Ivanov et al, Phys. Rev. Lett. 106.

225005 (2011) [3] V. V. Ivanov et al., HEDP 7, 383-390

(2011) [4] S.A. Pikuz et al. JETP Lett., vol. 61,

(1995) [5] D.B. Sinars et al, Appl. Optics, vol. 42,

(2003)

31

Investigation of Implosion Dynamics in Nested Cylindrical and Star Wire Arrays

D. Papp1, V. V. Ivanov1, B. Jones2, A. A. Anderson1, S. D. Altemara1, A. Haboub1, B. R.

Talbot

(1)Nevada Terawatt Facility, Department of Physics, University of Nevada, Reno, Reno NV 89557-0058, United States

(3)Sandia National Laboratories, Albuquerque, NM 87185, United States Award Number: DE-FC52-06NA27616, DE-NA0002075

Nested cylindrical wire array z-pinches are the most powerful laboratory x-ray sources, generating soft x-ray pulses of up to 1.9MJ in energy and 280TW of power1-3, and are used as K-shell x-ray sources in the 1-9keV range4-5. The mass introduced on an inner cylindrical array can suppress the development of magnetic Rayleigh-Taylor (MRT) instabilities during implosion, leading to higher power and a shorter duration of the x-ray pulse as compared to regular cylindrical loads1-3. Star wire arrays6 are multiple nested arrays with low wire numbers that generate reproducible x-ray pulses on a 1MA-scale machine.

Implosion dynamics and x-ray yields of nested cylindrical and star Al wire arrays were investigated on the NTF 1MA 100ns rise-time Zebra accelerator6-8. Gated star arrays have wire pairs replacing single inner wires. The transparent and nontransparent implosion modes of nested cylindrical arrays were reproduced in gated star arrays by changing the length and inductance of the gate wires7. Changing the configuration of the wire array can be used to tailor the inside magnetic field. This effect can be used to delay or advance the x-ray pulse compared to the current pulse time, while keeping array mass and x-ray yield unchanged.

In wire arrays, implosion starts by the j×B forces moving plasma from the ablating wires. Most wire arrays implode with precursor plasma forming on the array axis. The formation of the precursor can be suppressed by using large-diameter wire arrays5 or by changing the direction of ablative forces in star wire arrays8.

In closely-spaced nested cylindrical wire arrays, the inner and outer wires are

close enough so that the ablative forces on the inner wires point outward. It was found that the inward ablation is not completely suppressed, and has a strong dependence on the array wire number. For arrays with the same mass, the larger-diameter wires in lower wire-number arrays have higher mass ablation rates. As j×B forces are not increased, the speed of the ablating plasma streams is reduced. In wire arrays with 12-16 wires, the precursor formed during the ablation phase. In 8-wire arrays, as shown in Fig. 1(a), no plasma accumulated on the axis during the ablation phase. The axial plasma formation was delayed until the implosion phase [Fig 1(b)].

Figure 1. 532nm shadowgrams of 8-wire closely spaced array, Shot #2396. Frames are separated by 25ns. From [8].

In star arrays, the presence of the precursor was determined by the direction of the j×B forces on the inner wires. To

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separate the effect of the precursor on the pinch stability, star wire-array configuration pairs were designed, so that they would have or would lack precursor, while keeping implosion dynamics similar. Arrays without precursors produced 3-15% higher x-ray yields.

It was also found that decreasing the wire number (and symmetry) of star and nested cylindrical wire arrays improved the K-shell x-ray yield by up to a factor of two [Fig. 2]. Consistent with this finding, the 8-wire arrays imploded 15ns earlier than the 16-wire arrays, suggesting higher implosion speeds. From the analysis of the K-shell emission spectrum, the lower-wire number arrays were also hotter. 8-wire arrays had electron temperatures of 310eV, while 16-wire arrays had a temperature of only 270eV.

Figure 2. X-ray yields for star arrays in precursor and non-precursor configurations8

Another spectroscopic investigation focused on the cooling effect of high-Z materials in z-pinch and laser-produced plasmas. In z-pinch plasmas, the presence of 7% Au in Al planar wire arrays decreased electron temperatures from 300 to 260eV. In plasmas produced by the NTF Leopard laser in the ns-pulse regime, no cooling was observed. The temperatures of both Al and Al-Au laser plasmas were in the 460-480eV range. The spectroscopic model was built with the PrismSPECT code.

This work was conducted as my Ph.D. thesis research under the supervision of Dr. Vladimir V. Ivanov. [1] R. B. Spielman et al., Phys. Plasmas 5, 2105 (1998) [2] C. Deeney et al., Phys. Rev. Lett. 81, 4883 (1998) [3] T. W. L. Sanford et al., Phys. Plasmas 14, 052703 (2007) [4] C. A. Coverdale et al., HEDP 6, 143 (2010) [5]B. Jones et al., Phys. Plasmas 15, 122703 (2008) [6]V. V. Ivanov et al., PRL 100, 025004 (2008) [7]V. V. Ivanov et al., Phys. Plasmas 17, 102702 (2010) [8]D. Papp et al., Phys. Plasmas 19, 092704 (2012)

33

Developing Zeeman Broadening Diagnostics for Magnetized Plasmas at NTF

S. Haque, R. Presura, M. Wallace, A. Arias, N. Quiros, B. Largent

Nevada Terawatt Facility, Department of Physics, University of Nevada, Reno, Reno NV 89557-0058, United States

Award Number: DE-SC0008829, DE-FC52-06NA27616, DE-NA0002075 Magnetic field measurements are crucial in the study of many laboratory and astrophysical plasmas. In laser-produced plasmas where the energy is deposited over very short time scales, electric and magnetic fields with highly varying magnitude and orientation are present. Faraday rotation is a technique currently being employed at the Nevada Terawatt Facility[1] to determine the magnetic field distribution by using a polarized laser probing beam. This method relies on the anisotropy created in a plasma by the magnetic field and provides the integral along the beam path of the product between the electron density and the parallel component of magnetic. Magnetic fields in plasmas can also be measured using the Zeeman effect,[2] consisting in a splitting of the spectral lines in the presence of the field. However, in high energy density plasmas the Zeeman splitting components are broadened by the particle motion (Doppler) and density (Stark) effects and generally they can no longer be resolved. The goal of the present work is to implement a magnetic field diagnostic based on the Zeeman effect, proposed by Tessarin et al.[3] and by Stambulchik et al.[4] It can give information on the magnitude and orientation of the magnetic field even for cases when the field direction fluctuates over spatial scales (much) shorter than the plasma size. The basis for this technique is that different embers of an atomic multiplet undergo Zeeman splitting into different numbers of sub-components, and thus are broadened to different widths. With proper choice of atomic multiplet, the Stark and Doppler contributions to the line profiles are nearly identical. Thus, the difference in the line widths of the multiplet components depends only on the magnetic field.

The multiplet components must be chosen so that they may be resolved by the instrument for the expected plasma density and temperature. Because the difference in the multiplet component widths is given by the different number of sub-components, the individual Zeeman components need not be resolved. This method is particularly useful for plasmas in which Stark and Doppler broadening are much larger than the Zeeman splitting, as is the case in HED plasmas.

Figure 1: Schematic of experimental set up inside Zebra. Shown is the aluminum electrode and the location of laser impact. The arrows show the sight-lines of the high-resolution spectrometer. The first tests of the technique were performed using the Al III 2S1/2 - 2P3/2 and 2S1/2 - 2P1/2 doublet transition at 569.6 nm and 572.2 nm, respectively. This particular doublet has been analyzed extensively and verified for use up to ne=1018 cm-3 and B = 40 T.[3] A schematic of the experimental set-up is shown in Fig. 1. The Zebra pulsed power generator was used to create magnetic fields with peak strengths of ~40 T and 200 ns rise time. The Leopard laser (0.5 ns, 20 J) was focused onto the aluminum

34

electrode to produce plasma at various times during the Zebra pulse. Adjusting the moment of ablation with respect to the current maximum allows access to a range of plasma parameters and field strengths. High-resolution spectra of the plasma emission were obtained with a 1 m Acton Research instrument and recorded with a gated optical imager with exposure time 10 ns or longer. Spectra resolved in space along the radial direction were taken along a line-of-sight perpendicular to B using imaging optics. Space-integrated spectra were taken along a line-of-sight parallel to B using fiber optics. In principle, the magnetic field orientation can be inferred from the two spectra because encoded in the line width difference are two orthogonal projections of the orientation of the magnetic field. The transitions between the Zeeman-split levels are either σ- or π- polarized. The π components are only visible parallel to B, and both σ and π components are visible perpendicular to B.[5] The two spectra are expected to have different doublet component widths as a function of the actual field orientation.

Figure 2: Spectrum from Zebra shot #3136. Most spectra obtained exhibit the doublet components resolved and broadened to different widths. For example, Figure 2 shows a spectrum taken at approximately 0.5 mm from the electrode surface with a 10-ns time gate. The difference in Zeeman broadening corresponds to a field strength of about 16 T. For some shots, the Zeeman components were resolvable, yielding magnetic field measurements directly.

The results of recent experiments demonstrate that magnetic field dependent broadening of the 4s-4p Al III doublet

transition can be obtained with high-resolution. For a full implementation of this diagnostic, theoretical support is necessary for detailed line-shape modeling of the spectra, which would provide the plasma density and temperature in addition to the magnetic field strength.

Once this diagnostic has been tested thoroughly, its eventual integration into the diagnostic suite at the NTF will aid in answering many open questions of ongoing experiments at the facility. The application of this technique extends to a broad scope of pulsed-power and laser plasma experiments through the choice of atomic multiplet. It is well documented which transitions will be suitable for magnetic fields up to 3500 T in magnitude and densities up to 1022 cm-3.[3] In conclusion, this Zeeman broadening diagnostic method provides a passive measurement of the magnetic field structure in laboratory laser plasmas not available from existing methods.

We would like to thank our LLNL collaborators (especially H.-S. Park) for making the high resolution spectrometer available for these measurements. [1] V. V. Ivanov et al., IEEE Transactions on Plasma Science 34, 2247 (2006); doi: 10.1109/TPS.2006.877693 [2] E. A. McLean, J. A. Stamper, C. K. Manka, H. R. Griem, D. W. Droemer, and B. H. Ripin, Phys. Fluids 27, 1327 (1984); doi: 10.1063/1.864747 [3] S. Tessarin, D. Mikitchuk, R. Doron, E. Stambulchik, E. Kroupp, Y. Maron, D. A. Hammer, V. L. Jacobs, J. F. Seely, B. V. Oliver, and A. Fisher, Phys. Plasmas 18, 093301 (2011); doi: 10.1063/1.3625555 [4] E. Stambulchik, K. Tsigutkin, Y. Maron, Phys. Rev. Lett. 98, 225001 (2007). [5] Sobelman, I.I. (1979), “Atomic Spectra and Radiative Transitions”, 2nd ed. New York, NY: Springer-Verlag

35

2D Spatially-resolved Imaging Spectroscopy of Z-pinch Plasmas with Convex Bent Crystals

D. Papp, R. Presura, Z. Johnson, M. S. Wallace, S. Haque


Award Number: DE-NA0001834, DE-FC52-06NA27616, DE-NA0002075

Space- and energy-resolved x-ray imaging is one of the ultimate spectroscopic tools for high-energy-density plasmas, as it can provide the spatial distribution of different plasma parameters, such as electron density and temperature. Examples of such diagnostics methods include monochromatic x-ray backlighting1-3, where the backlit plasma is imaged by a spherically bent crystal. This technique is constrained to a limited number of matching line-crystal combinations. Another such instrument, the Multi-Monochromatic Imager4,5, combines the imaging of a pinhole array with the spectral dispersion of a multilayer mirror, and is widely used in diagnosing laser-produced plasmas.

We propose the development of a new 2D spatially resolved, time-integrated spectroscopic technique using low-cost cylindrically bent concave and convex crystal spectrometers for the investigation of laser and Z-pinch plasmas. The method proposed is based on the use of the strong source broadening of convex crystal spectrometers (Fig.1), which are used to record x-ray spectra over wide spectral ranges6,7.

Figure 1. Schematics of a Convex Crystal Spectrometer By using a slit in combination with a spectrometer, a one-dimensional image of

the source can be provided that is resolved perpendicular to the dispersing direction of the crystal. In case of such spectra recorded by convex crystal spectrometers, it is often noted that the shape of the lines themselves, as recorded on a medium, resemble the shape of the plasma source. This provides some crude resolution perpendicular to the spectral line along the dispersive direction, allowing development of 2D spatially-resolved spectroscopy of the x-ray source. Fig. 2 shows time-gated pinhole images and the spectra of an Al 5056 (containing 5% Mg) conical wire array Z-pinch plasma on the ZEBRA generator at the NTF. Note that the shape of the lines [Fig. 2(c),] resembles the shape of the emitting plasma recorded by time-gated pinhole imaging [Fig. 2(a), (d)]. The spectrometer had a KAP crystal with a 50.8mm bending radius, 900mm from the source. The physical size of the source (~ 1 mm) can reduce the resolving power (E/ΔE) of such spectrometers down to around 200.

In the Al 5056 wire array plasma, containing 5% Mg, the Mg lines have low opacity compared to the Al lines, and can be used for spectroscopic diagnostics purposes. In the experimental spectrometer, a convex KAP crystal is used to record the time integrated K-shell spectra of both Al and Mg, in the 1.2-2.5keV (5-10Å) energy range on KODAK Biomax radiographic film.

For the Al wire arrays, the K-shell radiation can be recorded by KAP crystal spectrometers, which contain a crystal with broad spectral range, high reflectivity and a narrow rocking curve9. Spectral features must be selected that can be used to determine ne and Te distribution in the plasma. Suitable lines should have low opacity, but still adequate intensity. The

36

separation from neighboring high-intensity lines should be large enough so that the lines will not overlap from source broadening. Generally, low principal quantum number resonance K-shell lines fit these criteria, except very strong lines like Al He-α and Ly-α, which have high opacity. Satellite line features usually merge at low resolving powers, are of lower intensities, and usually are not adequately separated from the resonance lines. Spectroscopic modeling will be developed with the PrismSPECT code10.

Figure 2. Time-integrated (1D-resolved with slit) spectra recorded by convex KAP crystal spectrometer, for two conical wire arrays. Configuration of the wire array and time-gated pinhole x-ray images (a) for a “regular” conical wire array, and K-shell spectrum (b), and two selected lines stretched to display the spatial information in the direction of the spectral dispersion (c). From [8].

Implementing these diagnostics

requires improving the limited spatial resolution of the proof-of-concept method. Instrumentally, placing the convex crystal closer to the pinch would improve both the x-ray intensity incident on the film and the spatial resolution. The improvement achievable this way is limited by the line spacing – the broadened main lines should not overlap with one another. The radiated intensity distribution in a single line could be determined more accurately by deconvoluting a “real”, higher-resolution line profile from the instrumentally broadened line profile for all points along the line. This “real” line profile (that

includes the plasma-related line broadening) could be obtained with a higher-resolution spectrometer.

To provide a higher resolution spectrum, a curved crystal spectrometer was developed. It is a cylindrically bent concave KAP crystal spectrometer based on the Johann geometry11, in which the focusing minimizes the broadening from the finite source size, with a 5-10Å range covering the whole Al-Mg K-shell spectrum. The calculated spectral resolving power of the spectrometer is over λ/Δλ~1000.

The first experiments with the spectrometers were completed in September 2013. Preliminary results were not ready to be included in this draft, but will be available by the time of the DOE Review.

This postdoctoral research work is

conducted under the supervision of Dr. Radu Presura. [1] S. A. Pikuz et al., JETP Letters 61, 638 (1995) [2] Ye. Aglitskiy et al., Appl. Opt. 37, 5253 (1998) [3] D. B. Sinars et al., Appl. Opt. 42, 4060 (2003) [4] J. A. Koch et al., Rev. Sci. Instr. 76, 073708 (2005) [5] L.A. Welser et al., Rev. Sci. Instr. 77, 10E320 (2006) [6] M. de Broglie et al., Compt. Rend. Acad. Sci. 158, 944 (1914) [7] M. Swartz et al., J. Phys. B 4, 1747 (1971) [8] D. Papp et al., Proc. IEEE. Conf. PPPS 2013 (in press) [9] B.L. Henke et al., Atomic Data and Nuclear Data Tables 54, 181 (1993) [10] J.J. MacFarlane et al., Proc. 3rd Int. Conf. on Inertial Fusion Sciences and Appl., 457 (2004) [11] H. H. Johann, Z. Phys. 69, 185 (1931)

37

Focusing of an Explosive Plasma Expansion in a Transverse Magnetic Field

R. Presura1, C. Plechaty2, A. A. Esaulov1, S. Haque1, S. Stein3, L. O’Brien4, M. Tooth1,

D. Martinez2

(1) University of Nevada, Reno, MS 220, Reno, Nevada 89557-0058, United States (2) currently at Lawrence Livermore National Laboratory, Livermore CA 94550, United States

(3) currently at Raytheon Missile Systems, Tucson, AZ, United States (4) currently at University of Colorado, Boulder, Boulder CO, United States

Award Number: DE-FC52-06NA27616

The dynamics of a laser ablation plasma expanding in an external magnetic field have been investigated with imaging interferometry and shadowgraphy. The diagnostics reveal a new interaction mechanism, namely the redirection of the explosive plasma expansion into a converging flow. Comparison with 3D ideal magnetohydrodynamic simulation results supports the observation that the efficient lateral plasma confinement causes the plasma to converge on-axis and initiate a directed flow. The resulting collimated flow propagates across the magnetic field in a kinetic regime, which cannot be modeled within the same framework.

The experiments were performed at the Nevada Terawatt Facility using the terawatt Leopard laser to generate ablation plasmas in the magnetic field produced by Zebra.

Fig. 1. Experimental Setup. J is the current density vector and B is the magnetic field vector. Coordinate system: the y axis is perpendicular to the target surface and points toward the electrode along the magnetic field gradient, the z axis is anti-parallel to J, and the x axis is the laser probe propagation direction. The origin is located in the center of the focal spot on the target surface.

The experimental set-up shown in Fig. 1 includes refractometric diagnostics used to characterize the plasma evolution.

To assist in the understanding of the plasma dynamics in an external magnetic field, numerical modeling was performed with AW-MHD [1], a 3D ideal MHD code. The simulation results agree well with the experimental observations of the plasma expansion both with and without an external magnetic field, and provide parameters inaccessible experimentally.

Fig. 2. Plasma Expansion for B = 0, characterized by (a-b) linear plasma density nl reconstructed from interferograms and (c-d) shadowgraphy. Images are taken for the following expansion times: (a) and (c) at t ≈ 3.7 ns, (b) and (d) at t ≈ 9.5 ns. Images (a) and (b) use the color scale shown (in units of 1018 cm-3 mm) with isodensity contours drawn for clarity; in the white regions the fringe shift could not be determined due to insuffcient nl, refraction, or absorption of the probing beam.

The plasma plume preferentially expanding along the target normal in the absence of a magnetic field is confined laterally and turns into a directed plasma flow when a field is applied. The lateral

38

confinement leads to a redirection of the interior plasma originating from the target region heated by the ablation laser. The redirection mechanism is similar to that proposed in Ref. [2], with the difference that in our experiment, the magnetic field provides the external pressure profile required for the guidance of the explosive plasma flow. This pressure redirects the flow toward the axis, and this convergence generates a directed flow, as discussed in Ref. [3]. Diffusion of the magnetic field into the directed flow allows the flow to self-polarize with a field Ep. The flow then penetrates the magnetic field due to Ep x B drift.

Fig. 3. Plasma expansion in external magnetic field represented by the line-integrated plasma density nl, using the color scale of Fig. 2. Each image was obtained in a different shot. The magnetic field vector points into the page and its amplitude varies within less than 10% for the expansion times shown.

Fig. 4. AW-MHD results for ne in the y-z plane for (a)-(b) B = 0 and (c)-(e) B ≠ 0. In (a)-(e), arrows denote the direction of the plasma velocity vector in the plane of the image. (f)-(h) AW-MHD results for the magnitude of the magnetic field in the same plane.

In summary, a previously

unexplored type of interaction between a laser-produced plasma flow and a magnetic field was identified and investigated.

The authors would like to thank Dr. Gennady Sarkisov for designing the interferometry and shadow diagnostics. [1] A. A. Esaulov, V. L. Kantsyrev, A. S. Safronova, A. L. Velikovich, M. E. Cuneo, B. Jones,K. W. Struve, and T. A. Mehlhorn, Physics of Plasmas 15, 052703 (2008) [2] A. Frank, B. Balick, and M. Livio, The Astrophysical Journal 471, L53 (1996). [3] J. Canto, G. Tenorio-Tagle, and M. Rozyczka, Astronomy and Astrophysics 192, 287 (1988).

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Staged Z-Pinch Implosions to Produce High-Energy-Density Plasma

R. Presura1, H. U. Rahman2, F. J. Wessel2, P. Ney3

(1) University of Nevada, Reno, MS220, Reno, Nevada 89557-0058, United States (2) University of California, Irvine, Irvine CA 92697, United States (3) Mount San Jacinto College, Menifee CA 92584, United States

Award Number(s): DE-FC52-06NA27616 and DE-NA0002075

A Z-pinch liner, imploding onto a target plasma, evolves in a step-wise manner, producing a stable, magneto-inertial, high-energy-density plasma compression. [1]. The typical configuration is a cylindrical, high-atomic-number liner imploding onto a low-atomic-number target, as shown in Fig. 1.

Fig. 1. Staged Z-pinch. [1]

The parameters for the Zebra terawatt-class machine have been simulated by the California collaborators using the 2-1/2 D MHD code, MACH2. An initial radius of a few mm is required for stable implosion; the material densities properly distributed so that the target is effectively heated initially by shock heating and finally by adiabatic compression; and the liner's thickness adjusted to promote radial current transport and subsequent amplification in the target. Since the shock velocity is smaller in the liner than in the target, a stable shock forms at the interface, allowing the central load to accelerate magnetically and inertially, producing a magneto-inertial implosion and high-energy-density plasma, as shown in Fig. 2.

Fig. 2. Plasma density (in cm-3, top) and temperature (in eV, bottom) for a silver liner imploding on a hydrogen fill plasma at peak compression time. The abscissa represents the radius in cm. [1]

Comparing the implosion dynamics of a low-Z target with those of a high-Z target (a summary of parameters is given in Table 1 [1]), demonstrates the role of shock waves in terms of compression and heating. In the case of a high-Z target, the shock

40

wave does not play a significant heating role. The shock waves carry current and transport the magnetic field, producing a high density on-axis, at relatively low temperature. Whereas, in the case of a low-Z target, the fast moving shock wave preheats the target during the initial implosion phase and the later adiabatic compression further heats the target to very high energy density. As a result, the compression ratio required for heating the low-Z plasma to very high energy densities is greatly reduced.

In simulations, the plasma was

driven self-consistently using a Thevenin equivalent circuit for Zebra.

Experiments were performed to drive loads with parameters in the range predicted optimal by simulations, namely several-mm diameter liners with micron-thick walls. These included machined Al tubes, rolled foils supported inside insulating tubes, and thin metal layers deposited on the inner surface of insulating tubes. The self-standing metal tubes were too heavy to compress with Zebra. When using structures with insulating tubes, the current flow could be confined to the metal liner for only 25-50% of the maximum intensity, after which the electric field became strong enough to break down (electrically) the other surface of the insulator and the current switched to that lower inductance path. While some work is being done to improve the design of

the insulators, currently we are working on the implementation of a double coaxial gas puff structure that can meet the requirements for staged Z-pinch heating without the difficulties related to surface flashover. [1] H. U. Rahman, F. J. Wessel, P. Ney, R. Presura, R. Ellahi, P. K. Shukla, Phys. Plasmas 19, 122701 (2012).

41

Kelvin-Helmholtz Instabilities Generated in Magnetized High-Energy-Density Plasma

R. Presura1, S. Stein2, D. Martinez3, S. Haque1, L. O’Brien4

(1) University of Nevada, Reno, MS 220, Reno, Nevada 89557-0058, United States (2) currently at Raytheon Missile Systems, Tucson, AZ, United States

(3) currently at Lawrence Livermore National Laboratory, Livermore CA 94550, United States (4) currently at University of Colorado, Boulder, Boulder CO, United States


Supersonic plasma flows were produced on the NTF’s Zebra pulsed-power generator to investigate the stabilization of Z-pinches by shear flows [1, 2]. Conical wire arrays [3, 4] driven at 1 MA were used to generate plasma flows. To introduce a radial profile in the axial velocity (the shear), an additional wire was placed on the axis of the array. Assuming the flow, otherwise considered uniform, entirely stops at contact with the wire, this configuration is expected to produce a quasi-parabolic velocity profile [5]. Initial experimental results qualitatively showed improved Z-pinch stability, in particular notable mitigation of the m = 1 instability [6].

Fig. 1. Kelvin-Helmholtz Vortices Created by Shear Flow in a Conical Wire Array (in the center of this laser shadow image). Visible are the ablated wires of the array and plasma streaming from them towards the axis of the array. [7] The width of the image is 8 mm.

The ability to produce shear flows creates an experimental platform for the investigation of Kelvin-Helmholtz instabilities (KHI) in magnetized plasmas.

This instability was observed in the conical wire array configuration (Fig. 1) [7]. To simplify the geometry and to obtain better diagnostic access to the instability formation region, a “wedge” wire array configuration was developed, with a quasi-two-dimensional geometry [8]. Two planar wire arrays tilted at equal angles with respect to the symmetry plane of the array were used to generate the plasma flow, similar to the conical wire array. The shear was introduced by the interaction of the flows with a thin foil placed in the symmetry plane. The planar arrays were usually over-massed for Zebra to maintain steady plasma flow without changing the geometry. Each planar array can consist of materials with different atomic numbers to assess the importance of radiative losses upon the growth of the KHI in magnetized plasmas. The current through the central foil can be varied to change the characteristics of the ablation plasma, and therefore of the conditions for KHI development. An example of result is shown in Fig. 2. This configuration enables the laboratory simulation of natural instances such as the penetration of the solar wind in the Earth’s magnetotail [9]. With addition of an external magnetic field, it may be used to verify theoretical and computational results (e.g. [10]) regarding its stabilizing effect upon the KHI growth.

42

Fig. 2. Kelvin-Helmholtz Instability Produced with a Wedge Wire Array (only one half of the array is shown in this laser shadow image). The right edge of the image shows plasma ablated from the central foil. The sharp feature parallel to the plasma edge is the shock produced when the plasma flow from the wires impacts it, and where the flow is redirected in axial direction. The instability forms within the plasma ablated from the foil between the shock and the foil. The oblique shadow at the left of the image represents the plasma ablated from the planar wire array. This image is 6 mm wide.

[1] T. D. Arber and D. F. Howell, Phys. Plasmas 3, 554-560 (1995). [2] U. Shumlak and C. W. Hartman, Phys. Rev. Lett. 75, 3285-3288 (1995). [3] S. V. Lebedev, J. P. Chittenden, F. N. Beg, S. N. Bland, A. Ciardi, D. Ampleford, S. Hughes, M. G. Haines, A. Frank, E. G. Blackman, and T. Gardiner, Astrophys. J. 564, 113-119 (2002). [4] D. J. Ampleford, S. V. Lebedev, S. N. Bland, S. C. Bott, J. P. Chittenden, C. A. Jennings, V. L. Kantsyrev, A. S. Safronova, V. V. Ivanov, D. A. Fedin, P. J. Laca, M. F. Yilmaz, V. Nalajala, I. Shrestha, K. Williamson, G. Osborne, A. Haboub, and A. Ciardi, Phys. Plasmas 14, 102704 (2007). [5] L. F. Wanex, Astrophys Space Sci. 298, 337 (2005). [6] D. Martinez, R. Presura. S. Stein, C. Plechaty, S. Neff, High Energy Density Physics 6, 237-241 (2010). [7] D. Martinez, R. Presura, S. Wright, C. Plechaty, S. Neff, L. Wanex, D. Ampleford, Astrophys. Space Sci. 322, 205-208 (2009). [8] R. Presura, S. Stein, D. Martinez, S. Haque, L. O’Brien, Bull. Am. Phys. Soc. 55 (2010), http://meetings.aps.org/link/BAPS.2010.DPP.CP9.87. [9] H. Hasegawa, M. Fujimoto, T.-D. Phan, Nature, 430, 755-758 (2004). [10] D. Ryu, T. W. Jones, A. Frank, Astrophys. J. 545, 475-493 (2000).

43

Electron Energy Characterization of Electron Beams in Z-Pinch Plasmas Using Magnetic Deflection

M.S. Wallace, R. Presura, S. Haque, A. Arias, N. Quiros

Nevada Terawatt Facility, Department of Physics, University of Nevada, Reno,

Reno Nevada 89557-0058, United States Award Number: DE-NA-00001834, DE-FC52-06NA27616, DE-NA0002075

The presence of energetic electron beams in wire array Z-pinch plasmas has been often noted in the past. These energetic electron beams have been inferred from the observation of hard x-ray bursts during these pinches [1-3]. Direct measurements of the beam energies and currents have also been attempted by use of a Faraday cup and by analyzing anode damage [4] thought to be caused by such beams. The mechanisms leading to the production of these energetic electron beams are still not well-understood.

For a more precise characterization of the electron beams produced in Z-pinches, electron energies and beam currents were measured by coupling magnetic deflection with Faraday cup collection. The electron beams were collimated with a pinhole placed on the pinch axis. After passing through the pinhole, the electrons were dispersed angularly according to their energy by magnetic deflection. Multiple Faraday cups placed at different angles above the magnet were used to collect the electrons, to provide time-resolved current measurements for several electron energy ranges. The set-up is shown in Fig. 1.

Under the assumption of a uniform magnetic field and knowing the size of the magnet, one can calculate (Fig. 2) the radius, R, of the curved path the electrons will follow, the distance, x, the electrons will be displaced from the pinch axis when they exit the magnet, and their exit angle, α, for any electron energy.

For the magnet used (B ≈ 0.08 T) and the given cup openings (φ ≈ 5 mm), the following table gives the energy ranges for the cup positions used during measurements:

Angle (°) 20 43.5 50 64.5 79 Emin(keV) 89.4 140 172 324 916 Emax(keV) 93.7 153 191 386 1140

This type of magnetic spectrometry was carried out for a variety of wire-array configurations driven by the 1 MA Z-pinch Zebra at the Nevada Terawatt Facility. The study included cylindrical arrays, conical

44

arrays, inverse conical arrays, and X-pinches. All arrays were built with eight 15 μm Al wires, with load diameters close to those required for optimum pinch time on Zebra. The X-pinches consisted of four Al wires, with mass comparable to that of the arrays. The following panels show results representative for each of these configurations. In the legend entries, FC x-α°, α is the magnet exit angle of the electrons entering Faraday cup x on its axis.

Two tests were performed to verify the significance of these results. Faraday cups placed at the same angles in the direction of positive deflection did not yield any signals simultaneous with those of the electron measuring cups. In the absence of the magnet, the pairs of cups placed at the same angle produced similar signals.

Each wire-array style leads to a different electron beam signature in time, in the total charge the beam carries, and in the energy of the electrons in the beam. For the cylindrical loads the least energetic electron beams were observed. In shot 3024 the Faraday cup placed at 15° (electron energies in the range 86±2 keV) collected a charge of about -4×10-10 C; the cup placed at 50° collected a charge of -1.6×10-11 C; and the highest energy cup (placed at 79°) collected -1.9×10-11 C. For X-pinches, the most energetic electron beams are produced and in much larger amounts. In shot 3019, the Faraday cup placed at 20° collected a charge of -1E×10-9 C; the cup at 43.5° collected a charge of -9.4×10-10 C; the cup at 64.5° collected a charge of -1.5×10-10 C; and the highest energy cup collected -2.8×10-10 C. It is not entirely surprising that the highest-energy cup collected an overall higher amount of charge than the second highest energy-level cup because of the larger range this cup was observing. However, more analysis and complementary measurements are needed to start deciphering the mechanism accelerating the energetic electron beams observed in Z-pinch plasmas. [1] F. N. Beg, A. E. Dangor, P. Lee, M. Tatarakis, S. L. Niffikeer, M. G. Haines, Plasma Phys. Control. Fusion 39 (1997) 1. [2] V. L. Kansyrev et al., Rev. Sci. Instrum. 75 (2004) 3708. [3] I. Shrestha et al., IEEE Trans. Plasma Sci. 38 (2010) 658. [4] V. L. Kantsyrev et al., IEEE Trans. Plasma Sci. 34 (2006) 194.

45

Resistive Guiding of Laser-driven Fast Electrons in Solids

P. Leblanc and Y. Sentoku

Nevada Terawatt Facility, Department of Physics, University of Nevada, Reno, MS 220

Reno, Nevada 89557-0058, United States

Award Number(s): DE-FC02-04ER54789, DE-SC0008827, DE-FG52-09NA29554, DE-FC52-06NA27616, DE-NA0002075

Ultrahigh currents of supra-thermal electrons that are driven through solids using relativistic laser pulses (with intensity I > 1018 W/cm2), lie at the heart of numerous applications such as the generation of ultra-short secondary sources of particles and ra-diation (ions, x-rays, positrons, or neutrons), fast ignition of inertial confinement targets, or laser-driven hadron therapy. The study of electron transport in high-energy-density (HED) plasmas has been a critical area of focus to develop these applications. A num-ber of experimental studies have been car-ried out in the past to characterize electron transport in different media such as insula-tors, metals, and compressed matter. To date however, the physics of HED plasmas, espe-cially the energy transport in resistive tar-gets, is not fully understood due to the wide range of plasma phenomena ranging from the kinetic regime to the collisional regime including complex atomics processes such as ionization and radiation.

Prior work in the field of the study of electron transport done by Stephens et al [1] on the comparison of transport features be-tween conductors and insulators has yielded interesting results. Measurements of Kα emissions from a fluorescing copper layer embedded inside a target as a result of high-intensity laser interactions, have shown two distinct images when a different transport medium is used. The aluminum target dis-played a single peak in the Kα images in-dicative of a tightly collimated electron beam while the plastic's Kα signal was broader with multiple peaks indicating a non-uniform density in the electron transport current, shown in Fig.1 (i) and (j).

In this work we perform a series of simulations of transport in plastic (CH),

aluminum, and silicon to attempt to explain these differences.

We use a two-dimensional collisional particle-in-cell code, PICLS [2,3], which features binary collisions among charged particles and dynamic ionization processes in gas and solid density plasmas. The simu-lation parameters were determined in ac-cordance with the experimental conditions of Ref. [1]. Two simulations were prepared with targets made of solid plastic and alumi-num to represent insulators and conductors to study the materials specific to the experi-ment. Since plastic and aluminum have dif-ferent average atomic numbers Z, solid sili-con was chosen as a third material to repre-sent an insulator with similar atomic number Z to aluminum to see the effect of initial in-sulation on transport physics.

A 20 µm thick pre-plasma is placed in front of the target and is given an exponen-tially increasing density profile with a short scale length of 2 µm and a maximum densi-ty of 100nc. For all materials, the pre-plasma is composed of aluminum for the laser ab-sorption to be identical for each simulation. The 145µm deep by 150 µm wide target is placed in a 200 by 150 µm simulation box with 5 µm of vacuum in front of the target. An 800 fs laser pulse is injected from the left boundary at an intensity of 1019 W/cm2 with a wavelength of 1µm. The beam is fo-cused down to 10 µm corresponding to the full width at half the maximum intensity and the rise time is 100 fs. Both field ionization and collisional ionization are included along with binary collision among charges in par-tially ionized plasmas [3]. The plastic and aluminum targets are given an initial charge state of Z=0 and Z=3 in order to distinguish them as insulator and conductor respective-ly.

46

Fig. 1 (a-c) and (d-f) show the time evolution of electron energy density in alu-minum and plastic targets, respectively. Fast electrons inside the aluminum appear to form a narrow jet along the center of the target with the majority of electrons being confined by the strong magnetic field to re-side in a narrow (~ 50 µm) wide stream. This geometry is temporally and spatially stable as is evidenced by the jet maintaining collimation over the entire thickness of the target and at later times until the pulse is turned off. On the other hand, the plastic target reveals that energetic electrons are broken into multiple channels. The time in-tegrated electron flux of forward moving electrons is obtained at 125µm from the tar-get and shown in Fig.1 (g) for Al and (j) for plastic. These figures relate to the Kα imag-es observed at the same location in experi-ment [7] shown in Fig.1 (i) and (j) by the fact that Kα emissions are proportional to the number of hot electrons (above keV) which pass through the copper layer located 125µm inside the target. We see a similar trend in the Kα images in the simulation results, namely, one single narrow image for Al and a widely-spread, multi-peak image for the plastic. Note here that for early time (Fig.1 (a) and (d) at t=250fs), both Al and plastic exhibit a similar transport pattern, which indicates the magnetic field in Al is not yet strong enough to squeeze the elec-tron flux at this moment.

To understand the physics behind the instability, a simulation with an insulator with a Z value comparable to aluminum was performed in order to have similar resistivi-ty. Fig.1 (k) shows the resulting electron energy density inside a silicon target which exhibits the same behavior as aluminum. Based on this fact the resistivity of the mate-rial appears to dominate transport while the initial electrical properties of the material do not appear to affect the transport pattern once the energy deposition achieves a steady state.

It is crucial to control the fast-electron transport in dense plasmas to design applica-tions. We have performed two-dimensional

PICLS simulations with collisions and ioni-zations. The results are consistent with the previous experimental data, which indicates the collimation observed in the aluminum target occurs when the fast electrons are guided by the resistive magnetic fields ap-pearing inside the target after certain time later.

Fig.1. 2D Contour Plots of the Normalized Elec-tron Energy Density for (a-c) aluminum, and (d-f) plastic at t=250, 500, 1000fs. A white bar in each plot indicates 50µm scale. The time inte-grated flux of forward going hot electrons over 2ps at 125µm deep inside the target for (g) alu-minum and (h) plastic. Kα images taken at 125µm inside the target for (i) aluminum and (j) plastic from Ref.[1]. (k) The electron energy density for silicon at 500fs. [1] R. B. Stephens et al, Phys. Rev. E 69,

066414 (2004). [2] Y. Sentoku, and A. J. Kemp, J. Comput.

Phys. 227, 6846 (2008). [3] R. Mishra, P. Leblanc, Y. Sentoku et al.,

Phy. Plasmas 20, 072704 (2013).

47

Higher-order Terms of Radiative Damping in Extreme Intense Laser-matter Interaction

R. Pandit and Y. Sentoku



Award Number(s): DE-FC02-04ER54789 and DE-FC52-06NA27616

With the advent of high-powered, short-pulse lasers, it becomes possible to extend laser intensities to 1021 W/cm2. In a few years, the intensity on target will exceed 1023 W/cm2, and electrons accelerated by such an intense laser field will reach ener-gies beyond 100 MeV and start to strongly emit radiation. Then the radiation loss from an accelerated electron will no longer be negligible and will affect its motion (so-called radiative damping).

To study the effects of radiative damping, a code was developed to solve a set of equations describing the evolution of a strong electromagnetic wave interacting with a single electron. Usually the equation of motion of an electron including radiative damping under the influence of electromag-netic fields is derived from the Lorentz-Abraham-Dirac (LAD) equation treating the damping as a perturbation [1]. The 1st-order correction of the Lorentz-Abraham-Dirac (LAD) equation is known as the Landau-Lifshitz (LL) equation. Until now, only the first-order damping equation of the LAD equation has been used [2]. The 2nd-order terms are thought to be small in comparison with the 1st-order terms. For single-particle calculations, (Ref. [3]), the LAD equation was numerically solved for the stationary solution and in Ref. [4] it was numerically solved backward in time. In both references it is found that there are small deviations in the LAD and LL equations in the classical regime for single particles. However, since small deviations might be enhanced by col-lective effects in laser-plasma interactions, the LL equation alone might not be suffi-cient to describe the motion of particles in the classical regime. Therefore, we have derived all terms up to the 2nd-order terms,

and have tested them by implementing them in a laser-plasma simulation code.

The radiative damping effect is as-cribed to relativistic electron beams. It is usually negligible in over-dense plasmas where the laser fields are usually weak, while in under-dense plasmas it is important because electrons are directly accelerated by the strong fields. The amount of energy emitted as radiation is negligible in the non-relativistic regime (<1018W/cm2), but not in the strong relativistic regime. Relativistical-ly, the equation of motion of the radiating electron is written in the following form,

Here the 1st-order term g1 is given by re-expressing the four dimensional form with the fields as

We write here only the largest term in the complex terms. This is a kind of friction force, which slows down the electron. Simi-larly we also have derived the 2nd-order term. The following is the largest terms (γ4) in the 2nd-order terms,

This is the damping of the Lorentz force in the radiative process. In this equation, the higher order term is smaller than the previ-ous order term by a factor of the classical electron radius re =e2/mc2 ~ 10-13 such that

48

the 2nd-order term was previously thought to be negligible in comparison with the 1st-order term.

We have implemented the 1st-order term and the 2nd-order damping term in the Particle-in-Cell (PIC) code in order to study radiation effects in the super-intense laser - matter interaction for extreme intensity, I> 1022 W/cm2. The numerical code used is the one- & two-dimensional (PIC) code PICLS, which features binary collisions between charged particles and ionization processes in gaseous and solid density plasmas. We have implemented the friction force (1st-order) and the damping of the Lorentz force (2nd-order) equations within the leap-frog (time-centered) scheme to integrate the kinetic equation. The friction (1st-order) is taken into account at the centered time, and damp-ing of the Lorentz force (2nd-order) is simply done by reducing the Lorentz force by a fac-tor calculated by the equation.

The target is modeled as a 5µm thick solid copper slab with uniform density. A few micron thick pre-plasma is placed in front of the target. The ion density is set to 50nc, here nc=1021cm-3 is the critical density for a laser wavelength 1µm. Initially we set the ion charge state at Z=3, and electron density is set to neutralize the ion charges.

1-D simulations were performed to see the effect of radiative damping by the 1st-order term alone, and then by the 1st+ 2nd-order terms where we specifically looked at electron and ion phase space, energy spec-trum and energy density. The laser intensity is 1023 W/cm2 and the pulse duration is 100 fs.

Fig. 1 (a) shows the phase plot of the ions and (b) energy spectrum of electrons with and without radiative damping at the time when the pulse is reflected from the target surface. Strong damping of high en-ergy electrons (px/mec > 1000) in the elec-tron spectrum plots are observed at this time. The 2nd-order damping term reduces more energy than the 1st-order term only.

Fig. 1 (a) shows the phase plot of ions of the same laser intensity at the same time with the electron spectrum. The interface speed, which is determined by the photon

pressure, is clearly seen to be slower in the case with 2nd-order damping as compared to the one with the 1st-order term alone. As we discussed in the previous section, the 2nd-order term reduces the Lorentz force, includ-ing the JxB force, so that the effective pho-ton pressure decreases at the absorption point. This result indicates that the 2nd-order term is important in the discussion of ion acceleration by the photon pressure with a laser intensity >1023 W/cm2.

Fig.1. 1D-PIC result with I=1023W/cm2: (a) Lon-gitudinal phase of ions at t = 181.5 fs when the pulse peak hits the target. (b) The electron spec-trum observed at the same time of (a). [1] L.D. Landau and E.M. Lifshits, The

Classical Theory of Fields (Pergamon, New York, 1994).

[2] A. Zhidkov, J. Koga, A. Sasaki, M. Uesaka, Phys. Rev. Lett. 88, 185002 (2002).

[3] S. V. Bulanov, T. Zh. Esirkepov, M. Kando, J. K. Koga, S. S. Bulanov, Phys. Rev. E 84, 056605 (2011)

[4] J. Koga, Phys. Rev. E 70, 046502 (2004).

49

Radiation Transport in Ultrafast Heated High-Z Solid Targets

I.Paraschiv1, Y. Sentoku1, R. Mancini1, T. Johzaki2

(1) Nevada Terawatt Facility, Department of Physics, University of Nevada, Reno, MS 220 Reno, Nevada 89557-0058, United States

(2)Hiroshima University, Japan

Award Numbers: DE-SC0008827, DE-FC52-06NA27616, DE-NA0002075,

Intense laser-target interactions generate hot, dense, radiating plasmas and for high-Z target materials, radiation effects become one of the important energy-exchange mechanisms. In order to assess the cooling and heating effects due to the radiation field in a laser-produced plasma, one has to take into account the transport of radiation as it travels through the heated material. For this purpose we are developing a radiation transport model coupled with our PICLS code for the purpose of evaluating the effect of radiation in the plasma development.

Radiation transport has been implemented both in the 1D PICLS code and in the 2D PICLS code. Two different numerical schemes have been used for the two versions of the PIC code to benchmark the algorithm’s performance.

In solving the equation of radiation transfer it was assumed that opacities and emissivities were known in all the grid points. The code uses a database of emissivities and opacities as functions of photon frequency, created for given densities and temperatures by the non-equilibrium, collisional-radiative atomic kinetics 0-D code FLYCHK together with its postprocessor FLYSPECTRA [1]. The postprocessor FLYSPECTRA synthesizes the emission and absorption spectra, by computing the emissivity and opacity using the population distribution from the FLYCHK output file.

Data obtained from FLYCHCK is averaged so that an input database is generated. We have generated data over a spectral energy range from 1 eV to 10 keV averaged over 100 energy groups.

The radiation transport module solves the radiative transfer equation:

(1) ( ) ( )

( ) ( )

1 , , , , , ,

, , , , , , ,

I t tc t

t I t

ν η ν

χ ν ν

∂ + ⋅∇ = − ∂ −

n x n x n

x n x n

where I is the specific intensity of radiation, χ is the opacity, η is the emissivity, n is the unit vector along of direction of radiation propagation, x is the spatial coordinate, and ν is the photon frequency. The equation of radiation transfer is directly integrated to yield the intensity I, which in turn is used to compute the net radiation emission energy density (ER) in each grid cell. If ER > 0, the plasma is cooling and the bulk electrons will lose energy. If ER < 0 then plasma is being heated by radiation, and the bulk electrons will gain energy. The self-consistent coupling of the radiation transport module with the PICLS code is illustrated in Fig. 1.

Fig. 1. Coupling of the Radiation Transport Module with the PICLS Code.

For the 1D version we have implemented an attenuation operator solver short-characteristics numerical scheme [2,3] to solve the 1D steady-state radiation transport equation. Fig. 2 shows results obtained by the PICLS 1D radiative code for the electron temperature inside a 5 µm Cu target irradiated by a laser of 1019 W/cm2 intensity, 1 µm wavelength, and with a ramped pulse of 165 fs rise time and 990 fs

50

constant ramp. The results show a hotter target at the front but becoming colder on the inside when compared with the results obtained when the radiation effects are neglected.

0.0E+00

5.0E+02

1.0E+03

1.5E+03

2.0E+03

2.5E+03

17.5 18.5 19.5 20.5 21.5 22.5 23.5

Te (e

V)

x (µm)

Electron temperature inside the target (5 µm Cu) at t=0.5 ps

Without radiation transport

With radiation transport

Fig. 2. Electron Temperature Inside a 5 µm Cu Target Irradiated by a Laser of 1019 W/cm2 Intensity and 1 µm Wavelength.

The 2D PIC version was developed

by modifying the neutron transport code described in Ref. [4], and improved by adapting the cubic interpolation (CIP) scheme to solve the advection terms in the radiation transport equation. To show the capability of the RT-PIC simulation, we perform a 2D simulation for a copper target heated by an intense laser pulse (I=1020

W/cm2, spot size=10 µm, duration=300 fs). Fig. 3 shows the radiation energy

distribution observed at 465 fs after the pulse irradiation. The blue-green areas are the areas in which the plasma lost energy by emitting x-rays (ER>0), while the plasma gained energy by absorbing x-rays in the orange-red areas (ER <0).

The x-ray spectrum observed inside the copper target is shown in Fig. 4 at two times: 150 fs and 300 fs. We see that as the target gets heated, the high energy photons around 8-9 keV become significant.

Fig. 3. The Net Power Distribution of X-ray Radiation.

Fig. 4. The Spectrum Observed at the Heated Area Inside the Copper Target. References [1] H.-K. Chung, M.H. Chen, W.L. Morgan, Y. Ralchenko, HEDP 1, 3 (2005) [2] P. Kunasz and L.H. Auer, J. Quant. Spectrosc. Radiat. Transfer 39, 67 (1988). [3] M. van Noort, I. Hubeny and T. Lanz, ApJ 568, 1066 (2002) [4] C.E. Lee, Los Alamos Scientific Laboratory Report LA-2595 (1962) [5] F. Xiao, T. Yabe, G. Nizam, T. Ito, Comput. Phys. Commun. 94, 103 (1996)

51

Proton Deflectometry for Investigation of Magnetic Field Configuration in Pulsed-power-driven systems

D. Mariscal1, C. McGuffey1, J. Valenzuela1, M.S. Wei1,4, F.N. Beg1, R. Presura2, A.

Covington2, D. Papp2, M. Wallace2, S. Haque2, A. Arias2, B. Largent2, H. Sawada2, J.P. Chittenden3

(1)University of California San Diego, La Jolla CA 92093, United States (2)Nevada Terawatt Facility, Department of Physics, University of Nevada, Reno,

Reno NV 89557-0058, United States (3)Imperial College, London SW7 2BZ, United Kingdom

(4) General Atomics, San Diego, CA 92121, United States Award Number(s): DE-SC-0001992, NSF-PHY-0903876

Proton radiography has been widely used as a method of assessing the magnitude and structure of electromagnetic fields generated in laser-plasma interaction experiments. The implementation of this technique in pulsed-power-produced plasma experiments is crucial to verifying theory and answering long-standing questions about electromagnetic field topology. Measurements of the field topology through other means have proven unreliable and limited in scope. For example, electrical probes can fail on-shot due to MV potentials, and optical Faraday rotation is limited to areas wherein the density of the plasma is below the critical density and free of strong gradients. Proton deflectometry has the potential to overcome these restraints and offers a means of recovering magnetic field measurements in dense plasma regions which were previously inaccessible.

Experiments were performed by coupling the NTF’s mega-ampere generator, Zebra, to its terawatt short-pulse laser, Leopard. Zebra was operated in long-pulse mode, delivering a maximum 0.6 MA current with a rise time of approximately 200 ns. In short-pulse mode, Leopard delivered ~12-15 J, in ~300 fs, at a 1.054 µm wavelength, which was focused to a spot size diameter of ~7.5 µm, giving an on-target intensity of > 1019 W cm-2. Targets were ~1.5 mm x 1.5 mm, 2 µm Ti foils. A ~20 µm thick Cu mesh was placed ~1-2 mm

from the rear surface of the target in order to imprint the proton beam with a gridded structure to make distortions due to encountered electromagnetic fields quantifiable. Protons were detected with multiple layers of radiochromic film, RCF, which was wrapped in Al foil. The general experimental geometry is shown in Fig. 1. The 3D resistive MHD code, Gorgon was used to simulate z-pinch loads. Simulated proton probing through the Z-pinch system was accomplished by using either the 3D hybrid PIC Large-Scale Plasma code, or Gorgon’s proton-probing, post-processor with the results compared against the experimental data1-2.

Fig. 1. Schematic of the experimental set up for proton deflectometry of short circuits.

52

The first tests of the method utilized a

6 mm diameter short-circuit load, resulting in a maximum calculated magnetic field at the surface of the conductor of ~ 40 T. Using such a load eliminates many of the issues associated with the application of this method to plasma loads, primarily the problem of high-velocity debris, which has the potential to damage both the optical components and the RCF detector. The resulting set-up provides a simple test bed for both the experiment and simulation before applying the method to plasma loads. Some of the results from these tests are shown in Fig. 2. For the experimental set-up shown, the radial probing geometry, with the proton beam incident from the radial direction with respect to the z-axis of the short-circuit, protons are expected to be deflected radially away from the load, as well as vertically upward. The relative angle between the two resulting features then

increases as the load current is increased. The proton deflectometry method was then applied to radial foil loads, which have been studied extensively for their complex magnetic field configurations and similarities to astrophysical phenomena4. In this set-up, a radial foil is stretched between the outer electrode while a 3 mm diameter cathode contacts below the surface of the foil, producing a JxB force directed upward. An example of the data is shown in Fig. 3, in which protons have been deflected away from the current-carrying and field region, which in turn, has moved away from the surface of the foil.

Proton deflectometry has been demonstrated for the first time on short-circuit loads, as well as in Z-pinch loads at the mega-ampere scale. In addition to the data presented, plasma loads such as x- pinches, hybrid x-pinches, and cylindrical arrays have been examined. This method has already revealed details of the current and magnetic field configuration, which have yet to be fully understood. Further refinement in experimental technique as well as improvements to numerical methods will give insight into Z-pinch plasma phenomena which was previously inaccessible. The author would like to thank the NTF and its staff for the support of this work. [1] J.P. Chittenden et al., Phys. Plasmas 8, 2305 (2001) [2] http://www.lspsuite.com/ [3] M. Borghesi et al., Phys. Plasmas 9, 2214 (2002) [4] F. Suzuki-Vidal et al., Astrophys. Space Sci. 322, 19 (2009).

Fig. 2: (a) a proton beam with a mesh imprinted is sent through the short circuit load hardware with no Zebra current flowing. (b,c) Distorted proton beam with a mesh imprinted is deflected radially away from the vertical short-circuit.

Fig. 3. (a) Picture of setup for proton probing of radial foil generated plasma(b) RCF data showing dome shape from protons which are deflected out of field carrying region250 ns after current start. (c) Simulated RCF signal from Gorgon at the same time and location as in (b).

53

Experimental Studies of Implosion Characteristics and Radiation Properties of Planar and Cylindrical Wire Arrays

and X-pinches

V.L. Kantsyrev1, A.S. Safronova1, A.A. Esaulov1, I. K. Shrestha1, V.V. Shlyaptseva1, G.C. Osborne1,*, K.M. Williamson1,**, M.E. Weller1, A. Stafford1, S.F. Keim1, K. Schultz1, M.C. Cooper1, A.S. Chuvatin2, L.I. Rudakov3

(1)Department of Physics, University of Nevada, Reno, MS220 Reno, Nevada 89557, United States

(2) Ecole Polytechnique, 91128 Palaiseau, France (3)Icarus Research Inc., Bethesda, MD 20824, United States

*Present address: Naval Air Warfare Center, China Lake, CA 93555, United States **Present address: Sandia National Laboratories, Albuquerque, NM 87165, United States

Award Number(s): DE-FC52-06NA27586, DE-FC52-06NA27588, DE-NA0001984, DE-FC52-06NA27616, DE-NA0002075

In recent experiments, compact planar wire arrays (PWAs) demonstrated higher radiation yield, power, and plasma electron temperature in comparison with cylindrical wire arrays and X-pinches. New applications of PWAs to ICF and HEDP were shown. We continued these studies by proposing and then performing successful experiments with a new compact hohlraum design. We also performed experiments with relatively heavy X-pinches and single wires that focused on the study of the radiative properties of bright spots at higher currents of 1.7 MA. In addition, planar foil liners were investigated as another fruitful object for the study of dissipation mechanisms of magnetic energy in Z-pinch plasmas, as well as for alternative loads to wire arrays at multi-MA generators.

The purpose of this article is to show new results obtained during the years 2010-2013, and to express our interest in continuing these experiments on the NTF’s Zebra pulsed-power generator in the future. In general, pulsed-power facilities at universities, such as the one at the UNR, play an essential role in Z-pinch research through their mission of educating the next generation of HEDP scientists [1]. A relatively small Zebra generator allows graduate students hands-on experience in constructing, operating, modifying, and even repairing and running many types of plasma

diagnostics that can be very important for their future work at US National and Federal Laboratories.

The Zebra generator with Load Current Multiplier (LCM) can produce from 0.9 to 1.7 MA in ~100 ns at an electrical power of ~1.5 TW [2]. Zebra plasma diagnostics include the NTF core diagnostics: 1) two 5-channel-head x-ray power /yield diagnostics: bare bolometers, 5 µm kimfol XRD, 8 µm Be (or 7.5µm kapton) PCDs, 25 µm kapton PCD, EUV Si diode 0.15 µm Al filter; 2) time-integrated x-ray spectrometer axially resolved, 3) time-gated x-ray spectrometer, 4) time-gated x-ray pinhole camera, 5) laser shadowgraphy, optical streak camera, and ICCD, 6) Z-pinch current and voltage detectors. Additional diagnostics from our Plasma Physics and Diagnostics Laboratory (PPDL) have been used at Zebra: 1) time-gated EUV spectrometer, 2) time-integrated EUV spectrometer, 3) time-gated hard x-ray spectrometer, 4) time-integrated hard x-ray spectrometer axially resolved, 5) time-integrated pinhole camera, 6) 5-channel small head with hard x-ray/EUV diodes, 7) time-integrated x-ray polarimeter / spectrometer, 8) Faraday cup detectors and Thomson parabola analyzer. All time-gated diagnostics are synchronized on a master clock to provide an event-mode capability for the data acquisition system.

54

The Wire Ablation Dynamics Model (WADM) [3], non-LTE spectroscopic modeling [4], and VisRad code from Prism [5] were applied to analyze experimental data.

Our 2010-2013 experiments were focused on the continuation of current research, and also on new directions, such as the study of new hohlraum configurations with multiple planar wire array sources for inertial confinement fusion (ICF) [6-9] (Fig.1); the production of intense soft and hard x-rays from mono- and combined materials wire arrays and X-pinches including the study of anisotropy and x-ray pulse-shaping [6-12]; studies of the plasma dynamics of wire arrays, planar foils and X-pinch plasmas [9, 11-14]; the generation of electron beams from Z-pinch plasmas [15]; x-ray absorption spectroscopy of planar wire array plasma without an outer x-ray backlighter [16], as well as the investigation of dissipation mechanisms of magnetic energy in Z-pinch plasmas [6, 8, 9, 11, 14].

Fig. 1. Scheme of Experiments with a New Compact Hohlraum (28x12x10 mm) with Two Magnetically Decoupled W DPWA X-ray Sources Driving in Parallel. The experimental radiation temperature TR (40-50 eV) was in favorable agreement with the simulated value of TR ∼ 39 eV.

Some of this work constitutes the PhD dissertations of graduate students. Since October 2010, three graduate students have successfully graduated from our program(s) with a PhD.

Acknowledgments This work was supported by DOE/NNSA Cooperative Agreements DE-FC52-06NA27586, DE-FC52-06NA27588, and DE-NA0001984. It was in collaboration with A.L. Velikovich of the Naval Research Laboratory and M.E. Cuneo, B. Jones and R. Vesey of Sandia National Laboratories. The authors would like to thank the NTF technical staff for their efforts in conducting experiments on Zebra supported in part by DE-FC52-06NA27616 and DE-NA0002075. [1] J. Giuliani et al., IEEE Trans. Plasma Sci. 40 (2012) 3246. [2] A. S. Chuvatin et al., Phys. Rev. ST Accel. Beams 13 (2010) 010401. [3] A.A. Esaulov et al., High Energy Density Phys. 5 (2009) 166. [4] A. S. Safronova et al., High Energy Density Phys. 7 (2011) 252. [5] J. MacFarlane, J. Quant. Spectr. Rad. Trans. 81 (2003) 287. [6] B. Jones et al., Phys. Rev. Lett. 104 (2010) 125001. [7] V. L. Kantsyrev et al., Stewardship Science Academic Alliances Annual 2012 report, DOE/NA-0018 (2012) 42. [8] V. L. Kantsyrev et al., Phys. Rev. Lett., subm. (2013). [9] V. L. Kantsyrev et al., Phys. Plasmas, subm. (2013). [10] I. Shrestha et al., High Energy Density Phys. 6 (2010) 113. [11] V.L. Kantsyrev et al., Phys. Plasmas (Letters) 20 (2013) 070702. [12] G.C. Osborne et al, High Energy Density Phys. 9 (2013) 653. [13] V. L. Kantsyrev et al., Phys. Rev. E 84 (2011) 046408. [14] K.M. Williamson et al., Phys. Plasmas 17 (2010) 112705. [15] I. Shrestha et al., IEEE Trans. Plasma Sci. 38 (2010) 658. [16] G.C. Osborne et al., Rev. Sci. Instrum. 83 (2012) 10E103.

55

Measurements of Electron Beam and Subsequent Characteristic Kα and L-shell Emission from Brass Wire-

array Implosions

A.S. Safronova1, V.L. Kantsyrev1, A.A. Esaulov1, I. Shrestha1, V.V. Shlyaptseva1, M.E. Weller1, S.F. Keim1, A. Stafford1

(1)Department of Physics, University of Nevada, Reno, MS 220 Reno, Nevada 89557, United States

Award Numbers: DE-NA0001984, DE-FC52-06NA27586, DE-FC52-06NA27588 DE-FC52-06NA27616, DE-NA0002075

Implosions of brass wire arrays on the 1 MA Zebra pulsed-power generator were used to study electron beams and the subsequent characteristic K-shell and L-shell line emissions. A Faraday cup measured the electron beam. Time-integrated and time-gated spectrometers captured the K- and L-shell radiation.

Electron beam generation in wire array Z-pinches remains elusive. However, their existence is betrayed by the measurements of characteristic K-lines. These characteristic emissions result from the radiative transition of a 2p electron into an n=1 hole. The holes are formed by high-energy electron beams, with energies much larger than the spectroscopically observed thermal electron temperature. Further evidence of electron beams can be confirmed by damage in the form of a cavity in the anode or by Faraday cup measurements.

Though electron beam generation is perplexing, further study is important not only for our fundamental understanding of pinched plasmas, but also because such beams may produce more radiation above 10 keV than from thermal plasmas alone. This mechanism was suggested in [1] as one of the possible concepts for a plasma radiation source in this photon range.

The NTF Zebra pulsed-power generator was utilized for these experiments. It has a peak current of ~1 MA, a ~100 ns rise-time, and an impedance of 1.9 Ω. The large impedance of the Zebra generator allows it to continue to drive current into the stagnated plasma. The loads were comprised

of 24 wires on a 3 mm diameter, compact cylindrical array with a length of 2 cm. The wire material was brass (70% copper, 30% zinc).

The x-ray diagnostic suite includes pinhole cameras, spectrometers, filtered fast x-ray detectors, bolometers, a Faraday cup, and shadowgraphy techniques. This article will focus on results gathered from pinhole cameras, spectrometers, filtered Si-diodes and a Faraday cup.

The diagnostically useful copper and zinc line radiation for brass wire implosions lies between 0.963 and 1.485 keV for the L-shell and between 8.05 and 9.57 keV for the K-shell. The overlapping copper and zinc L-shell spectral lines make the analysis difficult. However, the two radiators are interesting because they can be used to study opacity effects [2,3]. Additionally, doubling the spectral lines can be useful for diagnostics that measure a narrower photon energy range, i.e. a time-gate spectrometer.

In order to interpret the copper and zinc line emissions, a copper and zinc non-LTE kinetic model was used. Energies, radiative and autoionization rates, and cross sections were calculated using the Flexible Atomic Code [4]. Multi-zone radiation transport was accounted for by using the coupling constant formulism [5].

The axial variation in the L-shell ion density and electron temperature was found by comparing a time-integrated L-shell spectrum from Zebra shot #2778 with results from non-LTE kinetic modeling. Electron temperatures ranged from about 360 to 540 eV and ion densities from 1017 to 4×1018

56

cm−3 along the axis of the pinch. Axial positions where the electron temperature was a local minimum tended to have ion densities with a local maximum. Also, the axial positions of local minima of electron temperatures generally passed in-between the hot spot emissions of time-integrated pinhole images of harder radiation (10% transmission of 8.5 keV photons). Thus, the bright spots of the harder photon image are in axial regions of higher temperature and lower ion density L-shell plasma. The fact that this result can be derived from time-integrated data where the L- and K-shell emission lasts ~30 ns suggests that while the stagnating plasma may be changing temporally, it is not doing so spatially.

One is inclined to ask if the bright spot emission from the axially resolved time-integrated spectra correlates with the high ion density or electron temperature. We find for Zebra shot #2778 (for example) that the plasma at z=1.2 cm (measured from the cathode) is at a high density and lower temperature and lies between two bright spots. At z=0.4 cm the plasma is at about the same ion density and electron temperature as it is at z=1.2 cm, but it is also at a bright spot. Position z=0.7 cm is at a region with large gradients in density and temperature. Apruzese et al. [6] found that the bright spots in the copper shot ZR1975 on the Z generator at Sandia National Laboratories were strongly correlated with electron temperatures, while for copper shot Z1616 on the pre-refurbished Z generator there was a correlation with density rather than temperature. Here there are variations of the plasma properties where the L-shell is brightest within the same shot.

Analysis of the time-integrated K-shell spectrum from Zebra shot #2778 shows the presence of chromium and iron Kα from the electron beam interacting with the stainless steel anode and the copper and zinc Kα, Heα, and Kβ lines. The presence of the copper and zinc Heα lines suggests hotter plasmas of keV electron temperatures. K-shell time-gated spectra recorded the zinc Kα, Kβ, and the overlapping copper Kβ and zinc Heα lines. The time history of these

lines shows a correlation between the filtered Si-diode signal (10% transmission at 9 keV) and the Faraday cup signal. The Faraday cup signal was observed to rise during the timings of the K-shell time-gated spectrometer. As the Faraday cup rises, so do the zinc Kα and Kβ lines. However, the overlapping copper Kβ and zinc Heα lines decreases and then increases with time. This could be due to the zinc Heα line dominating over the copper Kβ line at earlier times. It is interesting that the zinc Heα line appears at early times in spite of the long ion-electron equilibration time of ~40 ns. Brass wire array experiments using Zebra with the advanced Load Current Multiplier [7] were recently completed (Oct. 2013). Results from this experiment will provide information about electron beams and Kα emission with an increase in current. Acknowledgments This work was supported by DOE/NNSA Cooperative Agreements DE-NA0001984, DE-FC52-06NA27586, and DE-FC52-06NA27588. It was in collaboration with N.D. Ouart, J.L. Giuliani, A. Dasgupta, J.P. Apruzese (Engility Corp.) and R.W. Clark (Berkeley Research Assoc.) of the Naval Research Laboratory. They are supported by a DOE/NNSA Interagency Agreement with NRL. The authors would like to thank the NTF technical staff for their efforts in conducting experiments on Zebra, supported in part by DE-FC52-06NA27616 and DE-NA0002075.

[1] A. Velikovich et al., IEEE Trans. Plasma Sci. 38, 618 (2010) [2] N.D. Ouart et al., IEEE Trans. Plasma Sci. 38, 631 (2010) [3] N.D. Ouart et al., HEDP 8, 247 (2012) [4] M. Gu, Canadian J. Physics 86, 675 (2008) [5] J. Apruzese et al., JQSRT 34, 447 (1985) [6] J. Apruzese et al., Phys. Plasmas 20, 022707 (2013). [7] A.S. Chuvatin et al., Pulsed Power Conf, IEEE, 975 (2011)

57

Unique Spectral Features from Multi-charged Plasmas Irradiated by Relativistic Sub-picosecond Laser Pulses

on the Leopard Laser at the UNR/NTF

A.S. Safronova1, V.L. Kantsyrev1, A.Y. Faenov1,2, U.I. Safronova1, P. Wiewior1, I. Shrestha1, V.V. Shlyaptseva1, A. Stafford1, M.E. Weller1, Y. Paudel1, O. Chalyy1

(1)Department of Physics, University of Nevada, Reno, MS220, Reno, Nevada 89557, United States

(2)Joint Institute for High Temperatures, Russian Academy of Sciences, Moscow, Russia

Award Number(s): DE-NA0001984, DE-FC52-06NA27586, DE-FC52-06NA27588, DE-FC52-06NA27616, DE-NA0002075

The results of the series of experiments focused on study of x-ray radiation from multicharged plasmas irradiated by relativistic (I > 1019 W/cm2) sub-ps laser pulses on Leopard laser facility at the NTF/UNR are presented. These shots were done under different experimental conditions related to laser pulse and contrast. Using the x-ray diagnostics including a high-precision spectrometer with resolution R~3000 and a survey spectrometer, we have observed several unique spectral features. Specifically, the new L-shell Fe spectral features indicating non-stationary ionization and hot electrons, K-shell Mg features with dielectronic satellites from high-Rydberg states, and the new K-shell F features with dielectronic satellites including exotic transitions from hollow ions are highlighted.

X-ray spectra from plasmas produced by nanosecond lasers have been intensively studied since the 1970s. For example, a typical x-ray K-shell spectra consists of H-like and He-like resonance and intercombination lines and satellites from autoionizing (doubly-excited) states located in the vicinity of resonance lines. Such traditional x-ray laser-produced spectra are similar to those from Z-pinches (as well as from other laboratory plasma sources) and astrophysical plasmas, and are well described by the non-LTE kinetic models when varying the plasma parameters (electron temperature and density, electron distribution function to account for hot electrons, ionization balance, and optical

depth). In the mid-nineties, advances in the development of powerful pico- and sub-picosecond lasers as well as in high-resolution x-ray spectroscopy led to the discovery of the unique spectral features generated in laser-produced plasmas. Generation and observation of such spectral features and the understanding of mechanisms of their production is very important. Despite the substantial progress that has been made since 1995, the needs of systematic experimental x-ray spectroscopic investigations, as well as extended calculations of collisional-radiative ion kinetics in transient non-uniform plasmas with the inclusion of additional to traditional calculations possible processes such as excitation and ionization by hot electrons and photoionization (and other modifications, if needed) are obvious. Recent experiments on the Leopard Laser at UNR have provided an opportunity to study some of these unique features, which will be described below.

The experiments were performed at the Leopard laser facility at NTF/UNR under different experimental conditions related to laser pulse and contrast. In particular, the duration of the laser pulse was 350 fs or 0.8 ns and the contrast was varied from high (10-7) to moderate (10-5). The thin laser targets (from 5 to 750 µm) made of a broad range of materials (from Teflon to iron and molybdenum to tungsten and gold) were utilized. Using the x-ray diagnostics including the high-precision spectrometer with resolution R~3000 and a survey

58

spectrometer, we observed the unique spectral features that are reported in this paper.

The main emphasis of our results in [1] was on specific L-shell spectral features from experiments with Fe and Cu targets and K-shell features from experiments with Mg and Teflon. In particular, the distinct feature of L-shell Fe spectrum produced at the shortest laser pulse of 350 fs and the highest contrast of 10-7 is the manifestation of the large number of ionization stages from non-intense Ne-, F-, and O-like to more intense N-, C-, B-, Be-, and Li-like Fe. The possible explanation of such a large number of ionization stages is the existence of hot electrons that usually influence the spectra by spreading the ionization balance to more ionization stages. A non-LTE iron model, previously applied to model x-ray spectra of Fe from another ultra-short laser plasma experiments [2, 3], describes the spectrum using a small portion (5.8%) of hot electrons. In addition, non-intense spectral features, such as Ne-, F-, and O-like Fe, believed to be produced by the pre-pulse, were fit independently. The most distinct feature of the spectrum produced at the shortest laser pulse of 350 fs but at moderate contrast of 10-5 is the intense spectral lines of Ne-like Fe and Li-like Fe (and less intense neighboring ionization states of F-like and Be-like Fe, respectively). Such a spectrum could not be described by the inclusion of a small portion of hot electrons, but can be explained rather by two plasma electron temperatures (for example, radiation by a pre-plasma stage and by plasma heated by a main pulse) or by non-stationary ionization. The spectrum generated at the longer laser pulse of 0.8 ns and at the same contrast of 10-5 is characterized also by the intense spectral lines of Ne-like Fe as well as F-like Fe, but less intense Li-like Fe spectral features, and resembles the spectrum from Z-pinches.

Summarizing, L-shell Fe spectral features were observed indicating non-stationary ionization and a small portion of hot electrons between 5 and 6% for the sub-ps regime. On the contrary, L-shell Cu

spectra did not express any unusual spectral features except for the sharpening of the line profiles for the data collected at a laser pulse duration of 0.8 ns and an even smaller fraction of hot electrons between 1 and 2 %.

The utilization of the focusing spectrometer with spatial resolution (FSSR) based on the spherically bent mica crystal provides a much better resolution of 3000, which allows us to observe additional spectral features not clearly resolved with the survey spectrometer. For example, the new dielectronic satellite spectral features from K-shell Mg spectra and from K-shell F were observed using the FSSR. In particular, the newly created non-LTE F model based on FAC and dielectronic satellites data calculated with the Cowan code were used to investigate the possible contribution of hollow F ions. The spectroscopic analysis of F spectra has demonstrated the presence of the spectral features from hollow ions as well as their dependence on experimental conditions [4]. Acknowledgments This work was supported by DOE/NNSA Cooperative Agreements DE-NA0001984, DE-FC52-06NA27588, and DE-FC52-06NA27586, and in part by DE-FC52-06NA27616 and DE-NA0002075. It was in collaboration with N.D. Ouart of NRL.

. [1] A.S. Safronova et al, High Energy Density Physics 8, 190 (2012) [2] N.D. Ouart et al, Journal of Physics: Conf. Ser. 244, 042004 (2010) [3] N.D. Ouart et al, Journal of Physics B: At. Mol. Opt. Phys. 44, 065602 (2011). [4] A.S. Safronova et al, “New Spectral Signatures of Hollow Fluorine Ions from Femtosecond Laser-produced Plasmas”, ASOS 2013, Belgium, August 5-9, 2013.

59

Experimental Investigation of Fast-electron Generation Using the Leopard Short-pulse Laser

H. Sawada1, B. Griffin1, T. Yabuuchi2, H. S. McLean3, P. K. Patel3, H. Chen3, J-B. Park3,

and F. N. Beg4

(1)Department of Physics, University of Nevada Reno, MS 220 Reno NV 89557-0220, United States

(2)Graduate school of Engineering, Osaka University, Suita, Japan (3)Lawrence Livermore National Laboratory, Livermore CA, United States

(4)Department of Mechanical and Aerospace engineering, University of California, San Diego, La Jolla CA, United States


Interaction of terawatt short-pulse lasers with a solid target at a peak intensity above ~1018 W/cm2 can generate a significant number of energetic electrons in the relativistic regime. These electrons can play a key role in several applications such as acceleration of energetic protons and ions through a target normal sheath acceleration (TNSA) mechanism [1], bright monochromatic x-ray source generation [2], isochoric heating of a solid target [3], and core heating for electron Fast Ignition laser fusion [4]. Detailed electron characterization is important both for those applications and for understanding the fundamental physics of fast electron generation and transport.

Generation of fast electrons depends on the laser peak intensity, as well as other laser parameters prior to the main pulse, such as pedestal intensity, duration and optimized focal spot size (usually with an off-axis parabolic mirror). The preplasma, created by the pedestal, changes the interaction condition and leads to a reduction of conversion efficiency from the laser to the electrons. Thus, it is important to measure laser pedestal energy and the intensity trace on each shot.

We have conducted a 50 TW Leopard laser experiment to characterize fast electrons by measuring energy partitioning from the laser to the electrons, protons and K-alpha x-rays while the development of a pre-pulse monitor is underway. Fig. 1 shows the laser and diagnostic layout inside the Phoenix chamber. The Leopard laser system

at the Nevada Terawatt Facility (NTF) delivered 15 J of energy in a 0.35 ps pulse. Limiting the beam spot size to within ~8 µm allowed for the target interaction to reach a peak intensity of 1019 W/cm2 at 20° incidence angle. The nominal laser intensity contrast was 108 [5]. The size of the Cu foil targets varied from 2 µm to 20 µm in thickness and from ~ 50 µm by 50 µm to 2000 µm by 2000 µm in surface area. A Bragg crystal x-ray spectrometer and a spherical crystal imager were used to measure x-rays in the range of 7.5 - 9.5 keV as well as a 8.05 keV 2-D monochromatic x-ray image. The escaping electrons and protons in the target rear were monitored with a magnet-based electron spectrometer and radiochromic film. Simultaneous measurements of the x-ray and charged

Fig. 1 Leopard Laser and Diagnostic Set-up in the NTF Phoenix Experimental Chamber.

60

particles with absolutely calibrated diagnostics allow us to infer the energy partition.

Fig. 2 shows the monochromatic x-ray images of the 300 µm by 400 µm and 60 µm by 75 µm Cu foils. The electrons generated are confined within the Cu foil and induce the K-alpha emission. The bright spot represents the laser-foil interaction with respect to the foil. The x-ray spot size is nominally larger than the laser spot because

of the electron refluxing near the interaction point. K-alpha emission from the entire foil was observed from a foil with a surface area of less than 1 mm by 1mm.

Fig. 3 shows the measured escaping electrons. The slope temperature of ~ 1.5 MeV was inferred both from large and small targets. The number of electrons from the large target was significantly higher than the number from the small target.

The x-ray spectra recorded with the flat crystal spectrometer are shown in Fig. 4. Primarily, Cu Kα and Kβ x-rays originated from the solid part of the target and the Cu Heα emission is from a low-density, ablated region. The difference in the K-line x-rays is attributed to target size. The same Heα emission from two different targets indicates a similar preplasma generation. A detailed spectral analysis could possibly be used to estimate the spatial scale of the preplasma. The bulk temperature of the foil will be inferred from the ratio of Kβ/Kα lines.

The radiochromic film has been scanned with an absolutely calibrated scanner. Preliminary analysis shows a maximum proton energy of ~ 5 MeV. An estimate of the proton energy spectrum and proton flux in absolute units is underway.

The authors would like to acknowledge O. Chalyy and P. Wiewior for the laser operation and V. Nalajala, A. Astanovitskiy and V. Davis for supporting the laser shots as shot directors. T. Y. was supported by Japan/U.S. Cooperation in Fusion Research and Development. [1] S. C. Wilks et al., Phys. Plasmas 8, 542 (2001) [2] H.-S. Park et al., Phys. Plasmas 13, 056309 (2006). [3] P. M. Nilson et al., Phys. Rev. E 79,

016406 (2009) [4] R. Kodama et al., Nature 412, 798–802 (2001) [5] P. Wiewior (private communication,

2013

Fig. 2 Monochromatic X-ray Images from (left) 300 by 400 m and (right) 60 by 75 m Cu Foils in Same-color and Spatial Scale.

Fig. 3 Measured Escaping Electron Spectra from Large (1000 by 1000 m) and Small (60 by 75 m) Cu Foils.

Fig. 4 Measured Normalized X-ray Spectra from the Large and Small Cu Foils.

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Results of Experiments with Mixed Nested Wire Arrays and Silver Planar Wire Arrays on Zebra with an Application to

Lasing

M.E. Weller1, A.S. Safronova1, V.L. Kantsyrev1, A.A. Esaulov1, I. Shrestha1, V.V. Shlyaptseva1, A. Stafford1, G.C. Osborne1, S. F. Keim1, E.E. Petkov1

(1)Department of Physics, University of Nevada, Reno, MS 220 Reno, Nevada 89557, United States

Award Number(s): DE-NA0001984, DE-FC52-06NA27588, DE-FC52-06NA27586, DE–FC52-06NA27616, DE-NA0002075

The results of two different directions of the most recent research are highlighted. They are experimental and theoretical studies of implosion and radiative characteristics of mixed nested cylindrical wire arrays and of radiation from silver Z-pinch plasmas with application to lasing.

The first research direction was combined experimental and theoretical studies of mixed Nested Cylindrical Wire Arrays (NCWAs) on the NTF Zebra pulsed-power generator [1]. NCWAs have been studied extensively at Sandia National Laboratories on the 20 MA, 100 ns rise time Z-machine and have demonstrated an increase in X-ray power and reduction of pulse width [2] as compared to single wire arrays, producing pulse shapes required for inertial confinement fusion [3]. An important issue for NCWAs is an understanding of how the inner and outer arrays radiate and implode. It was shown in Ref. [4], using mixed Al (5056) and SS (304, 69% Fe, 19% Cr, 9% Ni) NCWAs on the 1 MA, 100 ns rise time COBRA generator at Cornell University, that the outer wire array radiates more intensely than the inner wire array. This was explained as the outer array having more kinetic energy than the inner array (due to its larger radius), though the complexity of nested arrays due to current switching and varying levels of inner penetration of the outer array to the inner array makes this conclusion difficult to estimate. In this paper, we present an extension of the work in Ref. [4] by comparing K-shell Al and other L-shell mid-Z elements, specifically mixed brass (70%

Cu, 30% Zn) and Al (5056) NCWAs on the 1 MA, 100 ns rise time Zebra generator at UNR.

The second direction of research focused on radiation from silver wire array Z-pinch plasmas on Zebra with an application to lasing [5, 6]. Planar wire array (PWA) configurations in Z-pinch experiments have been shown to be very efficient radiators [7]. As part of this research, different wire materials have been tested in a search for more efficient radiation sources. In particular, silver (Ag) wire arrays were recently introduced as efficient x-ray radiators and have been shown to create L-shell plasmas that have the highest electron temperature (>1.8 keV) observed on the Zebra generator so far, and upwards of 30 kJ of energy output, which is of interest for inertial confinement fusion, as well as for other applications [8]. It was also shown that Ag radiated from many “bright” spots along the pinch, with “cold” Lα and Lβ lines observed in more “column-like” features along the pinch between the bright spot formations. One of the important questions to be answered in this research is how these L-shell Ag plasmas evolve over time. To help answer this question, a time-gated x-ray spectrometer was developed and fielded which was designed to capture L-shell Ag lines. Many of the early Ag experiments were performed on the Zebra generator in what is now referred to as the “standard” 1.0 MA configuration with a 100 ns rise time. The new Load Current Multiplier (LCM) allows for experiments to be performed at currents as high as 1.7 MA, which allows for

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many useful comparisons. Experiments in this research program included both standard and enhanced LCM results.

The dynamics of mixed nested cylindrical wire arrays were also studied at the UNR Zebra generator with our existing theoretical and experimental tools to better understand the contributions of each array to the emitted radiation. In particular, experimental results of mixed brass (70% Cu, 30% Zn) and Al (5056, 5% Mg) nested cylindrical wire arrays are analyzed and compared. The loads consisted of brass in the inner array and Al in the outer array, or alternately, Al in the inner array and brass in the outer array, with a mass ratio of 1:1 (outer to inner). Consequently, radiative properties of K-shell Al and Mg ions and L-shell Cu and Zn ions were compared as functions of the placements of the brass and Al wires on the inner and outer arrays. Results show that the placement of brass and Al, whether on the inner or outer array, dramatically affects the intensity of the x-ray emission. Specifically, the ratio of Cu L-shell to Al K-shell emissions changed from 4, when Al is placed in the outer array, to 40, when brass is placed in the outer array, and the total radiated yield was highest when the brass was on the outer array (18 kJ, versus 15 kJ when brass is on the inner array). Each load was fielded twice to vary the timing of the time-gated imaging and spectral diagnostics. This technique provided a more complete understanding of the evolution of the plasma parameters over the x-ray pulse, and thus highlights the importance of the time-gated diagnostics.

Results of experiments consisting of various single planar wire arrays (SPWAs) and double planar wire arrays (DPWAs) of Ag and mixed Ag and Al that were tested on the UNR Zebra generator are here presented and compared. To further understand how the L-shell Ag plasma evolves over time, a time-gated x-ray spectrometer was designed and fielded, which has a spectral range of approximately 3.5 – 5.0 Å. With this spectrometer, L-shell Ag, as well as cold Lα and Lβ Ag lines, were captured and analyzed along with PCD signals (> 0.8

keV). In addition, other signals, from such diagnostics as filtered XRD (> 0.2 keV) and Si-diode (SiD) (> 9 keV) detectors, covering a broad range of energies from a few eV to greater than 53 keV, were captured and analyzed. The observation and analysis of cold Lα and Lβ lines show possible correlations with electron beams and SiD signals. Recently, an interesting issue regarding these Ag plasmas is whether lasing occurs in the Ne-like soft x-ray range, and if so, at what gains? To help answer this question, a non-LTE kinetic model was utilized to calculate theoretical lasing gains. It is shown that the Ag L-shell plasma conditions produced on the Zebra generator at 1.7 MA may be adequate to produce gains as high as 6 cm-1 for various 3p → 3s transitions. Other potential lasing transitions, including higher Rydberg states, are also included in detail. The overall importance of Ag wire arrays and plasmas is discussed.

Acknowledgments This work was supported by DOE/NNSA Cooperative Agreements DE-NA0001984, DE-FC52-06NA27588, and DE-FC52-06NA27586. It was in collaboration with J.P. Apruzese (Engility Corp.) and J.L. Giuliani, of the Naval Research Laboratory, C.A. Coverdale of Sandia National Laboratories, and A.S. Chuvatin of Ecole Polytechnique. The authors would also like to thank the NTF technical staff for their efforts in conducting experiments on Zebra supported in part by DE-FC52-06NA27616 and DE-NA0002075. [1] M.E. Weller et al, HEDP 8, 184 (2012) [2] C. Deeney et al, PRL 81, 4883 (1998) [3] M.E.Cuneo et al, PRL 95, 185001 (2005) [4] A.S. Safronova et al, Phys. Plasmas 15, 033302 (2008) [5] M.E. Weller, RHEDP 2013, Invited talk [6] M.E. Weller, SSAP Annual, DOE/NA-0019, 29 (2013) [7] V.L. Kantsyrev et al, HEDP 5, 115 (2009). [8] A.S. Safronova et al., HEDP 7, 252 (2011).

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Plasma Formation and Evolution from a Copper Surface Driven by a Mega-ampere Current Pulse

K.C. Yates1, B.S. Bauer1, S. Fuelling1, T.J. Awe2, V.V. Ivanov1, S.D. Altemara1,

D. Papp1, A.A. Anderson1, G.A. Wurden3, R.E. Seimon1, I.R. Lindemuth1, R.S. Bauer4

(1) Nevada Terawatt Facility, Department of Physics, University of Nevada, Reno, MS 220 Reno, Nevada 89557-0058, United States

(2)Sandia National Laboratory, Albuquerque, NM, United States (3)Los Alamos National Laboratory, Los Alamos, NM, United States

(4)Davidson Academy of Nevada, Reno, NV, United States

Award Number(s): DE-FG02-04ER54752, DE-FC52-06NA27616, DE-NA0002075

The interaction of an intense current with a conductor, leading to changes of state, is exceptionally important for both basic physics and applications such as MagLIF. This process raises many interesting questions, such as the influence of the electrothermal instability on plasma initiation and evolution. A novel barbell-shaped load has enabled experiments that isolate the effect of high current density, without interference from plasma formed by high electric fields.1 This low-inductance load has a central mm-diameter rod (the region of study), but 6-mm-diameter ends. The geometry eliminates the direct lines of sight from plasma at electrical contacts to the surface under investigation. Recently, copper 101 rods of diameter 0.7 mm, 0.8 mm, 1.0 mm, and 1.59 mm were driven by the 1-MA Zebra current pulse. The current is consistent, independent of the initial rod diameter (to within a few percent) within a given experimental campaign. The heated surface of liquid, vapor, and/or plasma is investigated with a wide variety of optical, ultraviolet, and laser diagnostics. The data collected from these experiments on copper are being directly compared with results on aluminum 6061.2,3

A multi-element photodiode array surface temperature diagnostic measured the surface temperature as a function of time. The load is imaged (at magnification 5.6) through a green band-pass filter and an IR filter to a single-substrate linear array of 38 optical diodes. This yields the time evolution of surface brightness temperature

at various axial locations along the load. The magnification is sufficient to have the image of the rod span the full width of the diode elements, so that the diameter of the emitting load does not affect the diode signal. The photodiode array confirms the axial uniformity of emissions from barbell loads with knife-edge contacts. Assuming blackbody radiation, a surface temperature was determined. The Cu peak temperature was ~3eV for 0.8-mm-diameter loads and ~8eV for 0.7-mm-diameter loads. For 1.0-mm-diameter and 1.59-mm-diameter loads, the Cu surface temperature was lower than 0.6 eV and 0.4 eV, respectively, and plasma was not observed.

High-resolution, 2-ns-time-gated imaging was used to examine the surface of copper during plasma formation. These images show remarkable similarity to previous images of aluminum surfaces (Fig. 1), despite the great difference between the Cu and Al oxide surface layers. For those loads which form plasma, optical emission from the plasma surface is initially non-uniform, showing discrete bright spots. Next, plasma filaments form, both along the current and transverse to it. The emission ultimately becomes quite uniform as the surface temperature increases. The linear photodiode array also observes increasing emission uniformity with increasing time and temperature. The uniformity of the fully formed plasma supports comparing the data with the results of one-dimensional modeling.4

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A: Copper 650 kA

C: Aluminum 592 kA

B: Copper 850 kA

D: Aluminum 745 kA

Fig 1. Time-gated imaging shows similarity in evolution of copper and aluminum surfaces.

An additional diagnostic of the surface temperature is provided by time-resolved EUV spectroscopy and by filtered EUV photodiode measurements. In past experiments with aluminum 6061 loads, the EUV spectrometer recorded wavelengths from 8 to 18 nm. In recent experiments, the Al-6061 spectral measurements have been extended to wavelengths from 8 to 56 nm. For the copper loads, the spectral range was 35-70 nm. No distinct copper lines were observed by the spectrometer, only a continuum. The EUV photodiodes showed strong signals starting at the time of plasma formation.

The expansion of rod material is a critical parameter for a variety of applications. The radius of the copper is measured at various moments with a short pulse of green as well as UV laser light, using shadowgrams. The shadowgrams show an opaque object with a well defined surface that expands uniformly in radius until near peak current. There is an interesting comparison to be made between the 0.7- and 1.00-mm-diameter copper loads. The 0.7- and 1.00-mm-diameter loads expand at a similar rate of 3.3 km/sec and 3.5 km/sec respectively despite the fact that the 0.7-mm load forms plasma and the 1.00-mm load does not. As the current profile approaches peak value, the dI/dt changes sign as the magnetic flux leaves the system. As the field lines expand outward, the plasma is no longer pinned up against

the load and begins to expand outward at a higher expansion velocity of 10 km/sec. The loads that do not form plasma do not display this phenomenon, and continue to expand at constant velocity through peak current. This phenomenon was also observed previously with aluminum 6061.

With the diagnostics discussed above, we were able to determine the time of plasma formation (determined by a sharp rise in temperature by the visible photodiode array (Fig. 2)) and the surface magnetic field at the time of plasma formation. There appears to be a threshold for plasma formation of ~3.3 MG that does not depend on load diameter. This is compared to a threshold that was observed for aluminum to be ~2.2 MG. Only two different diameters of copper formed plasma, and for the larger one (0.8-mm-diameter), the time of plasma formation was so late as to be in the start of the nonlinear part of the current profile. With this in mind, it would be of great interest to field copper loads of smaller diameter, such as 0.5-mm and 0.6-mm, to more firmly establish that the threshold for copper is 3.3 MG.

TBB(t) for MG-VI Copper Loads

00.20.40.60.8

11.21.41.61.8

2

75 95 115 135 155 175 195

time[ns]

TBB

[eV]

Shot 2869 (0.67mm)

Shot 2871 (0.70mm)

Shot 2874 (0.69mm)

Shot 2877 (0.69mm)

Shot 2858 (0.80mm)

Shot 2864 (0.80mm)

Shot 2868 (0.86mm)

Shot 2873 (0.84mm)

Shot 2876 (0.83mm)

Fig. 2. The abrupt increase in temperature is interpreted as the time of plasma formation. [1] T.J. Awe, B.S. Bauer, S. Fuelling, and R.E. Siemon, Phys. Plasmas 18, 056304 (2011). [2] T.J. Awe, B.S. Bauer, S. Fuelling, and R.E. Siemon, Phys. Rev. Lett. 104, 035001 (2010). [3] T.J. Awe, B.S. Bauer, S. Fuelling, and R.E. Siemon, IEEE Trans. Plasma Sci. 39, 2418 (2011). [4] I.R. Lindemuth, R.E. Siemon, B.S. Bauer, M.A. Angelova, and W.L. Atchison, Phys. Rev. Lett. 105, 195004 (2010).

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Operations / Facilities

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Mechanical Engineering and Support of Experiments at the NTF

A. Astanovitskiy1, O. Dmitriev1, D. Shedd1, P. Borda1

(1)Nevada Terawatt Facility, Department of Physics, University of Nevada, Reno, MS 220 Reno, Nevada 89557-0058, United States

Award Number(s): DE-FC52-06NA27616, DE-NA0002075 The NTF Mechanical Engineering and Development (ME&D) group performs many key tasks to support the NTF’s scientific program. Their main responsibilities include mechanical design, fabrication, and operation of experiments in the NTF’s pulsed-power and laser facilities. The ME&D team supports researchers in the planning and execution of new experiments. The ME&D group’s responsibilities for the Zebra pulsed-power generator include load-chamber operation and maintenance of the pulse-forming section and vacuum systems. In addition, the ME&D team also provides support for actual shot operations by providing personnel for experiments on the Z-pinch generator who act as safety and console operators, and shot directors.

Fig. 1 NTF Wire-array Load Designs. The ME&D group is deeply integrated into the experimental campaign preparation process. To support the design part of this task, the group consists of a mechanical

engineer and a development technician II. Mechanical engineering students also provide support, thus gaining valuable experience. Finally, the design of Zebra wire load hardware is a one of the group’s major tasks (Fig. 1).

Fig. 2 X-ray Spectrometer Pro-E Model.

The ME&D group also supports the design and fabrication of various diagnostics, (Fig.2), as well as the full manufacturing cycle. For this the group relies on two machine shops. One located at NTF; the other at the UNR D/PHYS. All members of the group are trained to safely operate complicated shop equipment. For mass-produced parts, the shop is equipped with a CNC mill and lathe. In special circumstances, the NTF collaborates with outside machine shops. These companies produce over-size parts or use Wire Electrical Discharge cutting Machines (EDM). The EDM process is frequently utilized in the NTF load-fabrication process. Recent major Zebra upgrades overseen by the ME&D team include

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upgrades to the Zebra oil and water tanks, mechanical design and fabrication of the load current multiplier (LCM), and the coupling of the Leopard laser beam into the Zebra’s load chamber. The LCM (Fig.4) improves the performance of Zebra and has already increased the load current from 0.9- to 1.7-MA.

Fig. 4 LCM in the Zebra’s Load Chamber.

The vertical Leopard laser beam access was implemented to support coupled Zebra-Leopard experiments. It allows for the focusing of the Leopard beam with an Off-Axis Parabola (OAP) in the short pulse mode (~350 fs) (Fig. 5). The aluminum six-inch OAP was recently used to create laser-produced protons for plasma radiography experiments in the Zebra.

Fig. 5 OAP Focusing System in Zebra.

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NTF Operations and Maintenance

D.T. Macaulay, G. Ferguson, and V. T. Davis



The NTF Operations and Maintenance (O&M) group provides essential services to support the research effort. Broadly speaking, services include research tool and laboratory O&M, electrical and mechanical design/installation, custom fabrication, planning, management and execution of building alterations, safety program development and administration, property management, and regular interface with constituents internal and external to UNR.

Research tool and laboratory O&M includes collaboration with internal engineering resources to routinely operate and maintain the Zebra Z-pinch machine and its subsystems, support for diagnostics development, facilities support for laser systems and infrastructure, development and operation of machine and fabrication shops, safety implementation and enforcement, and consumable supply management.

More specifically, O&M services include continuous monitoring to ensure safe operation, certified Zebra console operation and shot direction, crane operation and confined-space entry for energy storage and pulse-forming section repair and maintenance, rebuild/repair of principal pulsed-power components and systems, regular maintenance of dielectric fluids, and assurance that personal protective equipment, solvents and gases are continuously available. General laboratory housekeeping is also provided, to include the recent conclusion of an 18-month project to dispose of tons of scrap materials that had been accumulating for over a decade.

Design, installation, and custom fabrication services include electrical power distribution, dedicated chilled water service, cleanrooms and clean work stations, safety warning and interlock systems, custom safety system hardware, Faraday cages,

instrument mounts, and fluid handling systems. Specifically, electrical distribution enhancements include panel, receptacle and hard-wire installations for all major labs and experiment systems, plus the cluster computer and machine shop.

Chilled water service includes a10-ton precision liquid-to-air chiller located outdoors, dedicated to laboratory equipment. The insulated copper piping is configured as an extendable recirculating loop with multiple points of connection, serving the Leopard laser, turbo pumps on the Phoenix target chamber, Falcon compressor and Leopard beam transport, a cryo compressor, the Cheetah laser, and the Cheetah cleanroom. The next planned extension of the loop will serve the Coherent laser located in the Spectroscopy lab, and evaporators located in the Materials Science lab. Completion of the loop will serve the EKSPLA and Tomcat lasers, presently served by a portable chiller.

The final feature presently planned is redundancy, by parallel installation of an auxiliary chiller unit. Cleanrooms include the Cheetah laser and Falcon compressor cleanrooms. The Cheetah laser cleanroom is a manufactured steel frame/vinyl curtain enclosure that includes HEPA (high-efficiency particulate air) filters, modular ceiling panels, and recessed fluorescent lighting. It was specified according to the laser manufacturer’s minimum requirement of Class 50,000, although actual performance far exceeds the minimum requirement. Temperature controls were provided in-house. The Falcon compressor cleanroom employs the same enclosure style, but has no internal temperature controls and was essentially fabricated in-house. Clean work stations (areas where clean air is delivered to partial enclosures)

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serve the Leopard laser front-end, and maintenance/assembly for microchannel plate components that are part of core diagnostics systems. Safety warning and interlock systems include raceways, enclosures, contact switches and wiring for magnetic door locks, illuminated signs and beacons, door interlocks for laser shutters and high-voltage switchgear, and a main power disconnect (emergency stop) for the cluster computer room. Custom hardware includes laser wall shutters, door switch enclosures, beam enclosures, and Faraday cage components. Recently, a new generation of laser wall shutters and shutter enabling controls was installed. Fluid handling systems cover 50/50 water/propylene glycol for chiller service, dielectrics (8000 gal. mineral oil and 15,000 gal. deionized water in Zebra), SF6 (for high-voltage switchgear), and N2 (for cleaning utility, chamber backfill, and laser disc amplifier cooling).

Building alteration services from inception include the conceptual bases for major reconfiguration to accept the Zebra z-pinch, management and substantial physical contribution to the building alterations and the installation of the z-pinch, development of accommodations for the Leopard and Cheetah lasers and cluster computer, and most recently, a full electrical upgrade to the Cheetah laser bay and Materials Science laboratories. Recent and important features common to the main first-floor labs (Zebra, Leopard, Cheetah, Spectroscopy, Pulsed-Power, and Materials Science) are the updated and customized HVAC and electrical distribution systems. Together these systems provide environmental controls properly suited to the research needs, with built-in flexibility and expandability. Although these installations per se were executed by outside contractors, essential development, field engineering and management services were provided directly by the NTF Facilities and Operations group.

Safety program development and implementation are continuing processes, particularly since commissioning of the NTF Operational Readiness Assessment in 2004.

Staff members at all levels seek to identify new hazards as existing conditions change, to carefully analyze new experiment configurations to mitigate hazards, and to inform all personnel appropriately. Recently, engineering safety control systems underwent a major renovation and update to bring the NTF into closer compliance with national safety norms; administrative controls have been revisited and enhanced on numerous occasions, and continue to be, when justified by newly-identified hazards or deficiencies. With help from the UNR administration, NTF has redefined its collaboration with the UNR Department of Environmental Health and Safety (EH&S), to develop and ensure a more comprehensive, consistent, and highly integrated approach to safety as we move into the future.

A comprehensive property inventory procedure overhaul took place in 2011 at the NTF. This process involved combining all previous inventory lists into a single database, together with a physical inventory of the premises. The information was sorted and cross-checked, leading to a valid control of current inventory for the first time. The database and verification processes were refined and systematized, with the goal of making periodic inventories quick, painless, efficient, and accurate.

The Facilities and Operations group maintains active relations with several departments and organizations that are relevant to the NTF and the physical plant that it occupies. In addition to UNR EH&S, ongoing collaborations with the several divisions of UNR Facilities Services, Police Services, academic departments and other UNR administrative departments helps keep relevant parties informed and processes moving smoothly. Open communication with the Office of the State Fire Marshal, Nevada State Public Works, Reno Fire Department, City of Reno Environmental Control, and the Washoe County Air Quality office help keep those agencies informed, and comfortable with NTF citizenship.

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Electrical Engineering and Experimental Support on the 1 MA Zebra Z-pinch Machine and the 50 TW Leopard Laser System

V. Nalajala1, Z. Johnson1*, R. Obenauf1, L. Hennessey1

(1) Nevada Terawatt Facility, Department of Physics, University of Nevada, Reno, MS 220

Reno, Nevada 89557-0058, United States Award Number(s): DE-FC52-06NA27616, DE-NA0002075

The Electrical Engineering Section at the Nevada Terawatt Facility (NTF) consists of an Electrical Engineer and two undergraduate students. The mission of the group is to provide working diagnostics, safety systems and data support; to aid in scientific operations and maintenance; to train and guide students; and to provide any and all electrical engineering support that is required by researchers (and the rest of the facility).

The EE group develops, supports, and maintains pulsed-power systems, safety systems, data acquisition and control systems, and core experimental diagnostics. The group also performs data analysis and timing setup. Students are actively involved in development, experiments support and operations, and contribute significantly to the achievement of NTF goals.

The number of Z-pinch, laser and coupled shots performed each month at the facility over the last three years is shown in Fig. 1 (2011), Fig. 2 (2012) and Fig. 3 (2013).

Fig 1. Breakdown of shots (by type) at the NTF in 2011.

Fig. 2. Breakdown of shots (by type) at the NTF in 2012.

Fig. 3. Breakdown of shots (by type) at the NTF in 2013.

In August 2011, the Leopard laser command system, which operates the laser remotely through a LabVIEW-based program, was upgraded to control and operate the pulsed-power system for the second 94mm amplifier and faraday rotator in addition to the existing 6mm, 2x19mm, 45mm and original 94mm amplifiers. Fig. 4 shows the updated front panel of the Leopard command program.

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Fig. 4. The Leopard Command Program. In November 2011, the data acquisition system was upgraded to make it more reliable and easier for staff and researchers to acquire and process shot data efficiently. Fig. 5 shows the front panel of the DAQ program developed in LabVIEW 2010.

Fig. 5: Data Acquisition Program. The NTF considers the safety of its personnel as a top priority. And in a continuing effort to improve safety and to be in compliance with ASCI standards, during the period June 2012-July 2013, the safety systems have been re-designed, re-engineered, and upgraded throughout the facility in a coordinated effort that included the Mechanical Engineering Team and the Facility Staff. In addition, all the laser room safety indicators have been modified. The flashing beacons outside the doors have been replaced with two-way illuminated door signs. Inside the labs, blinking LED lights have been set up to indicate the hazards existing on the other side of the doors.

A new laser shutters control system has been designed and developed in the

Zebra lab (SAGE Room 107) that operates all diagnostic laser shutters from a single control panel. Illuminated signs have been placed in strategic locations throughout the bay to indicate each laser shutter status inside the lab.

The Zebra lab safety system has been redesigned and upgraded to reflect ASCI standards, to indicate the appropriate hazards on all active entrances to the Zebra lab, and to provide a more reliable control system. The flashing beacons outside the doors have been replaced with illuminated door signs that indicate the hazards and the status of energized HV or laser systems inside the lab (SAGE Room 107). The status of the laser shutters is also monitored by the safety system. Fig. 6 shows an image of the front panel control of the safety system developed in LabVIEW 2010.

Fig. 6. The Zebra Lab Safety System Control Interface Panel. In the future, we hope to provide a user interface for researchers to perform shot data and statistical analysis in real time, to automate the Zebra console for more reliable performance, and to continue to support NTF experiments and the NTF mission for many years to come. We would like to acknowledge the efforts of the Mechanical Engineering team and other NTF staff members for their support.

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Leopard II Laser Development

P. Wiewiór and O. Chalyy




In the years covered by this report, The NTF’s Leopard laser has been heavily utilized. Nevertheless, a number of improvements have been made to the laser. This article briefly describes these improvements and their impact on its performance. A brief description of the Leopard laser is presented as well.

The 50-TW Leopard II laser is the workhorse of the high-intensity laser-matter interaction program at the NTF. The Leopard II is an ultra-intense, ultra-short hybrid Ti:Sapphire/Nd:glass system, that can be operated in long-pulse (90 J, 0.8 ns) or short-pulse (15 J, 0.35 ps) modes, and is available for stand-alone or coupled experiments with the Zebra puled-power generator. The system contains several major subsystems: a femtosecond front-end (oscillator, stretcher, and regenerative amplifier), rod and disk flashlamp-pumped amplifier sections, grating compressor, beam transport lines, adaptive optics, diagnostics, and a control system. The detailed technical description of the Leopard laser can be found elsewhere [1]. With a lot of hard work by the Leopard staff, the Leopard laser operates on a daily basis and many successful experimental campaigns were conducted. A 1000th experimental shot from Leopard laser was fired in May 30, 2013 during a Leopard-Zebra coupled campaign.

The configuration of the amplifier chain in the Leopard laser is such that pulses from the oscillator are amplified first in the Ti:Sapphire regenerative amplifier operating at 500 Hz, and then in a number of Nd:glass flashlamp-pumped amplifiers operating in a single-shot mode. A Pockels cell located aft of the stretcher and between crossed polarizers rejects all except the desired pulses at a 500-Hz frequency. A second fast Pockels cell aft of the regenerative amplifier

limits the pulse frequency to 100 Hz. A third Pockels cell is located after the first Nd:glass amplifier. As a consequence of the leakage of the three Pockels cells, a small pre-pulse arrives at the target before the main pulse. This is relatively unimportant for gas-target experiments, but when solid targets are used it can be a serious problem. With the three Pockels cells as described, the best obtainable contrast ratio was around 106:1, resulting in a pre-pulse intensity on target of more than 1012 W/cm2, leading to pre-plasma formation on solid targets. In preparation for proton-production experiments using thin foil targets, it was decided to add an additional large-diameter Pockels cell before the 45-mm diameter Nd:glass rod amplifier to improve the contrast. A new pre-pulse monitor was also constructed so the effect of the additional Pockels cell could be measured. With the new Pockels cell installed, the typical contrast ratio is now 108:1 or better at the nanosecond time scale.

During the first years of operation of the Leopard laser, a demand for higher pulse energy in the long-pulse mode was expressed by many experimenters. To address these requests, it was decided to prepare and install a second 94-mm diameter Nd:glass disk amplifier along with a pulsed Faraday isolator (with the same diameter) for rejecting back-reflections. A special service station for disk amplifiers was built and the second amplifier was assembled, tested, and installed in the Leopard amplifier chain. The first 94-mm disk amplifier was serviced as well, including a cleaning, and realignment, and the replacement of one of Nd:glass disks. The laser after this upgrade is called Leopard II and is capable of delivering up to 90 J in the long pulse mode of operation (0.8 ns).

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The next amplifier to be upgraded is the smallest one: the 6-mm diameter Nd:glass rod amplifier. This amplifier is approx. 40 years old. Despite many improvements and repairs over the years, this amplifier has always presented a reliability issue and is a source of constant problems. A new 9-mm diameter amplifier was ordered from Quantel, and was delivered in 2013, and will be installed shortly. A schematic of the new Leopard II is shown in fig. 1.

Fig.1. The Leopard II Laser. The 6mm amplifier will be replaced by a new 9mm amplifier in the near future.

During the years that the Leopard has

been in operation, various experiments have required pulses of different lengths: short (compressed) and long (uncompressed). These have generally been obtained by realigning the beam path inside the compressor by the Leopard staff. Aligning the beam path and compressor was a lengthy and complicated process. A new technique was developed to change the pulse duration mode in a reasonably short period of time. New additions included a sliding roof mirror, which retro-reflects the incident beam before the first grating, and a beam position monitor. A new alignment procedure was also developed. The diffraction gratings inside the Leopard compressor are gold-coated with a relatively low laser damage threshold. We faced a catastrophic damage to one of these sets two years ago. The whole compressor chamber was subsequently refurbished, and a new set of gold gratings was installed and aligned.

For optimal performance, the Leopard laser is equipped with an adaptive optics (AO) system, which is tailored to the Leopard’s beam parameters. A crucial part of the AO system is the deformable mirror, which is used as a wave front corrector. The original mono-morph mirror was coated with a protective aluminum layer and after a couple of years of operation, the protective coating showed signs of serious damage. We replaced the old mirror by the new generation, dielectrically-coated, ILAO deformable mirror (Imagine Optic). The new mirror has many advantages, including a much higher damage threshold, increased temporal stability, and improved reliability.

The most important application of the Leopard laser at the NTF is in experiments in which the Zebra Z-pinch generator and the Leopard laser are coupled together. An example is the (Leopard-generated) proton deflectometry of Z-pinch plasmas successfully developed by NTF and UCSD teams. For such coupled experiments, a triggering accuracy and low temporal jitter between Leopard (and Zebra) is crucial. The Zebra generator is not (yet) equipped with a laser-triggered switch, so it has a temporal jitter of approx. 20 ns. Consequently, the Leopard acts as a master clock during coupled experiments, and so the Leopard timing jitter has to be as small as possible. During the first of these types of experimental campaigns, we discovered the Leopard jitter to be surprisingly high and unpredictable. After extensive troubleshooting, we identified the source of this erratic behavior: the 80 MHz signal from the fs oscillator was prone to EMI from discharging flashlamps, causing interruptions in the 80 MHz clock signal. An external photodiode installed in a Faraday cage and additional monitoring of the 80 MHz signal from the oscillator via optical fiber solved the problem, and the temporal jitter from the Leopard laser is now below 1 ns, as expected. [1] P. Wiewior et al., J. Physics: Conference Series, 244, 032013 (2010).

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Publications & Presentations

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YEAR 2013 2013 Publications (10) 1. S. Chawla, M. Wei, R. Mishra, K. Akli, C. Chen, H. McLean, A. Morace, P. Patel, H.

Sawada, Y. Sentoku, R. Stephens, and F. Beg, “Effect of Target Material on Fast-Electron Transport and Resistive Collimation”, Phys. Rev. Lett. 110, 025001 (2013).

2. H. Chen, M. Nakai, Y. Sentoku, Y. Arikawa, H. Azechi, S. Fujioka, C. Keane, S. Kojima, W. Goldstein, B. R. Maddox, N. Miyanaga, T. Morita, T. Nagai, H. Nishimura, T. Ozaki, J. Park, Y. Sakawa, H. Takabe, G. Williams, and Z. Zhang, “New insights into the laser produced electron–positron pair,”, New J. Phys. 5, 065010 (2013).

3. V. V. Ivanov, A. A. Anderson, D. Papp, A. L. Astanovitskiy, B. R. Talbot, J. P. Chittenden and N. Niasse, “Current redistribution and generation of kinetic energy in the stagnated Z pinch”, Phys. Rev. E 88, 013108 (2013).

4. V.V. Ivanov, D. Papp, A.A. Anderson, B. Talbot, A.L. Astanovitskiy, V. Nalajala, O.

Dmitriev, J.P. Chittenden, N. Niasse, S. Pikuz, and T. Shelkovenko, “Study of Micro-pinches in Wire-array Z Pinches”, Phys. Plasmas 20, 112703 (2013).

5. V.L. Kantsyrev, A.S. Chuvatin, A.A. Esaulov, A.S. Safronova, L.I. Rudakov, A.L. Velikovich, K.M. Williamson, G.C. Osborne, I. Shrestha, M.E. Weller, V.V. Shlyaptseva, “Anisotropy of radiation emitted from planar wire arrays”, Phys. Plasmas 20, 070702 (2013).

6. N. L. Kugland , J. S. Ross , P.-Y. Chang , R. P. Drake , G. Fiksel , D. H. Froula , S. H. Glenzer, G. Gregori , M. Grosskopf , C. Huntington , M. Koenig , Y. Kuramitsu , C. Kuranz , M. C. Levy, E. Liang , D. Martinez , J. Meinecke , F. Miniati , T. Morita , A. Pelka , C. Plechaty , R. Presura, A. Ravasio , B. A. Remington , B. Reville , D. D. Ryutov , Y. Sakawa , A. Spitkovsky , H. Takabe , H.-S. Park, “Visualizing electromagnetic fields in laser-produced counter-streaming plasma experiments for collisionless shock laboratory astrophysics”, Phys. Plasmas 20, 056313 (2013).

7. R. Mishra, P. Leblanc, Y. Sentoku, M. S. Wei, and F. N. Beg, “Collisional particle-in-cell modeling for energy transport accompanied by atomic processes in dense plasmas”, Phys. Plasmas, 20, 072704 (2013).

8. G.C. Osborne, V.L. Kantsyrev, A.A. Esaulov, A.S. Safronova, M.E. Weller, I. Shrestha, K.M. Williamson, V.V. Shlyaptseva, “Implosion characteristics and applications of combined tungsten-aluminum Z-pinch planar arrays”, High Energy Density Physics 9, 653-660 (2013).

9. C.Plechaty, R. Presura, A.A.Esaulov, “Focusing of an Explosive Plasma Expansion in a Transverse Magnetic Fied”, Phys. Rev. Lett. 111, 185002 (2013).

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10. T. Yabuuchi, R. Mishra, C. McGuffey, B. Qiao, M. S. Wei, H. Sawada, Y. Sentoku, T. Ma, D. P. Higginson, K. U. Akli, D. Batani, H. Chen, L. A. Gizzi, M. H. Key, A. J. Mackinnon, H. S. McLean, P. A. Norreys, P. K. Patel, R. B. Stephens, Y. Ping, W. Theobald, C. Stoeckl, and F. N. Beg, “Impact of extended preplasma on energy coupling in kilojoule energy relativistic laser interaction with cone wire targets relevant to fast ignition”, New J. Phys., 15, 015020 (2013).

2013 Papers Submitted for Publication (8) 1. V. V. Ivanov, A. A. Anderson, D. Papp, B. R. Talbot, J. P. Chittenden, N. Niasse, I. A.

Begishev, “UV laser probing diagnostics for the dense Z pinch”, submitted to IEEE Trans. Plasma Sci. (2013).

2. V.L. Kantsyrev, A.S. Chuvatin, L.I. Rudakov, A.A. Esaulov, A.L. Velikovich, I. Shrestha, A.S. Safronova, V.V. Shlyaptseva, G.C. Osborne, A. Astanovitsky, M.E. Weller, S. Keim, A. Stafford, M.E. Cuneo, B. Jones, R.A. Vesey, “New Compact Hohlraum Configuration with Parallel Planar Wire Array X-ray Sources at the 1.7 MA Zebra Generator”, submitted to Phys. Rev. Lett. (2013).

3. V.L. Kantsyrev, A.S. Chuvatin, A.S. Safronova, L.I. Rudakov, A.A. Esaulov, A.L. Velikovich, I. Shrestha, A. Astanovitsky, G.C. Osborne, V.V. Shlyaptseva, M.E. Weller, S. Keim, A. Stafford, M. Cooper, “Radiation Sources with Planar Wire Arrays and Planar Foils for ICF and High Energy Density Physics Research”, Phys. Plasmas (accepted Nov. 2013).

4. Y. Paudel, N. Renard-Le Galloudec, Ph. Nicolai, E. d’Humieres, A. Ya. Faenov, V. L. Kantsyrev, A. S. Safronova, I. Shrestha, G. C. Osborne, V. V. Shlyaptseva, Y. Sentoku, “Proton fountain effect in high-intensity laser target interactions”, submitted to Phys.Plasmas (2013).

5. H.U. Rahman, F.J. Wessel, R. Presura, P. Ney, “High Gain Fusion in a Staged Z-pinch”, submitted to IEEE Trans. Plasma Sci. (2013).

6. A.S. Safronova, V.L. Kantsyrev, A.A. Esaulov, A.S. Chuvatin, M.E. Weller, V.V. Shlyaptseva, I. Shrestha, S.F. Keim, A. Stafford, C.A. Coverdale, J.P. Apruzese, N.D. Ouart, J.L.Giuliani, A.S. Chuvatin, “Radiation from mixed Multi-Planar Wire Arrays”, Phys. Plasmas (accepted Oct. 2013).

7. H. Sawada, M.S. Wei, S. Chawla, A. Morace, K. Akli, T. Yabuuchi, N. Nakanii, M.H. Key, P.K. Patel, A.J. Mackinnon, H.S. McLean, R.B. Stephens, F.N. Beg, “Investigation of fast electron –induced K α x-rays in laser-produced blow-off plasma”, submitted to Phys. Rev. E, ( 2013).

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8. M.E. Weller, A.S. Safronova, V.L. Kantsyrev, A.A. Esaulov, I. Shrestha, J.P. Apruzese, A.S. Chuvatin, A. Stafford, S.F. Keim, V.V. Shlyaptseva, G.C. Osborne, E.E. Petkov, “Radiation from Ag High Energy Density Z-pinch Plasmas with Applications to Lasing”, Phys. Plasmas (accepted Nov. 2013).

2013 Conference Proceedings (4) 1. A. Anderson, V. V. Ivanov, B. Talbot, D. Papp, “Study of ablation and implosion stages of 1

ma wire array z-pinches using uv laser diagnostics”, Proceedings of the IEEE Pulsed Power & Plasma Science, San Francisco, California, June 16-21, 2013, submitted.

2. V. T. Davis, D. D. Davis, K. Chartkunchand, J. S. Thompson, and A. M. Covington,

“Production Of SiOn- And (SiO2)n

-, n= 2, 3, 4 Molecular And Cluster Anion Beams From A Cesium-Sputter-Type Negative Ion Source,” 22nd International Conference on the Application of Accelerators in Research and Industry, AIP Conf. Proc. 1525, 251-254 (2013); doi 10.1063/1.4802329.

3. D. Papp, R. Presura, V. V. Ivanov, A. A. Anderson, M. S. Wallace, and B. R. Talbot, “2d

spatially resolved spectroscopic diagnostics using a single convex crystal”, Proceedings, 19th IEEE Pulsed Power Conference (PPC), doi: 10.1109/PPC.2013.6627631.

4. H.U. Rahman, F.J. Wessel, R. Presura, P. Ney, “High gain fusion in a Staged Z-pinch”, 19th

IEEE Pulsed Power Conference (PPC), 2013, doi: 10.1109/PPC.2013.6627562R. 2013 Invited Papers (1) 1. A.S. Safronova and V.L. Kantsyrev, “Z-pinch Research on Radiation, Atomic and Plasma

Physics”, Stewardship Science Academic Programs Annual, DOE/NA-0019, p. 7 (2013). Invited paper.

2013 Contributed Papers (2) 1. F.N. Beg, J. Chittenden, D. Mariscal, C.M. Mcguffey, M.S. Wei, Julio Cesar Valenzuela, R.

Presura, P. Wiewior, S. Haque and A. M. Covington, “Application of Proton Deflectometry to Z-Pinch Plasma Systems at the Mega-Ampere Scale”, submitted to 55th Annual Meeting of the APS Division of Plasma Physics, Denver, CO, (November 2013).

2. K. C. Chartkunchand, K. R. Carpenter, V. T. Davis, P. A. Neill, J. S. Thompson and A. M.

Covington, “Anion Photoelectron Distribution Measurements Near Threshold Utilizing Velocity-Map Imaging Spectroscopy”, submitted to ECAMP 11, Aarhus University, Denmark, (July 2013).

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2013 Invited Talks (12) 1. A.M. Covington, “An Overview of Recent Scientific Activity at the Nevada Terawatt

Facility”, 2013 Stewardship Science Academic Programs (SSAP) Symposium, NNSA/DOE, Albuquerque, NM, June 27-28, 2013. Invited talk.

2. V.V. Ivanov, “UV laser Diagnostics for the dense Z pinch”, 40th IEEE International Conference on Plasma Science (ICOPS), San Francisco, CA, June 16-21, 2013. Invited talk.

3. V.L. Kantsyrev, L.I. Rudakov, A.S. Chuvatin, A.S. Safronova, A.A. Esaulov,

A.L.Velikovich, I. Shrestha, K.M. Williamson, G.C. Osborne, V.V. Shlyaptseva, M.E. Weller, S.F. Keim, A. Stafford, “Planar wire arrays as a perspective source for radiation physics and ICF”, Symposium ”The Power of Plasma Theory: From Fusion Energy to the Cosmos”, University of California, San Diego, CA, May 4, 2013. Invited talk.

4. V.L. Kantsyrev, A.S. Chuvatin, A.S. Safronova, L.I. Rudakov, A.A. Esaulov, A.L.

Velikovich, I. Shrestha, A. Astanovitsky, G.C. Osborne, V.V. Shlyaptseva, M.E. Weller, S. Keim, A. Stafford, “Radiation Sources with Planar Wire Arrays for ICF and High Energy Density Physics Research”, International Workshop RHEDP 2013, Lake Tahoe, April 2-5, 2013. Invited talk.

5. N.D. Ouart, J.L. Giuliani, A. Dasgupta, A.S. Safronova, V.L. Kantsyrev, A.A. Esaulov, I.

Shrestha, M.E. Weller, V. Shlyaptseva, G.C. Osborne, A. Stafford, S. Keim, R.W. Clark, “Inner-shell radiation from Wire Array Implosions on the Zebra Generator”, International Workshop RHEDP 2013, Lake Tahoe, April 2-5, 2013. Invited talk.

6. R. Pandit, Y. Sentoku, “Spectral and Angular Distribution of Photons via Radiative

Damping in Super Intense Laser-Matter Interaction”, South Lake Tahoe, NV, RHED Conference, April 2-5, 2013. Invited talk.

7. A.S. Safronova, V.L. Kantsyrev, A.A. Esaulov, U. I. Safronova, V.V. Shlyaptseva, I.

Shrestha, G. C. Osborne, M.E. Weller, A. Stafford, S. F. Keim, M. Lorance, M. Cooper, A.S. Chuvatin, “Radiative Signatures of Z-pinch Plasmas at UNR: from X-Pinches to Wire Arrays”, International Conference on Plasma Science and Applications (ICPSA 2013), Singapore, Dec. 4-6, 2013. Invited talk.

8. A.S. Safronova, V.L. Kantsyrev, A.A. Esaulov, U. I. Safronova, I. Shrestha, V.V.

Shlyaptseva, M.E. Weller, G. C. Osborne, A. Stafford, S. F. Keim, E. E. Petkov, K. Schultz, M. Cooper, “Z-pinch Research on Radiation, Atomic and Plasma Physics”, 2013 Stewardship Science Academic Programs (SSAP) Symposium, NNSA/DOE, Albuquerque, NM, June 27-28, 2013. Invited talk.

9. A.S. Safronova, V.L. Kantsyrev, A.A. Esaulov, A.S. Chuvatin, M.E. Weller, V.V.

Shlyaptseva, I. Shrestha, S.F. Keim, A. Stafford, C.A. Coverdale, J.P. Apruzese, N.D. Ouart, J.L.Giuliani, A.S. Chuvatin, “Radiation from Multi-Planar Wire Arrays and Applications”, International Workshop RHEDP 2013, Lake Tahoe, April 2-5, 2013. Invited talk.

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10. I.Shrestha, V. L. Kantsyrev, A. S. Safronova, A. A. Esaulov, M. Nishio, V. V. Shlyaptseva, S. F. Keim, M.E. Weller, A. Stafford, “Investigation of Hard X-ray and Particle Beams in Zebra Experiments”, International Workshop RHEDP 2013, Lake Tahoe, April 2-5, 2013. Invited talk.

11. A.Stafford, A.S. Safronova, V.L. Kantsyrev, A.A. Esaulov, M.E. Weller, G.C. Osborne, I.

Shrestha, S.F. Keim, V.V. Shlyaptseva, C.A. Coverdale, A.S. Chuvatin, “Review of Recent Mid-Z Precursor Wire Array Experiments on the Zebra Generator at UNR”, International Workshop RHEDP 2013, Lake Tahoe, April 2-5, 2013. Invited talk.

12. M.E. Weller, A.S. Safronova, V.L. Kantsyrev, A.A. Esaulov, I. Shrestha, J.P. Apruzese, A.S.

Chuvatin, A. Stafford, S.F. Keim, V.V. Shlyaptseva, G.C. Osborne, E.E. Petkov, “Radiation from Ag High Energy Density Z-pinch Plasmas with Applications to Lasing”, International Workshop RHEDP 2013, Lake Tahoe, April 2-5, 2013. Invited talk.

2013 Contributed Talks (11) 1. V.L. Kantsyrev, A.S. Safronova, A.A. Esaulov, I. Shrestha, G.C. Osborne, V.V. Shlyaptseva,

M.E. Weller, H.A. Zunino, A.S. Chuvatin, L.I. Rudakov, A.L. Velikovich, B. Jones, R.A. Vesey, “Study of Implosion Dynamics and Radiative Mechanisms of Planar Foil Liners in Comparison with Planar Wire Arrays at 1.7 MA UNR Zebra Generator”, 40th IEEE International Conference on Plasma Science (ICOPS), San Francisco, CA, June 16-21, 2013.

2. D.Mariscal, C. McGuffey, J. Valenzuela, M. Wei, F. Beg, R. Presura, S. Haque, et al, “Application of Proton Deflectometry to Z-Pinch Plasma Systems at the Mega-Ampere Scale”, 55th Annual Meeting of the APS Division of Plasma Physics, Denver, CO, November 11 – 15, 2013.

3. P.Ney, H. Rahman, F. Wessel, R. Presura, “High gain fusion in a Staged Z-pinch”, 55th Annual Meeting of the APS Division of Plasma Physics, Denver, CO, November 11 – 15, 2013.

4. D. Papp, R. Presura, M. Wallace, B. Largent, S. Haque, A. Arias, V. Khanal, V. Ivanov, “2D x-ray imaging spectroscopic diagnostics using convex bent crystal”, 55th Annual Meeting of the APS Division of Plasma Physics, Denver, CO, November 11 – 15, 2013.

5. I.Paraschiv, Y. Sentoku, R. Mancini, and T. Johzaki, “Radiation transport in ultrafast heated high Z solid targets”, 55th Annual Meeting of the APS Division of Plasma Physics, Denver, CO, November 11 – 15, 2013.

6. H.U. Rahman, F.J. Wessel, P. Ney, R. Presura, “The role of shock waves in a Z-pinch”, 40th IEEE International Conference on Plasma Science (ICOPS), San Francisco, CA, June 16-21, 2013.

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7. A.S. Safronova, V.L. Kantsyrev, A.A. Esaulov, M.E. Weller, I. Shrestha, V.V. Shlyaptseva, A. Stafford, S.F. Keim, M. Lorance, A.S. Chuvatin, C. A. Coverdale, B. Jones,“ New Regimes of Implosions of Large Sized Wire Arrays With and Without Modified Central Plane at 1.5-1.7 MA ZEBRA”, 55th Annual Meeting of the APS Division of Plasma Physics, Denver, CO, Nov. 11-15, 2013.

8. A.S. Safronova, V.L. Kantsyrev, A.Y. Faenov, U.I. Safronova, P. Wiewior, A. Stafford, V.V. Shlyaptseva, P. Wilcox, I. Shrestha, Y. Paudel, “New Spectral Signatures of Hollow Fluorine Ions from Femtosecond Laser-produced Plasmas”, 11th International Colloquium on Atomic Spectra and Oscillator Strengths for Astrophysical and Laboratory Plasmas, Mons, Belgium, August 5-9, 2013.

9. A.S. Safronova, V.L. Kantsyrev, A.A. Esaulov, M.E. Weller, I. Shrestha, V.V. Shlyaptseva, A. Stafford, G. C. Osborne, S.F. Keim, E.E. Petkov, A.S. Chuvatin, C. A. Coverdale, B. Jones,“ Radiation Signature of Large Sized Multi-Planar Wire Arrays”, 55th Annual Meeting of the APS Division of Plasma Physics, Denver, CO, November 11 – 15, 2013.

10. I.Shrestha, V. L. Kantsyrev, A. S. Safronova, A. A. Esaulov, M. Nishio, V. V. Shlyaptseva, S. F. Keim, M.E. Weller, A. Stafford, E. Petkov, K. Schultz, M. Cooper, “Hard X-ray and Particle Beams research in 1.7 MA Z-pinch and Laser Plasma Experiments”, 55th Annual Meeting of the APS Division of Plasma Physics, Denver, CO, Nov. 11-15, 2013.

11. M.Wallace, N. Pereira, A. Kastengren, R. Presura, “Characterization of a quartz crystal for X-ray spectropolarimetric plasma diagnostics”, 55th Annual Meeting of the APS Division of Plasma Physics, Denver, CO, November 11 – 15, 2013.

2013 Poster Presentations (25) 1. A.Anderson, V. V. Ivanov, D. Papp, S. D. Altemara, “Study of Implosion in Wire Arrays

with UV interferometry and Faraday Rotation Diagnostics”, International Workshop RHEDP 2013, Lake Tahoe, April 2-5, 2013.

2. A.Arias, N. Quiros, V. Khanal, W. C. Wan, J. Meineke, N. L. Kugland, T. Morita, G. Gregori, H-S. Park, and R. Presura, "Laser-Plasma Density and Temperature Measurements with Triple Langmuir Probes", 55th Annual Meeting of the APS Division of Plasma Physics, Denver, CO, November 11 – 15, 2013.

3. S.Fuelling, B. S. Bauer, I. R. Lindemuth, R. E. Siemon, K. C. Yates , “Multiband Time-

Resolved Spectra of Metal Surface Plasmas: Comparison of Experiment with Plasma Spectroscopic Modeling” 40th IEEE International Conference on Plasma Science (ICOPS), San Francisco, CA, June 16-21, 2013

4. S.Fuelling, B. S. Bauer, I. R.Lindemuth, R. E. Siemon, K. C. Yates, “Comparison of

Modeled and Experimental EUV Spectra from Al Surface Plasma Generated by Pulsed Multi‐MG Magnetic Fields” International Workshop RHEDP 2013, Lake Tahoe, April 2-5, 2013.

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5. S.Haque, “Visible Spectroscopy of Z-Pinches for Magnetic Field Measurement”, International Workshop RHEDP 2013, Lake Tahoe, April 2-5, 2013.

6. S.Haque, M. S. Wallace, A. Arias, T. Morita, C. Plechaty, C. Huntington, D. Martinez, S. J. Ross, H-S. Park, and R. Presura, "Magnetic Field Measurement in Magnetized Laser Plasmas Using Zeeman Broadening Diagnostics", 55th Annual Meeting of the APS Division of Plasma Physics, Denver, CO, November 11 – 15, 2013.

7. M.C. Jo, V. Ivanov, S. Woolf, D. Tupa, “Laser safety practicum”, International Laser Safety Conference, 2013.

8. I.R. Lindemuth, R. E. Siemon, B. S. Bauer, W. L. Atchison, “Megagauss Magnetic Fields

and Surface Plasmas: Physical Insight, Computational Issues” 40th IEEE International Conference on Plasma Science (ICOPS), San Francisco, CA, June 16-21, 2013

9. R.Pandit, Y. Sentoku, “Spectrum and angular distribution of gamma-rays from radiative

damping in extremely relativistic laser-plasma interaction”, 55th Annual Meeting of the APS Division of Plasma Physics, Denver, CO, Nov 11- Nov 15, 2013.

10. D.Papp, V. V. Ivanov, R. Presura, A. A. Anderson, B. R. Talbot, “Developing Imaging

Spectroscopy of HED Plasmas Using a Single Convex Crystal”, International Workshop RHEDP 2013, Lake Tahoe, April 2-5, 2013.

11. D.Papp, V. V. Ivanov, R. Presura, A. A. Anderson, and B. R. Talbot, "2D spatially resovled

spectroscopy of hed plasmas using a single convex crystal", 40th IEEE International Conference on Plasma Science (ICOPS), San Francisco, CA, June 16-21, 2013.

12. I.Paraschiv and Y. Sentoku, “Radiation Transport in PIC Modeling of Laser Interactions

with High-Z Targets”, International Workshop RHEDP 2013, Lake Tahoe, April 2-5, 2013.

13. N.Pereira, M. Wallace, and R. Presura, "Extending crystal options in x-ray polarization splitting", 55th Annual Meeting of the APS Division of Plasma Physics, Denver, CO, November 11 – 15, 2013.

14. E.E. Petkov, M.E. Weller, A.S. Safronova, V.L. Kantsyrev, A.A. Esaulov, I. Shrestha, G.C.

Osborne, A. Stafford,V.V. Shlyapsteva, S.F. Keim, C. A. Coverdale, “Extreme Ultraviolet Spectroscopy of Cu Cylindrical Wire Arrays on zebra at UNR”, 40th IEEE International Conference on Plasma Science (ICOPS), San Francisco, CA, June 16-21, 2013.

15. C.Plechaty, C. Huntington, F. Fiuza, D. Ryutov, H.-S. Park, S. Ross, R. Presura, and B.

Remington, "HYDRA Simulations Relevant to Collisionless Shock Experiments to be Performed at NIF", 55th Annual Meeting of the APS Division of Plasma Physics, Denver, CO, November 11 – 15, 2013.

16. R.Presura, M. S. Wallace, S. Haque, A. Arias, and N. Quiros, "Energetic Electron Beams in

Conical Wire Array Z-Pinches", 55th Annual Meeting of the APS Division of Plasma Physics, Denver, CO, November 11 – 15, 2013.

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17. R.Presura, M. Wallace, S. Haque, N. Quiros, and A. Arias, "Electron beams and x-ray emission of conical wire array Z-pinches", 40th IEEE International Conference on Plasma Science (ICOPS), San Francisco, CA, June 16-21, 2013.

18. V.V. Shlyaptseva, V.L. Kantsyrev, A.S. Safronova, A.A. Esaulov, I. Shrestha. M. E. Weller, G.C. Osborne, S.F. Keim, “Gold Planar Wire Array Radiation Sources at University Scale Generators and Their Applications”, International Conference on Plasma Science and Applications (ICPSA 2013), Singapore, Dec. 4-6 (2013). “One of the best posters” award.

19. V.V. Shlyaptseva, A.S. Safronova, V.L. Kantsyrev, I. Shrestha, P. Wiewior, M.E. Weller, “Analysis and Comparison of Spectral Features of Stainless Steel X-pinches and Femtosecond Laser Flat Fe Target Experiments”, 11th International Colloquium on Atomic Spectra and Oscillator Strengths for Astrophysical and Laboratory Plasmas, Mons, Belgium, August 5-9, 2013.


Shrestha, S.F. Keim, V.V. Shlyaptseva, C.A. Coverdale, A.S. Chuvatin, “Review of Recent Mid-Z Precursor Wire Array Experiments on the Zebra Generator at UNR”, 2013 Stewardship Science Academic Programs (SSAP) Symposium, NNSA/DOE, Albuquerque, NM, June 27-28, 2013.


Shrestha, S.F. Keim, V.V. Shlyaptseva, C.A. Coverdale, A.S. Chuvatin, “Analysis of Al Precursor Wire Array Experiments at the 1 MA Zebra Generator at UNR”, 40th IEEE International Conference on Plasma Science (ICOPS), San Francisco, CA, Juny 16-21, 2013.

22. M.Wallace, N. R. Pereira, A. Kastengren, and R. Presura, "Characterization of a crystal for

x-ray spectropolarimetric plasma diagnostics", 40th IEEE International Conference on Plasma Science (ICOPS), San Francisco, CA, June 16-21, 2013.

23. M.Wallace, S. Haque, A. Arias, N. Quiros, R. Presura, “Faraday Cup Measurements of

Magnetically Deflected Electron Beams in X- and Z-Pinches”, International Workshop RHEDP 2013, Lake Tahoe, April 2-5, 2013.

24. M.E. Weller, A.S. Safronova, V.L. Kantsyrev, A.A. Esaulov, I. Shrestha, A. Stafford, S.

Keim, V.V. Shlyaptseva, G. C. Osborne, E. E. Petkov, J.P. Apruzese, J.L. Giuliani, A.S. Chuvatin, “Radiation from Ag High Energy Density Z-pinch Plasmas with Applications to Lasing”, 2013 Stewardship Science Academic Programs (SSAP) Symposium, NNSA/DOE, Albuquerque, NM, June 27-28, 2013.

25. K.C. Yates, B. S. Bauer, S. Fuelling, V. V. Ivanov, S. D. Altemara, D. Papp, A. A. Anderson,

G. A. Wurden, T. J. Awe, R. S. Bauer, “Plasma Formation and Evolution on a Copper Surface Driven by Mega-Ampere Current Pulse” 40th IEEE International Conference on Plasma Science (ICOPS), San Francisco, CA, June 16-21, 2013.

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YEAR 2012 2012 Publications (26) 1. S. D. Altemara, D. Papp, V. V. Ivanov, A. A. Anderson, A. A. Astanovitskiy, and V.

Nalajala, “High-Resolution UV Laser Diagnostics on the 1-MA Zebra Generator”, IEEE Trans. Plasma Sci., Dec 2012

2. S. N. Chen, E. d’Humie`res, E. Lefebvre, L. Romagnani, T. Toncian, P. Antici, P. Audebert,

E. Brambrink, C. A. Cecchetti, T. Kudyakov, A. Pipahl, Y. Sentoku, M. Borghesi, O. Willi, and J. Fuchs, "Focusing dynamics of high-energy density, laser-driven ion beams", Phys. Rev. Lett. 108, 055001 (2012).

3. J. Giuliani, F. N. Beg, R. M. Gilgenbach, V. L. Kantsyrev, B. Kusse, V. V. Ivanov, R.

Presura, “Pinch Research on University Pulsed Power Generators in the United States”, IEEE Trans. Plasma Sci. PP, 99, 1-19 (2012).

4. G. Hinojosa, A.M. Covington, G. Alna-Washi, M. Lu, R. A. Phaneuf, M.M. Sant’Anna, C.

Cisneros, I. Alvarez, A. Aguilar, A.L.D. Kilcoyne, A.S. Schlachter, C.P. Ballance and B. M. McLaughlin, “Valence-shell single photoionization of Kr+ions: Experiment and Theory”, Phys. Rev. A., 00 003400 (Nov 2012).

5. V. V. Ivanov, J. P. Chittenden, R. C. Mancini, D. Papp, N. Niasse, S. D. Altemara, and A. A.

Anderson, “Investigation of plasma instabilities in the stagnated Z pinch”, Phys. Rev. E, 86, 046403 (2012).

6. Y. Kitagawa, Y. Mori, O. Komeda, K. Ishii, R. Hanayama, K. Fujita, S. Okihara, T. Sekine,

N. Satoh, T. Kurita, M. Takagi, T. Kawashima, H. Kan, N. Nakamura, T. Kondo, M. Fujine, H. Azuma, T. Motohiro, T. Hioki, Y. Nishimura, A. Sunahara, and Y. Setnoku, "Fusion using fast heating of a compactly imploded CD core", Phys. Rev. Lett. 108, 155001 (2012).

7. N. L. Kugland, D. D. Ryutov, P.-Y. Chang, R. P. Drake, G. Fiksel, D. H. Froula, G. Gregori,

M. Grosskopf, M. Koenig, Y. Kuramitsu, C. Kuranz, M. C. Levy, E. Liang, J. Meinecke, F. Miniati, T. Morita, A. Pelka, C. Plechaty, R. Presura, A. Ravasio, B. A. Remington, B. Reville, J. S. Ross, Y. Sakawa, A. Spitkovsky, H. Takabe, H.-S. Park, “Self-organized electromagnetic field structures in laser-produced counterstreaming plasmas”, Nature Physics 8, 809-812 (2012).

8. T. Ma, H. Sawada, P.K. Patel, C.D. Chen, L. Divol, D.P. Higginson, A.J. Kemp, M.H. Key,

D.J. Larson, S. Le Pape, A. Link, A.G. MacPhee, H.S. McLean, Y. Ping, R.B. Stephens, S.C. Wilks, F.N. Beg, “Fast electron temperature and coupling efficiencies with preplasma for cone-guided Fast Ignition”, Phys. Rev. Lett., 108, 115004 (2012).

9. A. Nishida, N. Yugami, T. Higashiguchi, T. Otsuka, F. Suzuki, M. Nakata, Y. Sentoku, and

R. Kodama, "Experimental observation of frequency up-conversion by flash ionization", Applied Phys. Lett. 101, 16118 (2012).

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10. G.C. Osborne, V.L. Kantsyrev, A.S. Safronova, A.A. Esaulov, M.E. Weller, I. Shrestha, V.V. Shlyaptseva, and N. D. Ouart, ``X-ray absorption spectroscopy of aluminum z-pinch plasma with tungsten backlighter planar wire array source , Rev. Sci. Instrum. 83, 10E103 (2012).

11. N.D. Ouart, J.L. Giuliani, A.S. Safronova, V.L. Kantsyrev, A.A. Esaulov, N.R. Pereira, I. Shrestha, K.M. Williamson, G.C. Osborne, M.E. Weller, V. Shlyaptseva, “Time-gated measurements of electron beam generated Kα emission lines from brass planar wire array implosions”, High Energy Density Physics 8, 247-252 (2012).

12. R.R. Pandit, Y. Sentoku, “Higher order terms of radiative damping in extreme intense laser-

matter interaction”, Phys. Plasmas, 19, p. 073304, (2012). 13. D. Papp, V. V. Ivanov, B. Jones, A. Haboub, A. A. Anderson, S. D. Altemara, B. R. Talbot,

“Study of the precursor and non-precursor implosion regimes in wire array Z-pinches”, Phys. Plasmas, 19, 092704 (2012).

14. B. S. Paradkar, T. Yabuuchi, H. Sawada, D. P. Higginson, A. Link, M. S. Wei, R. B.

Stephens, S. I. Krasheninnikov, and F. N. Beg, “Emission of energetic protons from relativistic intensity laser interaction with a cone-wire target”, Phys. Rev. E 86, 056405 (2012).

15. Y. Paudel, N. Renard-Le Galloudec, E. d'Humieres, Ph. Nicolai, A. Ya. Faenov, V.L.

Kantsyrev, A.S. Safronova, I. Shrestha, G.C. Osborne, V.V. Shlyaptseva and Y. Sentoku, “Self-proton/ion radiography of laser-produced proton/ion beam from thin foil targets”, Phys. Plasmas 19, 123101 (2012).

16. Y. Ping, A. J. Kemp, L. Divol, M. H. Key, P. K. Patel, K. U. Akli, F. N. Beg, S. Chawla, C.

D. Chen, R. R. Freeman, D. Hey, D. P. Higginson, L. C. Jarrott, G. E. Kemp, A. Link, H. S. McLean, H. Sawada, R. B. Stephens, D. Turnbull, B. Westover, and S. C. Wilks, “Dynamics of Relativistic Laser-Plasma Interaction on Solid Targets”, Phys. Rev. Lett. 109, 145006, (2012).

17. R. Presura, “Hanle Effect as Candidate for Measuring Magnetic Fields in Laboratory

Plasmas”, Rev. Sci. Instrum. 83, 10D528 (2012). 18. H. U. Rahman, F. J. Wessel, P. Ney, R. Presura, Rahmat Ellahi, and P. K. Shukla, “Shock

Waves in a Z-pinch and the Formation of High Energy Density Plasma”, Phys. Plasmas 19, 122701 (2012).

19. J. S. Ross, S. H. Glenzer, P. Amendt, R. Berger, L. Divol, N. L. Kugland, O. L. Landen, C.

Plechaty, B. Remington, D. Ryutov, W. Rozmus, D. H. Froula, G. Fiksel, C. Sorce, Y. Kuramitsu, T. Morita, Y. Sakawa, H. Takabe, R. P. Drake, M. Grosskopf, C. Kuranz, G. Gregori, J. Meinecke, C. D. Murphy, M. Koenig, A. Pelka, A. Ravasio, T. Vinci, E. Liang, R. Presura, A. Spitkovsky, F. Miniati, and H.-S. Park, “Characterizing counter-streaming interpenetrating plasmas relevant to astrophysical collisionless shocks”, Phys. Plasmas 19, 056501 (2012).

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20. A.S. Safronova, V.L. Kantsyrev, A.A. Esaulov, I. Shrestha, V.V. Shlyaptseva, M.E. Weller, N.D. Ouart, G.C. Osborne, A. Stafford, S.F. Keim, A. L. Velikovich, J.L.Giuliani, A.S. Chuvatin, “Producing Kiloelectronvolt L-shell Plasmas on zebra at UNR”, IEEE Trans. Plasma Sci. 40, 3347 (2012).

21. A.S. Safronova, V.L. Kantsyrev, A.Y. Faenov, U.I. Safronova, P. Wiewior, N. Renard-Le

Galloudec, A.A. Esaulov, M.E. Weller, A. Stafford, P. Wilcox, I. Shrestha, N.D. Ouart, V. Shlyaptseva, G.C. Osborne, O. Chalyy, Y. Paudel, “Atomic physics of relativistic high-contrast laser-produced plasmas in experiments on leopard laser facility at UNR”, High Energy Density Physics 8, 190 (2012).

22. G. S. Sarkisov, V. V. Ivanov, P. Leblanc, Y. Sentoku, K. Yates, P. Wiewior, O. Chalyy, and

A. Astanovitskiy, V. Yu. Bychenkov, D. Jobe, and R. B Spielman, “Propagation of a laser-driven relativistic electron beam inside a solid dielectric”, Phys. Rev. E 86, 036412 (2012).

23. H. Sawada, D.P. Higginson, A. Link, T. Ma, S. C. Wilks, H.S. McLean, F. Perez, P.K. Patel,

and F.N. Beg, “Characterizing the energy distribution of laser-generated relativistic electrons in cone-wire targets”, Phys. Plasmas 19, 103108 (2012).

24. H. Sawada, T. Yabuuchi, S.P. Regan, K. Anderson, M.S. Wei, R. Betti, J. Hund, M.H. Key,

A.J. Mackinnon, H.S. McLean, R.R. Paguio, P.K. Patel, K.M. Saito, R.B. Stephens, S.C. Wilks, F.N. Beg, “Diagnosing Laser-Driven, Shock-Heated Foam Target with Al Absorption Spectroscopy on OMEGA EP”, High Energy Density Physics, 8, 180-183 (2012).

25. M.E. Weller, A.S. Safronova, V.L. Kantsyrev, A.A. Esaulov, C.A. Coverdale, A.S. Chuvatin,

N.D. Ouart, K.M. Williamson, I. Shrestha, G.C. Osborne, V.V. Shlyaptseva, S.F. Keim, A. Stafford, “Radiative properties of mixed nested cylindrical wire arrays on Zebra at UNR”, High Energy Density Physics 8, 184-189 (2012).

26. T. Yabuuchi, H. Sawada, S. P. Regan, K. Anderson, M. S. Wei, R. Betti, J. Hund, M. H. Key,

A. J. Mackinnon, H. S. McLean, R. R. Paguio, P. K. Patel, K. M. Saito, R. B. Stephens, S. C. Wilks, and F. N. Beg, “Temporally resolved characterization of shock-heated foam target with Al absorption spectroscopy for fast electron transport study”, Phys. Plasmas 19, 092705 (2012).

2012 Conference Proceedings (1) 1. A.Chuvatin, V. Kantsyrev, A. Astanovitsky, R. Presura, A. Safronova, B. LeGalloudec, V.

Nalajala, K. Williamson, I. Shrestha, G. Osborne, M. Weller, V. Shlyaptseva, L. Rudakov, M. Cuneo, “Advanced Load Current Multiplier on Zebra Generator”, Proceedings of the IEEE 18th Int. Pulsed Power Conference, pp. 975-982 (2012).

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2012 Invited Papers (4) 1. A.M. Covington, “Investigations of High Energy Density Plasmas at the Nevada Terawatt

Facility”, Invited Article, Center of Excellence Highlights, 2012 Stewardship Academic Alliance Annual Symposium, U.S. DOE National Nuclear Security Administration, DOE/NA-0018, Washington, DC, (Feb 2012). Invited paper.

2. J. L. Giuliani, F. N. Beg, R. M. Gilgenbach, V.L. Kantsyrev, B. R. Kusse, V. V. Ivanov, R. Presura, “Plasma Pinch Research on University Pulsed-Power Generators in the United States”, IEEE Trans. Plasma Sci. 40, 3246-3264 (2012). Invited paper.

3. V. Kantsyrev, “Study of a Prototype of New Hohlraum Configuration with Planar Wire Array X-ray Sources”, 2012 Stewardship Academic Alliance Annual Symposium, U.S. DOE National Nuclear Security Administration, DOE/NA-0018, Washington, DC, (Feb 2012). Invited paper.

4. A.S. Safronova, “Searching for Efficient X-ray Radiators for Wire Array Z-pinch Plasmas on Zebra at UNR”, 2012 Stewardship Academic Alliance Annual Symposium, U.S. DOE National Nuclear Security Administration, DOE/NA-0018, Washington, DC, (Feb 2012). Invited paper.

2012 Contributed Papers (8) 1. K. C. Chartkunchand, K. R. Carpenter, V. T. Davis, P. A. Neill, J. S. Thompson and A. M.

Covington, “Velocity-Map Imaging Spectroscopy of Negative Ion Photodetachement”, 44th EGAS Conference, Gothenborg Sweden, (July 2012).

2. K.C. Chartkunchand, K. R. Carpenter, V. T. Davis, P. A. Neill, J. S. Thompson, and A. M.

Covington, "Velocity-Map Imaging Spectroscopy of the Ge^{-}, Sn^{-},and Pb^{-} Negative Ions", 43rd DAMOP Conference, Orange County CA, (June 2012).

3. D. Mariscal, M.S. Wei, F.N. Beg, J.P. Chittenden, R. Presura, P. Wiewior and A. Covington,

“Investigations of Magnetic Fields in Wire Array Z-Pinches by Proton Deflectometry”, 39th IEEE International Conference on Plasma Science (ICOPS), Edinburgh, Scotland, UK, (July 2012).

4. Erik S. McKee, T.W. Darling and A.M. Covington, “Development of a Pulsed Neutron

Source and Neutron Diagnostics on Zebra”, 2012 Stewardship Academic Alliance Annual Symposium, U.S. DOE National Nuclear Security Administration, DOE/NA-0018, Washington D.C. (Feb 2012).

5. R. Pandit and Y. Sentoku, "Spectral and Angular Distribution of photons via Radiative

damping in super intense laser-matter interaction", 54th Annual Meeting of the APS Division of Plasma Physics, Providence, RI, October 29 – November 2, 2012.

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6. I.Paraschiv and Y. Sentoku, “Radiation transport in PIC modeling of laser interaction with high-Z targets”, Submitted to the 54th Annual Meeting of the APS Division of Plasma Physics, Providence, RI, October 29 – November 2, 2012.

7. Y. Paudel, N. Renard-Le Galloudec, V.L. Kantsyrev, A.S. Safronova, A.Ya. Faenov, I.

Shrestha, G.C. Osborne, V. V. Shlyaptseva, Y. Sentoku, “Hollowing and filamentation of proton beams in high-intensity laser plasma interactions”, 54th Annual Meeting of the APS Division of Plasma Physics, Providence, RI, October 29 – November 2, 2012.

8. V. Sotnikov, T. Kim, E. Mishin, W. Amatucci, G. Ganguli, E. Tejero, T.A. Mehlhorn, and I.

Paraschiv, “Low Frequency Plasma Turbulence as a Source of Clutterin Surveillance and Communication”, 13th Annual Advanced Maui Optical and Space Surveillance Technologies Conference, Maui, Hawaii, (September 2012).

2012 Invited Talks (5) 1. A.M. Covington, “Investigations of High Energy Density Plasmas at the Nevada Terawatt

Facility”, Center of Excellence Highlights, Stewardship Academic Alliance Annual, U.S. DOE National Nuclear Security Administration, DOE/NA-0018, Washington, DC, (Feb 2012). Invited talk.

2. V.L. Kantsyrev, A.S. Chuvatin, L.I. Rudakov, A.S. Safronova, A.A. Esaulov, A.L. Velikovich, A.L. Astanovitsky, I. Shrestha, G.C. Osborne, V. Nalajala, V.V. Shlyaptseva, M.E. Weller, S.F. Keim, A. Stafford, “Study of prototype of new hohlraum configuration with planar wire array x-ray sources”, 2012 Stewardship Science Academic Alliances (SSAA) Symposium, NNSA/DOE, Washington DC, (Feb 2012). Invited talk.

3. R. Presura, “Laboratory diagnostics primer for astronomers”, 9th Int. Conf. on High Energy

Density Laboratory Astrophysics, Tallahassee, FL, Apr. 30 – May 4, 2012. Invited talk. 4. A.S. Safronova, A.A. Esaulov, U.I. Safronova, M.E. Weller, P.G. Wilcox, A. Stafford, H.

Zunino, V.L. Kantsyrev, I. Shrestha, G.C. Osborne, V. Shlyaptseva, S.F. Keim, N.D. Ouart, “Theoretical X-ray/EUV Spectroscopy and Imaging Studies of Wire Arrays and X-pinch Plasmas”, 2012 Stewardship Science Academic Alliances (SSAA) Symposium, NNSA/DOE, Washington DC, (Feb 2012). Invited talk.

5. H. Sawada, “Spectra of laser generated relativistic electrons using cone-wire target”, 54th

Annual Meeting of the APS Division of Plasma Physics, Providence, RI, October 2012. Invited talk.

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2012 Contributed Talks (12) 1. S.Altemara, A. Anderson, D. Papp, V. Ivanov, “Development of UV Two-Frame Imaging

Diagnostics for Investigation of Plasma Dynamics in Z Pinches at Stagnation”, 54th Annual Meeting of the Division of Plasma Physics, Providence, RI, October 29-November 2, 2012.

2. V.V. Ivanov, J.P. Chittenden, R.C. Mancini, D. Papp, N. Niasse, A.A. Andersen, S.D. Altemara, “Study of instabilities in wire-array Z pinches at stagnation”, 54th Annual Meeting of the Division of Plasma Physics, Providence, RI, Oct. 29-Nov. 2, 2012.

3. V.L. Kantsyrev, A.S. Safronova, A.A. Esaulov, I. Shrestha, G.C. Osborne, V.V. Shlyaptseva, M.E. Weller, H.A. Zunino, A.S. Chuvatin, L.I. Rudakov, A.L. Velikovich, B. Jones, R.A. Vesey, “Study of a Prototype of a New Compact Hohlraum Configuration at the 1.7 MA UNR Zebra Generator”, 39th IEEE International Conference on Plasma Science (ICOPS), Edinburgh, Scotland, UK, July 8-12, 2012.

4. V.L. Kantsyrev, A.S. Chuvatin, L.I. Rudakov, A.S. Safronova, A.A. Esaulov, I. Shrestha,

G.C. Osborne, V.V. Shlyaptseva, M.E. Weller, S.F. Keim, A. Stafford, B. Jones, R. A. Vesey, “Experiments and Numerical Simulation on a New Hohlraum Configuration with Planar Wire Array Sources at the 1.7 MA Zebra Generator”, 54th Annual Meeting of the APS Division of Plasma Physics, Providence, RI, October 29-November 2, 2012.

5. N.D. Ouart, J.L. Giuliani, A. Dasgupta, A.S. Safronova, V.L.Kantsyrev, A.A. Esaulov, I.

Shrestha, M.E. Weller, V.V. Shlyaptseva, G.C. Osborne, A. Stafford, S.F. Keim, R.W. Clark, “Simultaneous time-gated measurements of K- and L-shell radiation from brass wire array implosions on Zebra”, 54th Annual Meeting of the APS Division of Plasma Physics, Providence, RI, October 29-November 2, 2012.

6. Y.Paudel, N. Renard-Le Galloudec, V.L.Kantsyrev, A.S. Safronova, A.Ya. Faenov, I.

Shrestha, G.C. Osborne, V.V. Shlyaptseva, Y. Sentoku, “Hollowing and filamentation of proton beams in high-intensity laser plasma interactions”, 54th Annual Meeting of the APS Division of Plasma Physics, Providence, RI, October 29-November 2, 2012.

7. A.S. Safronova, A.A. Esaulov, V.L. Kantsyrev, A. Stafford, M.E. Weller, V.V. Shlyaptseva,

H.A. Zunino, I. Shrestha, G. C. Osborne, S.F. Keim, A.S. Chuvatin, C. A. Coverdale, “ Implosions of Larger Size Wire Arrays at Enhanced Current of 1.5-1.7 MA on Zebra with LCM”, 39th IEEE International Conference on Plasma Science (ICOPS), Edinburgh, Scotland, UK, July 8-12, 2012.

8. A.S. Safronova, A.A. Esaulov, V.L. Kantsyrev, A.S. Chuvatin, C.A. Coverdale, B. Jones,

V.V. Shlyaptseva, M.E. Weller, A. Stafford, I. Shrestha, G.C. Osborne, S.F. Keim, “Larger Size Planar Wire Arrays with a Modified Central Plane and Their Applications on Zebra with LCM”, 54th Annual Meeting of the APS Division of Plasma Physics, Providence, RI, October 29-November 2, 2012.

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9. G.S. Sarkisov, V. Ivanov, Y. Sentoku, K. Yates, Ph. Leblanc, P. Wiewior, V. Bychenkov, D. Jobe, R. Spielman, “Laser-Driven Relativistic Electron Beam Interaction with Solid Dielectric”, International High Power Laser Ablation Conference, Santa Fe, NM, USA, May 2012.

10. A.Stafford, A.S. Safronova, V.L. Kantsyrev, A.A. Esaulov, M.E. Weller, I. Shrestha, G.C. Osborne, V.V. Shlyaptseva, S.F. Keim, C.A. Coverdale, A.S. Chuvatin, “Analysis of Precursor Properties of mixed Al/Alumel Cylindrical Wire Arrays”, 54th Annual Meeting of the APS Division of Plasma Physics, Providence, RI, October 29-November 2, 2012.

11. M.E. Weller, A.S. Safronova, V.L. Kantsyrev, A.A. Esaulov, A. Stafford, I. Shrestha, G. C.

Osborne, V.V. Shlyaptseva, S.F. Keim, H.A. Zunino, A.S. Chuvatin, J.P. Apruzese, I.E. Golovkin, J.J. MacFarlane, “Analysis of Radiation from Siver HED Plasma Sources with the Potential for Lasing”, 39th IEEE International Conference on Plasma Science (ICOPS), Edinburgh, Scotland, UK, July 8-12, 2012.

12. M.E. Weller, A.S. Safronova, V.L. Kantsyrev, A.A. Esaulov, I. Shrestha, G. C. Osborne,

V.V. Shlyaptseva, S.F. Keim, A. Stafford, E.E. Petkov, A.S. Chuvatin, J.P. Apruzese, I.E. Golovkin, J.J. MacFarlane, “Theoretical Investigation of Radiation Characteristics of Silver Z-pinch Arrays with Applications”, 54th Annual Meeting of the APS Division of Plasma Physics, Providence, RI, October 29-November 2, 2012.

2012 Poster Presentations (14) 1. A.Anderson, V. V. Ivanov, D. Papp, S. D. Altemara, “Study of Implosion in Wire Arrays

with UV interferometry and Faraday Rotation Diagnostics”, 54th Annual Meeting of the APS Division of Plasma Physics, Providence, RI, October 29-November 2, 2012.

2. V.L. Kantsyrev, A.S. Safronova, U.I. Safronova, I. Shrestha, M.E. Weller, G.C.Osborne,

V.V.Shlyaptseva, P.G. Wilcox, A. Stafford, “Advances in experimental spectroscopy of Z-pinch plasmas and applications”, 43nd Annual Meeting of the APS Division of Atomic, Molecular, and Optical Physics, Anaheim, California, June 6-8, 2012.

3. G.C. Osborne, V.L. Kantsyrev, A.S. Safronova, A.A. Esaulov, M.E. Weller, I. Shrestha, V.V.

Shlyaptseva, S.F. Keim, “Combined Tungsten-Aluminum Single Planar Wire Array Studies and Applications to Pulse Shaping and Absorption Spectroscopy”, 2012 Stewardship Science Academic Alliances (SSAA) Symposium, NNSA/DOE, Washington DC, February 22-23, 2012.

4. G.C. Osborne, V. L. Kantsyrev, A. S. Safronova, A. A. Esaulov, M. E. Weller, I. Shrestha, V.

V. Shlyaptseva, and N. D. Ouart, ``X-ray absorption spectroscopy of aluminum z-pinch plasma with tungsten backlighter planar wire array source’’, 19th Topical Conference on High-Temperature Plasma Diagnostics, Monterey, CA, May 6-10, 2012.

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5. N.D. Ouart, J.L. Giuliani, A. Dasgupta, A.S. Safronova, V.L.Kantsyrev, A.A. Esaulov, I. Shrestha, M.E. Weller, V.V. Shlyaptseva, G.C. Osborne, A. Stafford, S.F. Keim, R.W. Clark, “Simultaneous time-gated measurements of K- and L-shell radiation from brass wire array implosions on Zebra”, 54th Annual Meeting of the APS Division of Plasma Physics, Providence, RI, October 29-November 2, 2012.

6. R.Pandit, Y. Sentoku, “Spectral and Angular Distribution of Photons via Radiative

Damping in Super Intense Laser-Matter Interaction”, 54th Annual Meeting of the APS Division of Plasma Physics, Providence, RI, Oct 29 - Nov 2, 2012.

7. D.Papp, V. V. Ivanov, P. Hakel, R. C. Mancini, S. D. Altemara, A. A. Anderson,

“Investigation of K-shell radiation from two-component wire arrays”, 54th Annual Meeting of the Division of Plasma Physics, Providence, Rhode Island, October 29-November 2, 2012.

8. I.Paraschiv and Y. Sentoku, “Radiation transport in PIC modeling of laser interaction with

high-Z targets”, 54th Annual Meeting of the APS Division of Plasma Physics, Providence, Rhode Island, October 29 – November 2, 2012.

9. Y.Paudel, N. Renard-Le Galloudec, V.L.Kantsyrev, A.S. Safronova, A.Ya. Faenov, I. Shrestha, G.C. Osborne, V.V. Shlyaptseva, Y. Sentoku, “Hollowing and filamentation of proton beams in high-intensity laser plasma interactions”, 54th Annual Meeting of the APS Division of Plasma Physics, Providence, RI, October 29-November 2, 2012.


Shrestha, V.V. Shlyaptseva, S.F. Keim, “Analysis of Mg Spectra Produced on the Leopard Laser and Mid-Atomic Number Precursor Experiments on the Zebra Generator at UNR”, 2012 Stewardship Science Academic Alliances (SSAA) Symposium, NNSA/DOE, Washington DC, February 22-23, 2012.

11. A.Stafford, A.S. Safronova, V.L. Kantsyrev, A.A. Esaulov, M.E. Weller, I. Shrestha, G.C.

Osborne, V.V. Shlyaptseva, S.F. Keim, C.A. Coverdale, A.S. Chuvatin, “Analysis of Precursor Properties of mixed Al/Alumel Cylindrical Wire Arrays”, 54th Annual Meeting of the APS Division of Plasma Physics, Providence, RI, October 29-November 2, 2012.

12. M.E. Weller, A.S. Safronova, V.L. Kantsyrev, A.A. Esaulov, I. Shrestha, G.C. Osborne, V.V.

Shlyaptseva, S. Keim, A. Stafford, “Progress on Studying Radiation from Mixed Wire Arrays and New Data of Time-Gated Ag”, 2012 Stewardship Science Academic Alliances (SSAA) Symposium, NNSA/DOE, Washington DC, February 22-23, 2012.

13. M.E. Weller, A. S. Safronova, J. Clementson, V. L. Kantsyrev, U. I. Safronova, P. Beiersdorfer, E. E. Petkov, P. G. Wilcox, and G. C. Osborne, “Extreme ultraviolet spectroscopy and modeling of Cu on the SSPX Spheromak and laser plasma “Sparky”, 19th Topical Conference on High-Temperature Plasma Diagnostics, Monterey, CA, May 6-10, 2012.

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14. M.E. Weller, A.S. Safronova, V.L. Kantsyrev, A.A. Esaulov, A. Stafford, I. Shrestha, G. C. Osborne, V.V. Shlyaptseva, S.F. Keim, H.A. Zunino, A.S. Chuvatin, J.P. Apruzese, I.E. Golovkin, J.J. MacFarlane, “Analysis of Radiation from Siver HED Plasma Sources with the Potential for Lasing”, 39th IEEE International Conference on Plasma Science (ICOPS), Edinburgh, Scotland, UK, July 8-12, 2012.

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YEAR 2011

2011 Publications (14) 1. P. Antici, A. Mancic, M. Nakatsutsumi, P. Audebert, E. Brambrink, S. Gaillard, W. Nazarov

and J. Fuchs, “Tests of Proton Laser-acceleration Using Circular Laser Polarization, Foams and half Gas-bag Targets,” Plasma Physics and Controlled Fusion 53, 014002 (January 2011).

2. T.J. Awe, B. Bauer, S. Fuelling and R. E. Siemon, “The Evolving Structure of Plasma

Formed From the Surface of Aluminum Rods Driven to Megaampere Current,” IEEE Trans. Plasma Sci. 39, 2418-2419 (November 2011).

3. S.A. Gaillard, T. Kluge, K. A. Flippo, M. Bussmann, B. Gall, T. Lockard, M. Geissel, D. T.

Offermann, M. Schollmeier, Y. Sentoku and T. E. Cowan, “Increased laser-accelerated proton energies via direct laser-light-pressure acceleration of electrons in microcone targets,” Phys. Plasmas 18, 056710 (May 2011).

4. M.F. Gharaibeh, A. Aguilar, A. M. Covington, E. D. Emmons, S. W. Scully, R. A. Phaneuf,

A. Muller, J. D. Bozek, A. L. D. Kilcoyne, A. S. Schlachter, I. A`lvarez, C. Cisneros and G. Hinojosa, “Photoionization measurements for the iron isonuclear sequence Fe3+, Fe5+, and Fe7+,” Phys. Rev. A, Atomic, Molecular, and Optical Physics 83, 043412 (April 2011).

5. V.V. Ivanov, P. Hakel, R. C. Mancini, J. P. Chittenden, A. Anderson, T. Durmaz, P.

Wiewior, D. Papp, S. D. Altemara, A. L. Astanovitskiy and O. Chalyy, “Measurement of the Ionization State and Electron Temperature of Plasma during the Ablation Stage of a Wire-Array Z Pinch Using Absorption Spectroscopy,” Phys. Rev. Lett. 106 , 225005 (June 2011).

6. V.V. Ivanov , P. Hakel, R. C. Mancini, J. P. Chittenden, A. Anderson, A. P. Shevelko, P.

Wiewior, T. Durmaz, S. D. Altemara, D. Papp, A. L. Astanovitskiy, V. Nalajala, O. Chalyy and O. Dmitriev, “X-ray absorption spectroscopy for wire-array Z-pinches at the non-radiative stage,”. High Energy Density Physics 7, 383-390 (August 2011).

7. V.V. Ivanov, J. P. Chittenden, S. D. Altemara, N. Niasse, P. Hakel, R. C. Mancini, D. Papp

and A. A. Anderson, “Study of the Internal Structure and Small-Scale Instabilities in the Dense Z Pinch,” Phys. Rev. Lett. 107, 165002 (October 2011).

8. V.L. Kantsyrev, A. A. Esaulov, A. S. Safronova, A. L. Velikovich, L. I. Rudakov, G. C. Osborne, I. Shrestha, M. E. Weller, K. M. Williamson, A. Stafford and V. V. Shlyaptseva, “Influence of induced axial magnetic field on plasma dynamics and radiative characteristics of Z pinches,” Phys. Rev. E, Statistical, Nonlinear, and Soft Matter Physics 84, 046408 (October 2011).

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http://publish.aps.org/search/field/author/Hakel_P

9. N.R. Le Galloudec, J. Cobble, S. L. Nelson, A. Merwin, Y. Paudel, I. Shrestha, G. C. Osborne, K. M. Williamson and V. L. Kantsyrev, “Advantages of a soft protective layer for good signal-to-noise ratio proton radiographs in high debris environments,” High Energy Density Physics 7, 247-251 (December 2011).

10. A.S. Safronova, , A. A. Esaulov, V. L. Kantsyrev, N. D. Ouart, V. Shlyaptseva, M. E. Weller,

S.F. Keim, K. M. Williamson, I. Shrestha and G. C. Osborne, “Searching for efficient X-ray radiators for wire array Z-pinch plasmas using mid-atomic-number single planar wire arrays on Zebra at UNR,” High Energy Density Physics 7, 252-258 (May 2011).

11. G.S. Sarkisov, P. Leblanc, V. V. Ivanov, Y. Sentoku, V. Yu. Bychenkov, K. Yates, P.

Wiewior, D. Jobe and R. Spielman, “Fountain effect of laser-driven relativistic electrons inside a solid dielectric,” Applied Physics Letters 99, 131501 (September 2011).

12. Y. Sentoku, E. d'Humie`res, L. Romagnani, P. Audebert and J. Fuchs, “Dynamic Control

over Mega-Ampere Electron Currents in Metals Using Ionization-Driven Resistive Magnetic Fields,” Phys. Rev. Lett. 107, 135005 (September 2011).

13. K.M. Williamson, V. L. Kantsyrev, A. S. Safronova, P. G. Wilcox, W. Cline, S. Batie, B. Le

Galloudec, V. Nalajala and A. Astanovitsky, “Grazing incidence extreme ultraviolet spectrometer fielded with time resolution in a hostile Z-pinch environment,” Rev. Sci. Instrum. 82, 093506 (Sept. 2011).

14. M.F. Yilmaz, A. S. Safronova, V. L. Kantsyrev, A. A. Esaulov, K. M. Williamson, .R K.

Shrestha, M. E. Weller, G. C. Osborne and V. V. Shlyaptseva, “Modeling of K-shell Al and Mg radiation from compact single, double planar and cylindrical alloyed Al wire array plasmas produced on the 1 MA Zebra generator at UNR,” High Energy Density Physics 8, 30-37 (October 2011).

2011 Conference Proceedings (3) 1. V.V. Ivanov, P. Hakel, R. C. Mancini, J. P. Chittenden, A. P. Shevelko, P. Wiewior, S. D.

Altemara, A. Anderson, D. Papp, T. Durmaz, N. Niasse, A. L. Astanovitskiy, O. Chalyy, E. McKee, “Study of Wire-Array Z Pinches with UV Laser Diagnostics and Absorption Spectroscopy”, Proceedings of the 8th international conference on Dense Z-pinches, Biarritz, France, June 5-9, 2011, submitted

2. D.Papp, V. V. Ivanov, B. Jones, A. Haboub, A. A. Anderson, S. D. Altemara, J. P. Chittenden, “The Study of Ablation and Implosion Dynamics in Closely Coupled Nested Cylindrical and Star Wire Array Z-Pinches”, Proceedings of the 8th international conference on Dense Z-pinches, Biarritz, France, June 5-9, 2011, submitted

3. R.K. Bista, R. F. Bruch and A. M.Covington, “Vibrational spectroscopic methods to

characterize the bionanoparticles originating from newly developed self-forming synthetic PEGylated lipids (QuSomes),” Proceedings of the SPIE - The International Society for Optical Engineering 2011, 7908, 20110124 (2011).

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2011 Invited Papers (1) 1. A.Covington, et. al, “HEDP Physics at the Nevada Terawatt Facility”, Center of Excellence

Highlights, Stewardship Science Academic Alliance Annual Report, U.S. DOE National Nuclear Security Administration, Washington, DC, Feb 2011. Invited article.

2011 Invited Talks (9) 1. A.Chuvatin, V. Kantsyrev, A. Astanovitsky, R. Presura, A. Safronova, B. Le Galloudec, V.

Nalajala, K. Williamson, I. Shrestha, G. Osborne, M. Weller, V. Shlyaptseva, M. Cuneo and L. Rudakov, “Advanced Load Current Multiplier on Zebra Generator” , 18th IEEE International Pulsed Power Conference, Chicago, IL, June 19 - 23, 2011. Invited talk.

2. V.V. Ivanov “Study of Wire-Array Z-Pinches with UV Laser Diagnostics and Absorption

Spectroscopy”, 8th international conference on Dense Z-pinches, Biarritz, France, June 5-9, 2011. Invited talk.

3. V.L. Kantsyrev, A.A. Esaulov, K.M. Williamson, I. Shrestha, G.C. Osborne, V.V. Shlyaptseva, A.S. Safronova, M.F. Yilmaz, N.D. Ouart, M.E. Weller, P.G. Cox, L.I. Rudakov, A.L. Velikovich, A.S. Chuvatin, “Innovative approach for enhancing shaped x-ray production in Z-pinches (Experimental Studies of Implosion Characteristics and Radiation Properties of Planar and Cylindrical Wire Arrays and X-pinches)”, NNSA / 2011 Stewardship Science Academic Alliances Symposium, Washington, DC, Feb 2011. Invited talk.

4. V.L. Kantsyrev, A.S. Safronova, A.A. Esaulov, L.I. Rudakov, A.S. Chuvatin, A.L.

Velikovich, I. Shrestha, K.M. Williamson, G.C. Osborne, V.V. Shlyaptseva, N.D. Ouart, M.E. Weller, P. Wilcox, A. Stafford, S.F. Keim, “Radiative Properties of Wire Array Plasmas and Applications”, International Workshop on Radiation from High Energy Density Plasmas (RHEDP) , Reno, NV, Mar 2011. Invited talk.

5. N.D. Ouart, J.L. Giuliani, A.S. Safronova, V.L. Kantsyrev, A.A. Esaulov, N.R. Pereira, I. Shrestha, K.M. Williamson, G.C. Osborne, M.E. Weller, V. Shlyaptseva, “Cold K-shell Emission from the Implosion of Brass Wire Loads Performed at the 1-MA Zebra Generator at UNR”, International Workshop on Radiation from High Energy Density Plasmas (RHEDP) , Reno, NV, Mar, 2011. Invited talk.

6. A.S. Safronova, A.A. Esaulov, U.I. Safronova, W.R. Johnson, A.Ya. Faenov, N.D. Ouart, M.E. Weller, A. Stafford, P.G. Cox, S. F. Keim, G.C. Osborne, V.L. Kantsyrev, I. Shrestha, K.M. Williamson, G.C. Osborne, V. Shlyaptseva, P. Wiewior, N. Renard-LeGalloudec, Y. Paudel, “Theoretical X-ray/EUV Spectroscopy and Imaging Studies of Wire Array and X-pinch Plasmas”, NNSA / 2011 Stewardship Science Academic Alliances Symposium, Washington, DC, Feb 2011. Invited talk.

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7. A.S. Safronova, V.L. Kantsyrev, A.A. Esaulov, N.D. Ouart , M.F. Yilmaz, M.E. Weller, I. Shrestha , K.W. Williamson, P.G. Wilcox, A. Stafford, V. Shlyaptseva, G.C. Osborne, S.F. Keim, H. Zunino, A.S. Chuvatin, ” Studying Radiation from HED Wire Array and X-pinch Plasmas”, DOE/NNSA, Washington, DC, Nov 2011. Invited talk.

8. A.S. Safronova, V.L. Kantsyrev, A.Y. Faenov, U.I. Safronova, P. Wiewior, N. Renard-Le Galloudec, A.A. Esaulov, M.E. Weller, A. Stafford, P. Wilcox, I. Shrestha, N.D. Ouart, V. Shlyaptseva, G.C. Osborne, O. Chalyy, Y. Paudel, “Atomic Physics of Relativistic High-Contrast Laser-produced Plasmas in Experiments on Leopard Laser Facility at UNR”, International Workshop on Radiation from High Energy Density Plasmas (RHEDP), Reno, NV, Mar 2011. Invited talk.

9. M.E. Weller, A.S. Safronova, V.L. Kantsyrev, A.A. Esaulov, C.A. Coverdale, N.D. Ouart, K.M. Williamson, I. Shrestha, G.C. Osborne, V. Shlyaptseva, S. Keim, A. Stafford,”Radiative Properties of Mixed Nested Cylindrical Wire Arrays on Zebra at UNR”, International Workshop on Radiation from High Energy Density Plasmas (RHEDP) , Reno, NV, Mar 2011. Invited talk.

2011 Contributed Talks (11) 1. V.L. Kantsyrev, A.S. Safronova, A.A. Esaulov, A.S. Chuvatin, L.I. Rudakov, A.L.

Velikovich, K.M. Williamson, I. Shrestha, G.C. Osborne, M.E. Weller, V.V. Shlyaptseva, N.D. Ouart, A. Stafford, S. Keim, “Yield enhancement and x-ray pulse shaping of radiation from anisotropic wire array plasma sources”, 8th International Conference on Dense Z-pinches, Biarritz, France, Jun 2011.

2. V.L. Kantsyrev, A. A. Esaulov, A. S. Safronova, L. I. Rudakov, A. S. Chuvatin, A. L.

Velikovich, K. M. Williamson, G. C. Osborne, I. Shrestha, M. E. Weller, V. V. Shlyaptseva, A. Stafford, “Anisotropy and Pulse Shaping of Radiation Emitted from Multi-Planar Wire Arrays”, 38th International Conference on Plasma Science, Chicago, IL, Jun 2011.

3. V.L. Kantsyrev, A.S. Chuvatin, L.I. Rudakov, A.S. Safronova, A.A. Esaulov, G.C. Osborne,

I. Shrestha, V. V. Shlyaptseva, H. A. Zunino, M.E. Weller, A. Stafford, S. Keim, “Experimental Comparison of Radiative Characteristics and Implosion Dynamics of Planar Foils and Single Planar Wire Arrays in Current Region 0.9-1.6 MA on the UNR Zebra generator”, 53rd Annual Meeting of the Division of Plasma Physics, Salt Lake City, UT, Nov 2011.

4. G.Osborne, V. Kantsyrev, A. Esaulov, A. Safronova, M. Weller, I. Shrestha, K. Williamson, V. Shlyaptseva, “X-Ray Pulse Shaping from Tungsten-Based Multi-Planar Wire Arrays”, 38th International Conference on Plasma Science, Chicago, IL, Jun 2011.

5. N.D. Ouart, J. L. Giuliani, A. S. Safronova, V. L. Kantsyrev, A. A. Esaulov, N. R. Pereira, I.

Shrestha, K. M. Williamson, G. C. Osborne, M. E. Weller, V. Shlyaptseva, “Cold K-Shell Emission from the Implosion of Brass Planar Wire Arrays and X-Pinches Performed at the 1-MA Zebra Generator at UNR”, 38th International Conference on Plasma Science, Chicago, IL, Jun 2011.

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6. A.S. Safronova, V.L. Kantsyrev, A.A. Esaulov, I. Shrestha, V.V. Shlyaptseva, M.E. Weller, ,

N.D. Ouart, G.C. Osborne, K.M. Williamson, S. Keim, A.L. Velikovich, J.L. Giuliani, “Producing keV plasmas on Zebra at UNR: achievements, challenges and applications”, 8th International Conference on Dense Z-pinches, Biarritz, France, Jun 2011.

7. A.S. Safronova, V. L. Kantsyrev, A. A. Esaulov, M. E. Weller, V. V. Shlyaptseva, A.

Stafford, S. F. Keim, I. Shrestha, G. C. Osborne, K. M. Williamson, C. A. Coverdale, L. I. Rudakov, “Time Evolution of Z-Pinch Dynamics and Radiative Characteristics of Wire Arrays on Zebra at UNR”, 38th International Conference on Plasma Science, Chicago, IL, Jun 2011.

8. A.S. Safronova, V.L. Kantsyrev, I. Shrestha, V. V. Shlyaptseva, M.E. Weller, G.C. Osborne,

K.M. Williamson, A. Stafford, S. F. Keim, A.Ya. Faenov, A.A. Esaulov, P. Wiewior, N. Le Galloudec, Y. Paudel, , C.A. Coverdale, A.S. Chuvatin,” Analysis of Radiation from Implosions of Stainless Steel Wire Arrays on Zebra and Comparison with Results of High-Intensity Laser Flat Fe Target Experiments on Leopard at UNR”, 53rd Annual Meeting of the Division of Plasma Physics, Salt Lake City, UT, Nov 2011.

9. I.K. Shrestha, V. L. Kantsyrev, A. S. Safronova, A. A. Esaulov, A. Astanovitskiy, K. M.

Williamson, G. C. Osborne, M. E. Weller, V. V. Shlyaptseva, N. D. Ouart, “The Impact of Load Configuration and Wire Material on Radiation Yield from Wire Array Plasmas at University Scale Z-Pinch Pulsed Power Generators”, 18th IEEE International Pulsed Power Conference, Chicago, IL, Jun 2011.

10. M.E. Weller, A.S. Safronova, V.L. Kantsyrev, A.A. Esaulov, N.D. Ouart, K.M. Williamson,

I. Shrestha, G. C. Osborne, V.V. Shlyaptseva, “Analysis of Implosion Dynamics and Radiation of Mixed Mo and Al Triple Planar Wire Arrays With Different Inter-row Gap”, 8th International Conference on Dense Z-pinches, Biarritz, France, Jun 2011.

11. M.E. Weller, A. S. Safronova, V. L. Kantsyrev, A. A. Esaulov, A. Stafford, K. M.

Williamson, I. Shrestha, G. C. Osborne, V. Shlyaptseva, S. Keim, S. B. Hansen, “Analysis of Radiation from Uniform and Combined Ag Planar Wire Arrays “, 38th International Conference on Plasma Science, Chicago, IL, Jun 2011.

2011 Poster Presentations (20) 1. A.A. Anderson, V. V. Ivanov, P. Hakel, R. C. Mancini, J. P. Chittenden, A. P. Shevelko, P.

Wiewior, S. D. Altemara, D. Papp, T. Durmaz, N. Niasse, “Study of Wire-Array Z-Pinches with Absorption Spectroscopy and UV Diagnostics”, Stewardship Science Academic Alliances, Washington DC, Feb 2011.

2. J.Iratcabal, B. Bach, T. Darling, Z. McCormick, E. McKee, P. Neill, J. Thompson,

P. Wiewior and A. Covington, “Development of a Multi-Parameter Event-Mode Apparatus for the Study of Laser Produced Plasmas”, International Workshop on Radiation from High Energy Density Plasmas (RHEDP), Reno, NV, Mar 2011.

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3. S.F. Keim, M.E. Weller, V.L. Kantsyrev, A.S. Safronova, A.A. Esaulov, I. Shrestha, G.C. Osborne,V. V.V. Shlyaptseva, “ Analysis of Ablation Dynamics and Radiative Properties of Ag Single Wire Z-pinches on Zebra at UNR”, 53rd Annual Meeting of the Division of Plasma Physics, Salt Lake City, UT, Nov 2011.

4. G.C. Osborne, V.L. Kantsyrev, A.S. Safronova, A.A. Esaulov, U.I. Safronova, I. Shrestha,

V.V. Shlyaptseva, K.M. Williamson, M.E Weller, “Radiative Properties and Implosion Characteristics of Planar Tungsten Wire Arrays on the Zebra Generator”, International Workshop on Radiation from High Energy Density Plasmas (RHEDP) , Reno, NV, Mar 2011.

5. G.C. Osborne, V.L. Kantsyrev, A.A. Esaulov, A.S. Safronova, M.E. Weller, K.M.

Williamson, I. Shrestha, V.V. Shlyaptseva, “Implosion Characteristics of Tungsten and Gold Single Planar Wire Arrays on UNR Zebra Generator”, 8th International Conference on Dense Z-pinches, Biarritz, France, Jun 2011.

6. R.Pandit, Y. Sentoku, “Effects of radiation damping in extreme ultra-intense laser-plasma

interaction”, 53rd Annual Meeting of the American Physical Society Division of Plasma Physics, Saltlake City, UT, Nov 2011.

7. Y.Paudel, A.S. Safronova, V.L. Kantsyrev, A.Y. Faenov, M.E. Weller, I. Shrestha, V.

Shlyaptseva, G.C. Osborne, J. Croteau, A. Merwin, S. Feldman, K. Serratto, A. Bernstein, T. Ditmire, J. Frenje, R. Petrasso, N. Renard-Le Galloudec, “Protons/Ions Beam Characteristics from Short Pulse Laser Interactions with Thin Foil Targets and Their Correlation with Coherent Transition of Radiation”, International Workshop on Radiation from High Energy Density Plasmas (RHEDP) , Reno, NV, Mar 2011.

8. A.S. Safronova, A. Stafford, M.E. Weller, P.G. Cox, S.F. Keim, A.A. Esaulov, U.I.

Safronova, S. F. Keim, V.L. Kantsyrev, I. Shrestha, K.M. Williamson, G.C. Osborne, V. Shlyaptseva, P. Wiewior, N. Renard-LeGalloudec, Y. Paudel, N.D. Ouart, A.Ya. Faenov, W.R. Johnson, “ Progress on Theoretical X-ray/EUV Spectroscopy and Imaging Studies of Wire Array and Laser-produced Plasmas and Applications to Astrophysics”, NNSA / 2011 Stewardship Science Academic Alliances Symposium, Washington D.C., Feb 2011.

9. Y.Sentoku, R. Pandit, “Effects of radiation damping in ultra-intense laser matter interaction

at extreme intensity regime”, 53rd Annual Meeting of the American Physical Society Division of Plasma Physics, Saltlake City, UT, Nov 2011.

10. V.V. Shlyaptseva, V.L. Kantsyrev, A.S. Safronova, A.A. Esaulov, I. Shrestha, K.M.

Williamson, G.C. Osborne, M.E. Weller, A. Stafford, S. Keim, “Studying wire array and X-pinch plasmas from Alumel wire loads”, 8th International Conference on Dense Z-pinches, Biarritz, France, Jun 2011.

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11. I.Shrestha, V.L. Kantsyrev, A.S. Safronova, A.A. Esaulov, K.M. Williamson, G.C. Osborne, V.V. Shlyaptseva, "Progress on study of hard x-ray and electron beam generation in Z- and X-pinch plasmas at University-scale generators", NNSA / 2011 Stewardship Science Academic Alliances Symposium, Washington D.C., February 15-17, 2011.

12. I.Shrestha, V.L. Kantsyrev, A.S. Safronova, A.A. Esaulov, K.M. Williamson, G.C. Osborne,

M.E. Weller, V.V. Shlyaptseva, A. Stafford, “Study of Electron Beams in Z-pinch Plasmas Through Polarization of Lines and Continuum Radiation”, International Workshop on Radiation from High Energy Density Plasmas (RHEDP) , Reno, NV, March 15-18, 2011.

13. V.I. Sotnikov, B. Himed, I. Paraschiv, E.S. Yasin,C. Ng, B. Oliver,T.A. Mehlhorn,

“Scattering of high-frequency electromagnetic waves in the presence of interchange instability in a finite-beta plasma”, American Geophysical Union, Fall Meeting 2011.

14. A.Stafford, A.S. Safronova, U.I. Safronova, V.L. Kantsyrev, A.Y. Faenov, P. Wiewior, N.

Renard-Le Galloudec, I. Shrestha, M.E. Weller, G.C. Osborne, V. Shlyaptseva, Y. Paudel, “Analysis of New Mg Spectral Features Produced on the Leopard Laser at UNR”, International Workshop on Radiation from High Energy Density Plasmas (RHEDP) , Reno, NV, March 15-18, 2011.

15. A.Stafford, A. S. Safronova, V. L. Kantsyrev, A. A. Esaulov, M. E. Weller, K. M.

Williamson, G. C. Osborne, I. Shrestha, V. Shlyaptseva, C. A. Coverdale, N. D. Ouart, S. C. Bott, “Analysis of New Mid-Atomic Number Precursor Wire Array Experiments on the 1-MA Pulsed Power Generator at UNR”, 38th International Conference on Plasma Science, Chicago, IL, June 26-30, 2011.

16. M.E. Weller, A.S. Safronova, V.L. Kantsyrev, A.A. Esaulov, A. Stafford, I. Shrestha,

K.M.Williamson, G.C. Osborne, V. Shlyaptseva, S. Keim, P. Wiewior, N. Renard-Le Galloudec,Y. Paudel, N.D. Ouart, A.Ya. Faenov, "Radiation from implosions of mid-atomic-number wire arrays and first comparison with Leopard laser produced data at UNR", NNSA / 2011 Stewardship Science Academic Alliances Symposium, Washington D.C., February 15-17, 2011.

17. P.Wilcox, A. Stafford, U.I. Safronova, A.S. Safronova, V.L. Kantsyrev, A.Y. Faenov, P.

Wiewior, N. Renard-Le Galloudec, I. Shrestha, M.E. Weller, G.C. Osborne, V. Shlyaptseva, Y. Paudel, “Analysis of New Fluorine Spectral Features Including from Hollow Ions Produced on the Leopard Laser at UNR”, International Workshop on Radiation from High Energy Density Plasmas (RHEDP), Reno, NV, March 15-18, 2011.

18. K.M. Williamson, V.L. Kantsyrev,A.A. Esaulov, A.S. Safronova, I. Shrestha, G.C. Osborne,

M.E. Weller, P.G. Cox, V.V. Shlyaptseva, "Impact of load geometry and ablation on implosion dynamics in planar and nested wire arrays", NNSA / 2011 Stewardship Science Academic Alliances Symposium, Washington D.C., February 15-17, 2011.

19. K.M. Williamson, V. L. Kantsyrev, A. A. Esaulov, A. S. Safronova, I. Shrestha, G. C. Osborne, M. E. Weller, V. Shlyaptseva, “Impact Of Load Geometry And Ablation On Radiation Dynamics in Planar And Nested Wire Arrays”, International Workshop on Radiation from High Energy Density Plasmas (RHEDP) , Reno, NV, March 15-18, 2011.

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20. H.A. Zunino, M.E. Weller, A. Stafford, A.S. Safronova, V.L. Kantsyrev, A.S. Chuvatin, I.

Shrestha, G.C. Osborne, I. Shrestha, V. V. Shlyaptseva, S. Keim, “Spectroscopic Analysis of First Experiments of Al Planar Foils and Single Planar Wire Arrays on Zebra at UNR”, 53rd Annual Meeting of the Division of Plasma Physics, Salt Lake City, UT, November 14-16, 2011.

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Staffing

101

A Covington Research Assistant Professor Y Sentoku ProfessorT Darling Research Professor I Paraschiv Research Assistant ProfessorV Ivanov Research Associate ProfessorD Papp Letter of Appointment P Leblanc Graduate StudentR Presura Research Associate Professor R Pandit Graduate StudentP Wiewior Research Assistant Professor R Royle Graduate Student

A Anderson Graduate StudentK Chartkunchand Graduate StudentB Hammel Graduate StudentS Haque Graduate StudentZ Johnson Graduate StudentW Largent Graduate StudentE McKee Graduate StudentZ McCormick Graduate StudentM Wallace Graduate Student

A Arias Undergraduate StudentB Talbot Undergraduate Student

Laser Development / Operations

A Astanovitskiy Manager, Mechanical Engineering P Wiewior Research Assistant ProfessorV Nalajala Manager, Electrical Engineering O Chalyy Developmental Technician IV

O Dmitrieva Developmental Technician II D Macaulay Developmental Technician II

L Hennessey Undergraduate StudentR Obenauf Undergraduate StudentD Shedd Undergraduate Student

A Covington Director, ActingV Davis Senior Manager, Scientific Operations G Ferguson (State Funded) Manager, Finance & AdministrationP Schmidt Administrative Assistant IIIM Bajwa Administrative Assistant II

Scientific Staff

Operation & Engineering

Administration & Finance

Theory & SimulationExperimental

Engineering / Operations

102


Operational Statistics

103

Nevada Terawatt Facility College of Science University of Nevada, Reno

104


105


106


107

UNR Physics Department Degrees Granted Sept 1969-Aug 2013 Degrees Granted

Year M.S. Ph.D. Total Grad.

B.S.

-8/69 57 6 63 9/69-8/79 40 26 66 9/79-8/89 28 13 41 9/89-8/90 1 2 3 9/90-8/91 7 3 10 9/91-8/92 6 3 9 9/92-8/93 6 4 10 9/93-8/94 3 2 5 9/94-8/95 3 2 5 9/95-8/96 3 2 5 9/96-8/97 3 1 4 9/97-8/98 2 3 5 9/98-8/99 2 4 6 9/99-8/00 1 2 3 9/00-8/01 2 2 4 9/01-8/02 1 2 3 9/02-8/03 3 6 9 9/03-8/04 4 6 10 9/04-8/05 2 2 4 3 9/05-8/06 11 4 15 5 9/06-8/07 2 5 7 6 9/07-8/08 8 5 13 5 9/08-8/09 1 6 7 3 9/09-8/10 2 6 8 9 9/10-8/11 2 13 15 6 9/11-8/12 4 6 10 14 9/12-8/13 1 6 7 Total 205 142 347 48 Total Advanced Degrees Sept 1999 – Aug 2013

44 71 115

Compiled by A.M.C. 23 Jan 2013 (needs verification)

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MS Totals by area since AY 1999/2000

Academic Year AMO HEDP ATMS CM ChemP Misc Total 9/99-8/00 1 0 0 0 0 1 9/00-8/01 1 0 0 1 0 2 9/01-8/02 1 0 0 0 0 1 9/02-8/03 0 1 2 0 0 3 9/03-8/04 1 0 3 0 0 4 9/04-8/05 0 1 6 1 0 2 9/05-8/06 2 3 5 1 0 11 9/06-8/07 2 0 0 0 0 2 9/07-8/08 0 4 3 1 0 8 9/08-8/09 0 1 0 0 0 1 9/09-8/10 1 1 0 0 0 2 9/10-8/11 1 1 0 0 0 2 9/11-8/12 2 1 1 0 0 4 9/12-8/13 0 1 0 0 0 1 9/13- Total: 11 12 20 4 4 50

PhD Totals by area since AY 1999/2000

Academic Year AMO HEDP ATMS ConMat ChemPhys Astro Total 9/99-8/00 2 2 9/00-8/01 2 2 9/01-8/02 1 1 2 9/02-8/03 1 1 4 6 9/03-8/04 3 3 6 9/04-8/05 1 1 2 9/05-8/06 3 1 4 9/06-8/07 3 1 1 5 9/07-8/08 1 1 2 1 5 9/08-8/09 2 2 1 1 6 9/09-8/10 1 4 1 6 9/10-8/11 2 9 2 13 9/11-8/12 1 3 1 1 6 9/12-8/13 3 3 6 9/13- 3 3 Total: 20 33 15 3 2 1 74

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Nevada Terawatt Facility Annual Report

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