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SLAC NATIONAL ACCELERATOR LABORATORYACCELERATOR RESEARCH DIVISION

January, 2011

FY2011-Q1 Quarterly Report (Oct-Dec, 2010)

Table of Contents:

1. ARD Administration 2

2. Advanced Accelerator Research Department 3 AARD – Microwave 3 AARD – Plasma 5 AARD – Laser 5 AARD – Feedback & Dynamics 6

3. Beam Physics Department 7 Collective Effects 7 FEL Physics 9 Advanced Computation 10 Beam Optics & Non-Linear Dynamics 11

4. Accelerator Design Department 11 ILC 12 FNAL Project-X 13 X-Band 14 LARP 15 SuperB 16

5. Accelerator Physics & Engineering Department 16 ATF2 16 CTF3 16 FACET 17 LCLS 17 LCLS-II 18 LHC 18

6. Test Facilities Department 18 ASTA 19 NLCTA 19 FACET User Area 20 End Station A 20 End Station B 20 ECHO Experiments 20

7. FACET Construction 21

A U.S. Department of Energy Research Facility Operated Under Contract by Stanford University

Accelerator Research Division Quarterly Report – 2011/Q1

1. ARD Administration

The Accelerator Research Division (ARD) is a division within SLAC’s Accelerator Directorate. The division is supported with an annual budget of roughly 40 M$ from the US Department of Energy, Offices of Basic Energy Science and High Energy Physics. It consists of roughly 110 physicists, engineers and technicians, including 5 Stanford faculty members, and is divided into five departments:

Advanced Accelerator Research Beam Physics Accelerator Design Accelerator Physics and Engineering Test Facilities

ARD’s mission is to develop accelerator science and technology that will enable new accelerators in photon science and high energy physics as well as other fields of science, medicine and industry with R&D aimed at near-term, mid-term, and long-term development. It has a world renowned research program in advanced acceleration techniques and is engaged in R&D on some of the most advanced accelerators in the world including the Large Hadron Collider at CERN and the Linac Coherent Light Source at SLAC. The division operates three test facilities dedicated to accelerator research: the Accelerator Structure Test Area, the NLC Test Accelerator and the FACET facility.

This report is intended to highlight ARD’s research program and describe progress and advances made in the previous fiscal quarter. Its intended audience is the Directorate and Laboratory management. In addition it is will help ARD staff understand the breadth and strength of the division research program and work that their colleagues are engaged in.

General and more specific information about ARD can be found in: slacportal.slac.stanford.edu/sites/ard_public/Pages/Default.aspx and the ARD organization chart is shown in: slacportal.slac.stanford.edu/sites/ard_public/SiteCollectionDocuments/ARDOrgChart-feb-2011-v2.pdf.

The first quarter of FY11 was a very busy time. In late September, the LCLS-II baseline was changed from an expansion using the existing tunnel to a two-tunnel option. The two-tunnel option has greater expansion capability. DOE endorsed this decision which was great news but then wanted a CDR by March/April of 2011! Next, there was a one-day workshop organized by the DOE BES on Test Facilities for Accelerator R&D and utilization of the user facilities such as SPEAR and LCLS for accelerator R&D. This was then followed by a meeting of the OHEP advisory committee P5 to consider additional operation of the Tevatron at Fermilab – it recommended, yes, provided additional operation funds could be found. Then the CLIC/ILC workshop was held at CERN and then the SLAC AED review was held at SLAC. That was October!

In November, Norbert Holtkamp joined the lab and started helping ARD develop a more focused, well supported program. The primary challenge ahead is determining the direction of the linear collider program and the future of the normal conducting rf R&D while strengthening the FEL R&D program to enable SLAC to remain a leader in the field of x-ray FEL’s.

Norbert has set up a blog: https://slacspace.slac.stanford.edu/sites/ad/blog/default.aspx, an email inbox:https://slacportal.slac.stanford.edu/sites/ad_public/suggestion/Pages/default.aspx and has an open door policy for anybody with ideas on how to improve the accelerator operations or research programs at SLAC.

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https://portal.slac.stanford.edu/sites/ad_public/suggestion/Pages/default.aspx

https://slacspace.slac.stanford.edu/sites/ad/blog/default.aspx

https://portal.slac.stanford.edu/sites/ard_public/SiteCollectionDocuments/ARDOrgChart-feb-2011-v2.pdf

https://portal.slac.stanford.edu/sites/ard_public/SiteCollectionDocuments/ARDOrgChart-feb-2011-v2.pdf

https://portal.slac.stanford.edu/sites/ard_public/Pages/Default.aspx


During the Fall of the academic year 2010-2011 one accelerator physics course was taught by Prof. Ron Ruth entitled Introduction to Accelerator Physics (APP-324). This course is a broad introduction to accelerator and beam physics and this year included a laboratory at SPEAR III near the end of the course. The enrollment was very successful and included 9 registered students and several other regular auditors. The laboratory was especially popular and the performance by the students was outstanding. This spring the education committee will meet to discuss graduate student supervision policy and courses for next year.

Finally, ARD is organizing Invited Accelerator Seminars again for the SLAC community: https://slacportal.slac.stanford.edu/sites/ard_public/ardhq/seminars/Pages/default.aspx. The first two talks in January will be by Michael Borland and then Claudio Pellegrini. Please send suggestions for future seminars to Mike Litos: [email protected].

2. Advanced Accelerator Research Department

The Advanced Accelerator Research Department (AARD) is dedicated to basic and applied research in accelerator science with the goals of advancing the state-of-the-art and educating accelerator scientists. Our investigations lie at the forefront of accelerator physics, and incorporate a wide variety of fields ranging from microwave engineering, plasma physics, electromagnetic theory, and ultra-fast lasers to physical optics, materials science, formal control theory, ultrafast electronics, and nanofabrication engineering and design. AARD efforts focus on understanding and extending the limits of accelerator technology to expand capabilities in energy, luminosity, beam power, and timescale to extend the reach of discovery science. Primarily developed for High Energy Physics and Basic Energy Science, these accelerator technologies will also benefit medicine, food safety, biology, and homeland security.

The department consists of four groups focusing on the four main research directions:

Microwave : Development of normal conducting accelerators and power sources, with a focus on understanding the limitations in high-gradient and high-frequency microwave structures.

Plasma: Use of short, intense pulses of electrons and positrons to create waves in a plasma (ionized gas) capable of producing orders of magnitude higher accelerating gradients than traditional accelerators

Laser: Investigation of techniques for accelerating electrons and positrons using lasers and dielectric microstructures, with acceleration gradients orders of magnitude larger than traditional accelerators

Feedback & Dynamics: Development of novel ultrafast and wide-bandwidth electronic circuits, signal processing systems, and laboratory measurement techniques for particle accelerators

AARD—Microwave

High Gradient Research:

Structure Manufacturing Technology (Collaborative work with CERN & KEK)o Coordinated the work for two TD24_VG1.8 structures. They are under construction.

After the completion, one with SLAC flanges will be tested at the NLCTA and one with KEK flanges will be shipped to Japan.

o Organized and performed the chemical etching studies on the parts for high gradient accelerator structures. Historical records for the structures in past years and SEM,

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mailto:[email protected]

https://portal.slac.stanford.edu/sites/ard_public/ardhq/seminars/Pages/default.aspx


microscopic pictures taken before and after various etching times were analyzed in order to make decision for the processing of future structures.

o Participated design and fabrication for three short deflectors: calculated all RF parameters for T11 and T27 structures; submitted the job and worked on various fabrication related issues.

o Worked to produce a T105 accelerator structure: collected available and usable parts; arranged and monitored the QC procedures; prepared the work for coupler electrical design and mechanical design integration.

Novel Structure Designs o Designed structure for test of optimized shaped cavity (three cells – optimized cavity cell

and two coupling cells)o Completed design study of accelerator cavity geometry to be used in parallel-fed standing

wave accelerator structureo Generated concept for planar (2D) construction of parallel-fed standing wave accelerator

structureo Cryogenic system to test normal-conducting accelerating structures at cryo-temperatures.o Developed Structure made of stainless-steel plated with Cu.

High-Gradient Experimentso Tested Hard-CuCr high-shunt-impedance 1C-SW-A3.75-T2.6-Clamped-CuCr-SLAC-#1.o Tested Dual-feed-side-coupled high-shunt-impedance 1C-SW-A3.75-T2.6-2WR90-Cu-

SLAC-#2.o Tested Hard-copper highest-shunt-impedance 1C-SW-A2.65-T2.0-Clamped-Cu-SLAC-

#1.o Manufactured two accelerator structures for advanced in-situ diagnostics, Single-cell-sw-

structure with viewport 1C-SW-A3.75-T2.6-Ch-ViewPort-Cu.o Manufactured New pulse-heating cavity with viewports for in situ diagnosticso Tested CERN Power-Extraction and Transfer structure PETS2.o Tested 10 Cell Traveling wave structure C10-VG0.7.5

Manufactured and delivered to collaborators:o Hard-copper-cells for advanced coating to Yale.o Mode launchers for Argonne National Lab.

RF Undulatorso Written a new set of Codes capable of optimizing the RF structure through generic

algorithmso Designed the first RF undulator and cold tested a section to verify the results of the

optimized designo Design novel Devices which is capable of producing K=1 at 1.35 cm undulator

wavelength with a reasonable RF power levels. Superconducting Material Research

o Tested New stratified Media based on MgB2o Tested Single crystal Nbo Designed a new structure cavity for testing residual resistance.

Publications and Talks

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o Invited Talk at ECLOUD 10 workshop “Control of Transverse Intra-Bunch Instabilities using GHz Bandwidth Feedback Techniques” - Claudio Rivetta et al

o “RF system models for the CERN Large Hadron Collider with application to longitudinal dynamics”. T. Mastorides, C. Rivetta, J.D. Fox, D.Van Winkle, (SLAC), P. Baudrenghien, (CERN). Oct. 1, 2010. (Published Oct. 1, 2010). 11pp. Published in Phys.Rev.ST Accel.Beams 13:102801, 2010.

o Multiple talks at the November 2010 LARP collaboration meeting, LLRF results presented by CERN at the Evian LHC meeting.

AARD – Plasma

FACET

o Completed internal review of FACET proposals in advance of SAREC review (with other TFD, S20, ARD staff)

o Developed solution to simultaneously deliver full beam rate in S0-19 for linac feedback systems with reduced rate to FACET S20 IP – necessary for PWFA and all experiments using notch collimator.

o Worked with RP to develop shielding solution for notch collimator area of S20 beamlineo Worked with controls department on ongoing integration of high-performance CMOS

cameras and plasma oven hardware into EPICS DAQ and control systemo Worked with Bill White’s group to identify and layout future experimenter laser room

and system in NW corner of LCLS laser buildingo Improved particle tracking model of S20 beamline to quantify emittance growth due to

chromaticity, ISR and CSR.

Publications and Talkso Two invited talks on PWFA: Super-Strong Fields in Plasmas and SciDAC Compass

AARD – Laser

NLCTA Beam Testso Record emittances <3 pi mm-mr at 25 pC achieved with near-complete emittance

preservation through the dispersive transport lines to the E163 experimento 11x12 micron spot sizes were produced at the fiber test location (5x5 micron needed)o The first PCF fiber test was attempted to look for the Cerenkov wakefield in the fibero A high resolution near-IR spectrometer was assembled with 4 PCF test fibers for beam-

driven wakefield tests A Mach-Zehnder Interferometer was built and used to quantify the phase length dependence on

temperature for commercial PCF fiber (1/)d/dT=6.3 ppm/C, making temperature stabilization requirements for a working PCF accelerator quite modest.

9 (of 17) layer woodpile structures were completed; alignment and bonding methods were explored to join the two halves into a complete structure

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The first lithographic grating accelerator structures were fabricated at CIS Incom successfully produced 1 mm long large-array PCFs with accelerator modes in the

10 micron operating range, and aim to drawn down to features in the 2 micron operating range. Publications:

o C.-K. Ng, R. J. England, L.-Q. Lee, R. Noble, V. Rawat and J. Spencer, "Transmission and Radiation of an Accelerating Mode in a Photonic Bandgap Fiber", PRST-AB, 13, 121301 (December 2010).

o C. Carlsten, E. Colby, et al¸”New source technologies and their impact on future light sources”, NIM A, 622, p.657-669, (2010).

o J. England, et al, “Single-Mode Coupler Development for Photonic Crystal Structures”, in preparation for submission to PRST-AB. (2011)

AARD—Feedback & Dynamics

The central focus of the LARP LLRF effort involved continued validation of the longitudinal noise-driven diffusion models via machine measurements at LHC. The predictions from the LLRF beam simulation and noise model were tested via dedicated LHC machine runs where excess noise was added to the LLRF feedback loops while the bunch length and growth rate were measured. This work established noise thresholds for the accelerating cavity noise spectrum.

High-current estimates of coupled-bunch beam stability were made in preparation for 2011 LHC operations.(T. Mastorides). The simulation model was expanded to incorporate the 1-turn delay (comb loop) feedback, and the configuration tools were expanded in anticipation of comb loop commissioning in early 2011 LHC. (C. Rivetta) The work include two trips by Themis, 1 trip by Claudio to CERN.

The LARP ECLOUD wideband vertical feedback project focused on continued analysis of the MDdata taken last summer

o Using a motion RMS analysis technique (M. Swiatlowski)o Using comparisons with WARP nonlinear simulations (R. Secondo, LBL, C. Rivetta).o Work on techniques to estimate system dynamics via reduced models continues (O.

Turgut, C. Rivetta).

Model and simulation of hardware limitations (real feedback model) to be included in WARP/CMAD simulation code (C. Rivetta, M. Pivi).

The hardware effort prototyped a 4 GS/sec synchronized excitation system which will be used at the SPS in future dynamics measurements. 5 100W 1 GHz amplifiers for use at the SPS were specified and ordered as part of the experimental project. The joint SLAC/LBL kicker evaluation started to produce a design report in mid 2011 (J. Fox, J. Olsen).

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LARP PS2 report, Modeling of RF station impedance and low-order mode longitudinal beam dynamics, stability estimates (C. Rivetta)

J. Fox and C. Rivetta discussed possible RF noise and longitudinal motion studies with SSRL staff.

J. Fox taught his “Energy choices for the 21st Century” Applied Physics course.

Staffing - T. Mastorides awarded a Toohig Fellowship. M. Swiatlowski rotated with the group as a Stanford Physics department RA in the fall, we are still recruiting a Ph.D. graduate student for the group.


o Invited Talk at ECLOUD 10 workshop “Control of Transverse Intra-Bunch Instabilities using GHz Bandwidth Feedback Techniques” - Claudio Rivetta et al.

o “RF system models for the CERN Large Hadron Collider with application to longitudinal dynamics”. T. Mastorides, C. Rivetta, J.D. Fox, D. Van Winkle, (SLAC), P. Baudrenghien, (CERN). Oct. 1, 2010. (Published Oct. 1, 2010). 11pp. Published in Phys.Rev.ST Accel.Beams 13:102801, 2010.

o Multiple talks at the November 2010 LARP collaboration meeting, LLRF results presented by CERN at the Evian LHC meeting.

3. Beam Physics Department

The mission of the Beam Physics Department (BPD) is primarily focused on beam theory. There are three beam dynamics groups: Collective Effects, FEL Physics, and Beam Optics & Nonlinear Dynamics. These groups supports the operating accelerators at SLAC and studies beam physics that can enable or limit future accelerators and its members work closely with other ARD groups and programs. BPD also contains the Advanced Computation Group. This group develops massively parallel computing techniques to solve problems in beam physics. It supports accelerator programs at SLAC as well as across the US. The R&D enables improved understanding of accelerator phenomena through simulation and allows a cost-effective accelerator design process through extensive calculation.

Collective Effects:

Electron cloud simulations for the ILC damping ring and CESRTA. SPEAR3 optics and beam ion instability study. Electron cloud simulations for the ILC damping ring and CESRTA. Study of short bunch/pulse measurement in LCLS. Study of CSR impedance in short magnets and undulators. High-frequency impedance of small-angle tapers and collimators. Simulations of threshold of the microwave instability in electron storage rings. Talks and papers published or submitted (see also papers 1and 2 in the FEL Physics):

o L. Wang and M. Pivi. Talk at ECLOUD10 “TRAPPING OF ELECTRON CLOUD IN ILC/CESRTA QUADRUPOLE AND SEXTUPOLE MAGNETS”. Abstract “The Cornell Electron Storage Ring (CESR) has been reconfigured as an ultra low emittance damping ring for use as a test accelerator (CesrTA) for International

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Linear Collider (ILC) damping ring R&D. One of the primary goals of the CesrTA program is to investigate the interaction of the electron cloud with low emittance positron beam to explore methods to suppress the electron cloud, develop suitable advanced instrumentation required for these experimental studies and benchmark predictions by simulation codes. This paper reports the simulation of the electron-cloud formation in CESRTA and ILC quadrupole and sextupole magnets using the 3D code CLOUDLAND. We found that electrons can be trapped with a long lifetime in a quadrupole and sextupole magnet due to the mirror field trapping mechanism. We study the effects of magnet strength, bunch current, ante-chamber effect, bunch spacing effect and secondary emission yield (SEY) in great detail”.

o R. Warnock. Keynote talk "Coherent Synchrotron Radiation in Whispering Gallery Modes: Theory and Evidence". Workshop "Topics in Coherent Synchrotron Radiation: Experimental Consequences of Radiation Impedance", Canadian Light Source, Saskatoon, Saskatchewan, Nov. 1-2, 2010.

o G. Stupakov and D. Zhou. “Longitudinal impedance due to coherent undulator radiation in a rectangular waveguide”, SLAC-PUB-14332. Abstract: “In this paper we investigate the longitudinal impedance due to coherent undulator radiation in a rectangular waveguide. We find that the impedance exhibits narrow peaks at resonant frequencies at which waveguide modes are in synchronism with particle motion in the undulator. Analytical calculations are compared with numerical simulations carried out with a computer code that solves parabolic equation for the electromagnetic field”.

o G. Stupakov and B. Podobedov. "High-frequency impedance of small-angle tapers and collimators". Phys. Rev. ST Accel. Beams 13, 104401 (2010). Abstract: “Collimators and transitions in accelerator vacuum chambers often include small-angle tapering to lower the wakefields generated by the beam. While the low-frequency impedance is well described by Yokoya’s formula (for axisymmetric geometry), much less is known about the behavior of the impedance in the high-frequency limit. In this paper we develop an analytical approach to the high-frequency regime for round collimators and tapers. Our analytical results are compared with computer simulations using the code ECHO”

o K. L. F. Bane, Y. Cai, and G. Stupakov, “Threshold studies of the microwave instability in electron storage rings”, Phys. Rev. ST Accel. Beams 13, 104402 (2010). Abstract: “We use a Vlasov-Fokker-Planck program and a linearized Vlasov solver to study the microwave instability threshold of impedance models: (1) a Q=1 resonator and (2) shielded coherent synchrotron radiation (CSR), and find the results of the two programs agree well. For shielded CSR we show that only two dimensionless parameters, the shielding parameter and the strength parameter, are needed to describe the system. We further show that there is a strong instability associated with CSR. We, in addition, find another. We find that the threshold to this instability depends strongly on damping time, and that the tune spread at threshold is small—both hallmarks of a weak instability”.

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o Daniel F. Ratner and Alexander W. Chao “Steady-State Microbunching in a Storage Ring for Generating Coherent Radiation” Phys. Rev. Lett. 105, 154801 (2010) Abstract: “Synchrotrons and storage rings deliver radiation across the electromagnetic spectrum at high repetition rates, and free electron lasers produce radiation pulses with high peak brightness. However, at present few light sources can generate both high repetition rates and high brightness outside the optical range. We propose to create steady-state microbunching (SSMB) in a storage ring to produce coherent radiation at a high repetition rate or in continuous wave mode. In this Letter we describe a general mechanism for producing SSMB and give sample parameters for extreme ultraviolet lithography and submillimeter sources. We also describe a similar arrangement to produce two pulses with variable spacing for pump-probe experiments. With technological advances, SSMB could reach the soft x-ray range (< 10 nm).

FEL Physics:

LCLS-II design: optimal undulator configuration, self-seeding and polarization control studies, start-to-end simulations, CDR production.

General LCLS machine studies and user operation support. Ultrashort temporal diagnostics: developed and tested a longitudinal transformation method to

measure ultrashort (~1 fs) electron bunches; statistical analysis of the LCLS FEL properties to study its temporal duration and transverse coherence.

FEL theory: develop a Hamiltonian formalism for FEL equations, use an adiabatic approximation to study FEL gain when the transverse beam size varies in the undulator.

FEL scheme: study a novel approach to introduce nm-level density modulation on the electron bunch before it enters the undulator.

Stanford AP class: Introduction to Accelerator Physics, lectures and lab courses. Paper published or submitted:

o “Analysis of shot noise in electron beams” D. Ratner, Z. Huang, G. Stupakov, submitted to PRSTAB. Abstract “Shot noise can affect the performance of free electron lasers (FELs) by driving instabilities (e.g.the microbunching instability) or by competing with seeded density modulations. Recent papers have proposed suppressing shot noise to enhance FEL performance. In this paper we calculate the noise amplification from an energy modulation (e.g. electron interactions from space charge or undulator radiation) followed by a dispersive section. We show that for a broad class of interactions, selecting the correct dispersive strength suppresses shot noise across a wide range of frequencies. The final noise level depends on the beam's energy spread and the properties of the interaction potential. We confirm and illustrate our analytical results with 1-D simulations”.

o “Two-chicane compressed harmonic generation of soft x-rays” D. Ratner, A. Chao, Z. Huang, submitted to PRSTAB: Abstract “Seeding an electron bunch prior to compression simultaneously shifts the laser modulation to shorter wavelengths while decreasing the required modulation amplitude. The final x-ray wavelength is then tunable by controlling the compression factor with the RF phase. In this paper we describe a two chicane scheme that allows for large modulation amplitudes, extending the method to photocathode beams with significant uncorrelated energy spreads. The downside of such compressed seeding is the need to maintain bunching across an extended accelerator region. We present analytical

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estimates and computer simulations to study tolerances for a sample lattice. We also note that transportation of fine compressed modulation structure is helped by error self-correction in the second chicane, an effect that may be of more general interest.”

o 3. “Generation of coherent x-ray radiation through modulation compression” Ji Qiang (LBL), J. Wu, posted at arXiv:1012.5446v1 Abstract “In this letter, we propose a scheme to generate tunable coherent X-ray radiation for future light source applications. This scheme uses an energy chirped electron beam, a laser modulators, a laser chirper and two bunch compressors to generate a prebunched kilo-Ampere current electron beam from a few tens Ampere electron beam out of a linac. The initial modulation energy wavelength can be compressed by a factor of 1 + hbRa

56 in phase space, where hb is the energy bunch length chirp introduced by the laser chirper, Ra

56 is the momentum compaction factor of the first bunch compressor. As an illustration, we present an example to generate more than 400 MW, 170 atto-seconds pulse, 1 nm coherent X-ray radiation using a 60 Ampere electron beam out of the linac and 200 nm laser seed. Both the final wavelength and the radiation pulse length in the proposed scheme are tunable by adjusting the compression factor and the laser parameters.”

Advanced Computation Group

Simulation of wakefield coupling in the CLIC two-beam module. T3P is used to determine the transverse wakefield coupling between the PETS (Power Extraction and Transfer Structure) for the drive beam and the accelerating structures for the main beam in CLIC. The figure shows the first-ever results for such calculations for a simplified coupled mesh model of the PETS and two TD24 accelerating structures. The simulation is initiated with a single drive beam at an offset in the PETS to excite the transverse wakefields that couple to the TD24 structures. The evolution of the transverse electric field magnitude along the axis of the TD24 as a function of time is shown in the insert at the bottom left figure.

Design of Project-X Main Injector cavity. Omega3P has been used to obtain a preliminary design of the Project-X Main Injector cavity. The design satisfies the tuning range requirements through the use of a ferrite core. Damping of the longitudinal and transverse higher-order-modes (HOM) using a loop HOM coupler has been evaluated. A 7-element Chebyshev high-pass filter located in the HOM coax has been used to cut off the coupling of the fundamental mode. Further optimization will be carried out to improve the cavity power coupling and damping efficiency.

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http://lanl.arxiv.org/abs/1012.5446v1


Development of Multi-physics Module in ACE3P. A thermal and a mechanical solver have been implemented in the multi-physics module TEM3P within ACE3P and successfully benchmarked with ANSYS. Particularly important for superconducting cavities, the nonlinear thermal boundary conditions and thin layer modeling have been verified for the modeling of cold-warm transition in the power coupler. TEM3P has the advantage of being able to solve large–scale problems which is of great interest to facilities such as JLab and FNAL for their superconducting cavity studies.


o C.-K. Ng, R. J. England, L.-Q. Lee, R. Noble, V. Rawat, and J. Spencer, “Transmission and radiation of an accelerating mode in a photonic band-gap fiber”, Phys. Rev. ST Accel. Beams 13, 121301 (2010).

Beam Optics & Non-Linear Dynamics


o A paper, based on an invited talk at the 8th International Conference in Charged Particle Optics, 12-16 July 2010, Singapore, was accepted for publication in Nucl. Instrum. Methods Phys. Res., Sect. A. Yunhai Cai, “Single-Particle Dynamics in Electron Storage Rings with Extremely Low Emittance”, SLAC-PUB-14321, November, 2010. Abstract: Electron storage rings are widely used for high luminosity colliders, damping rings in high-energy linear colliders, and synchrotron light sources. They have become essential facilities to study high-energy physics and material and medical sciences. To further increase the luminosity of colliders or the brightness of synchrotron light sources, the beam emittance is being continually pushed downward, recently to the nanometer region. In the next decade, another order of reduction is expected. This requirement of ultra-low emittance presents many design challenges in beam dynamics, including better analysis of maps and improvement of dynamic apertures. To meet these challenges, we have refined transfer maps of common elements in storage rings and developed a new method to compute the resonance driving terms as they are built up along a beamline. The method is successfully applied to a design of PEP-X as a future light source with 100-pm emittance. As a result, we discovered many unexpected cancelations of the fourth-order resonance terms driven by sextupoles within an achromat.

4. Accelerator Design Department

The Accelerator Design Department (ADD) is focused on the design of normal conducting and superconducting linear colliders and the development of the required technology. In addition, the department investigates applications of these technologies that may enable other facilities such as Project-X as well as other SLAC facilities. This R&D is aimed at a next generation TeV-scale linear collider but may have application to compact light sources, industrial and medical accelerators.

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The major projects within ADD are ILC, FNAL Project-X, X-Band, LARP and Super-B.

ILC: For the ILC RF system, the SLAC effort is focused mainly on developing lower cost and more reliable rf components for the main linacs. Areas of research include:

o Marx Modulator: Have recently been studying lifetime issues for the capacitors in the P1 MARX. It appears their shortened lifetime is related to their discharge level, perhaps due the heating from the recharge current. Tests of the lifetime as a function of the discharge level indicate the P2 Marx should not have this problem. For this purpose, the P1 Marx is running at a shorter pulse length to simulate the P2 operation. At this pulse length, few modulator or klystron faults have been observed with 10 MW rf output power.

o Global RF Distribution: The 10 m long, 0.5 m diameter ‘big pipe’ has been operated resonantly at field levels equivalent to 300 MW travelling wave operation, as would be the case at ILC. A few breakdowns were observed during 100 hours of operation at 5 Hz with 1.2 ms pulses. They appear to be coming from the Coaxial Tapoff that feeds the pipe, and its windows will be upgraded soon to see if this eliminates the problem.

o Local RF Distribution: A second generation, 8-feed, variable power rf distribution system is being built for FNAL’s second cryomodule. This version has remote-controlled phase shifters to adjust the power split among the cavities. The first two feed sub-unit will be tested soon (the basic phase shifter concept has already been demonstrated at high power).

o Couplers: Two more pairs of couplers (Build #7 and #8) were completed and sent to FNAL. Work is progressing slowly on a cold coupler section that is being built by the

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Klystron Department using joining methods other than e-beam welding, which limits the number of vendors who can manufacture them.

o For the ILC Electron Sources, SLAC purchased and installed 2 new Verdi lasers in late FY10. In October, there was a visit to KM Labs in Boulder, CO where their laser was operating at 1.5 MHz at 5 W (3 micro-J/bunches). Received KM Labs SBIR2 ILC prototype laser in December, 2011. This laser is being installed in B006, Room 107. Expect to have laser system running in the second quarter of FY11.

o For the ILC Damping Rings, SLAC is coordinating the international Working Group on the electron cloud R&D ecloud mitigation methods. The Working Group met at Cornell University on October 13, 2010 and gave a preliminary recommendation for the baseline and alternate solutions for the electron cloud mitigation in various regions of the ILC Positron DR. Furthermore, the WG collaborating institutions did extensive simulation work to assess the reduction of new 3.2km DR version bunch spacing to 3ns to double the beam current and luminosity.

o Benchmarking between simulation codes developed at SLAC and CesrTA experimental data are promising. At SLAC, we benchmarked experimental data for the electron cloud build-up in wiggler and quadrupole regions. The single-bunch instability code and the CesrTA data both show a tune shift and the appearance of synchrotron sidebands in the vertical plane in the presence of an electron cloud. Furthermore, an incoherent emittance growth below instability threshold has been observed both in simulations and experimentally. Work is ongoing in FY11 to quantify these effects.

o For the ILC Machine Detector Interface (MDI) in FY11-Q1, eight MDI meetings took place and results were presented at the ILC/CLIC meeting in Geneva in October 2010 and at the SiD Collaboration workshop in November 2010. Details of the weekly meetings are available at http://ilcagenda.linearcollider.org/categoryDisplay.py?categId=188.

o The vibration analysis with supporting measurements at SLAC and CERN are leading to the adoption of a platform design compatible with that preferred by the ILD detector. Work continues on a Frequency Scanning Interferometry (FSI) based alignment system, a re-evaluation of SR backgrounds, and an analysis of HOM induced heating near the IP. A grant request by U. Michigan for FSI work was submitted to SLAC.

FNAL Project X: At the October 2010 PX collaboration meeting at FNAL, a decision was essentially made not to include the 1.3 GHz, 1 GeV accelerator section at the end the 3 GeV CW, SC proton linac as originally planned, but to extend the 650 MHz linac to this energy. We had spent about a year reviewing options for a 30 kW, CW, 1.3 GHz rf source, in particular, solid state amplifiers, which would offer high reliability. Recently, we have started researching 650 MHz CW solid state sources and redoing the SOW with FNAL for this and other PX rf efforts. Currently, we are waiting for funding (400 k$)

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http://ilcagenda.linearcollider.org/categoryDisplay.py?categId=188


from FNAL and a better definition of what we would be responsible for during the R&D phase.

X-Band: The SLAC X-band program includes testing CLIC prototype structures, developing and testing a Dual Mode Cavity to better understand breakdown limitations, developing an X-band gun (with LLNL) and associated test beamline (XTA), upgrading the X-band systems at NLCTA in support of other programs there and developing X-band linac designs for light source applications. Progress is summarized below.

o CLIC: Tested a T18 structure that CERN built using SLAC cleaning and assembly techniques. It performed much better than their earlier structures but not quite as well as the ones assembled at SLAC. Also tested a T24 structure, which is their next iteration design with improved efficiency. It has not performed as well as the T18, although the breakdown rate is decreasing rapidly (as is the case for one being tested at KEK).

o Dual Mode Cavity: A dual-mode cavity was constructed that allows the magnetic and electric surface fields to be varied independently in a coaxial geometry so their relative effects on breakdown can be studied. In the first test, just the TEM mode was powered (from Stn 2) and surface electric fields of 200 MV/m were achieved. It is now setup so the TE mode can be powered as well (from Stn 1) and the surface magnetic field will be varied in time, phase and amplitude to determine its effect for a fixed electric field.

o X-band Gun: The design for an 5.59 cell X-band photocathode gun was completed in collaboration with LLNL for their MEGa-ray project. It is an improvement on one Arnold Vlieks design several years ago and beam transport simulations (using ImpactT and Pic3P) have shown that < 0.5 micron emittances should be achievable for 250 pC bunches with a 200 MV/m cathode field. An X-band gun has an advantage over a S-band gun in that the resulting bunch length is less than half as long, making subsequent bunch compression easier. Construction of the gun will begin shortly and will be LDRD funded.

o XTA: A new beamline in NLCTA (called XTA) is being constructed to test this gun. The beamline includes the gun solenoid, a 1 m X-band accelerator (T105), rf bpms, strip line bpms, an X-band deflecting cavity, profile monitors, quadrupole magnets, a spectrometer bend magnet and Faraday cups. The basic layout for the beamline is complete and parts are being acquired, including control systems originally developed for LCLS. It is expected to be operational later this year.

o NLCTA Upgrades: The Linac Design Group is working with the Test Facilities Group to upgrade the beamline capabilities in the ECHO area at NLCTA. Two deflecting cavities are being added, one for beam heating and one for bunch length and slice energy spread measurements. These will be powered from Stn1 and the Two Pack, respectively, and the rf hardware for this is either being built or recycled from NLC test setups. Also, the spectrometer magnet bend angle is being increased (form 12 to

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30 degrees) to improve resolution. Finally, the Stn 2 rf power is being routed to the XTA area so structure testing can continue and the new X-band gun and accelerator structure can be powered. This work is expected to be completed by the end of April.

o Light Sources: At the XB10 Workshop in Daresbury, we presented studies of a 6 GeV linac based on NLC X-band technology that could deliver LCLS-like bunches for an XFEL. Such a linac is being considered for a 2.6 GeV X-ray FEL facility at KVI in the Netherlands. These linacs use a 250 MeV S-band injector, but from our beam dynamics studies of an X-band gun, and X-band injector is possible as well. For the bunch energy linearization, the T566 component of the bunch compressor chicane can used instead of higher harmonic rf. A complete design for such an all-X-band linac is underway.

o We also consulted with several groups considering the use of X-band, such as PSI, Trieste, NLS and LLNL. More recently, LANL has proposed a 20 GeV X-band linac to produce electron bunches for the MaRIE 50 keV XFEL project. We are currently working on TW structure designs for them that would be optimized for their very low beam loading and long pulse (1500 ns) rf pulse length. This year, we expect to ramp up design work (structure parameters and wakefield suppression) and experiments (long pulse X-band and S-band structure tests) with funding from their LDRD program and from the MaRIE project if they receive CD0 approval as expected this summer.

LARP: In Q1 FY11, we finished the redesign and rebuild of the rotation drives for the jaws. The new design was tested to five times the anticipated torque required for rotation. Testing of the new design in Bldg. 33 required the fabrication of various devices to prevent rotation of the mechanism during the test phase; when assembly is final, welds will keep the parts in place. The device was brought to the Bldg.31 vacuum shop clean room where it resides under N2 environment when not being tested. The 4 bellows were vacuum fired and welded to the base plate and the jaw supports were welded to the other end of the bellows. Leak checking showed 9 scale vacuum. Mechanical work included the rebuild of the RF rotation mechanism on one of the jaws and the final reassembly/rebuild of the drives with W-S2 coated bearings. The UA9 crystal collimation experiment had its annual collaboration meeting at CERN in October 2010 and took its last data run for 2010 in November, both with SLAC participation.

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SuperB: During the past 6 months we developed a correction scheme for the detector solenoidal field. In the first 3 months, we created a compensation scheme for the detector field that included rotating the PM quadrupoles located close to the collision point as well as extra windings and/or modified main coil windings to introduce skew terms in the super-quads in the final focus system of the IR. In addition, the compensation scheme utilizes compensating solenoidal windings to cancel most of the detector field and multiple skew quads and correctors located outside of the detector. Last fall, with the same compensation hardware that was used with the detector field on, an orbit and skew correction scheme was developed to enable the machine to run with the detector field off. With the approval of SuperB in Italy, this group is waiting for direction from DOE on how to proceed.

5. Accelerator Physics & Engineering Department

The mission of the Accelerator Physics & Engineering Department (APE) is to “Make Accelerators Work”. APE works in the gap between what is traditionally considered physics and engineering for the design and operation of existing and near term accelerator facilities. This includes accelerator design and modeling, beam tuning and control, diagnostics, accelerator commissioning and operations. The department core competency is generated by people who combine physics, engineering and accelerator operations expertise.

APE supports a variety of accelerator projects with substantial efforts in:

ATF2: The ATF2 is a test facility designed to demonstrate the linear collider final focus optics using the low emittance beam from the ATF damping ring at KEK in Japan

o The ATF2 non-linear optical system requires the development of new tuning algorithms which are tested on a simulator, then implemented on the accelerator. This quarter beam tuning reduced the final focus spot size to 300nm, limited by the resolution of the Tokyo University interferometer spot size monitor. During the next quarter we expect the spot size monitor to allow the spot sizes to reach 100nm, limited by higher order errors in the magnets.

o The ATF2 uses 37 C-band cavity BPMs with electronics designed by SLAC, cavities constructed by KEK and algorithms and software developed at RHUL. Upgrades this quarter allowed this system to operate at its design resolution of 50nm. During the next quarter we expect to do initial tests of the system with multi-bunch beams and to commission the remaining non-standard BPMs (S-band and IP BPMS).

o This quarter a set of 4 OTRs constructed by IFIC in collaboration with SLAC were commissioned for emittance measurements, reducing the 20 minutes required by the wire scanner based measurement to less than 1 minute.

CTF3: The CTF3 facility at CERN Is designed to demonstrate the high current drive beam required for the CLIC collider

o The CTF3 / CLIC drive beam BPMs present a unique problem: the very high beam currents, designed to generate hundreds of megawatts of RF in extraction structures, must process beam signals at frequencies well below the 12 GHz bunch spacing fundamental frequency, as the beam pipe propagates HOMs at this frequency. In fact it is designed to propagate 130 MW of 12 GHz in its role as RF source for the CLIC accelerator. Until recently the plan was to detect statistical fluctuations in the beam current at 2GHz, away from the X-band main

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beam frequency, but this quarter it was discovered in simulations that this would provide too much sensitivity to beam combiner ring errors. The new design operating at baseband, along with a more conventional main beam BPM design has been submitted to the CLIC CDR.

o The BPM design is expected to be finalized next quarter and plans for future collaboration with SLAC are under consideration.

FACET: FACET is a SLAC project to use the front 2 km of the linac, damping rings and positron system to generate high peak current test beams for plasma wakefield acceleration and other experiments.

o The preparation of the Sector 0-20 systems, damping rings and FACET experimental area is continuing and is completed in time for the scheduled turn-on.

o Last quarter a plan was developed to provide continuous bunch length monitoring for use in feedback at each of the compression stages. Installation of the bunch length monitor hardware and the design of the feedback systems is expected to be completed next quarter.

o Last quarter the possibility of generating THz radiation from the FACET beam was investigated and presented to the SAREC review committee. Hardware to test the THz output will be installed next quarter in preparation for the first FACET run.

LCLS: The SLAC X-ray FEL system, now providing user beams.

o Last quarter the longitudinal feedbacks and physics high level applications were modified to operate with the timeslot control required for 120Hz operation, now available for users. In addition the capabilities of the LCLS physics applications were extended to provide better automation for changing operating conditions and better diagnostics.

o Due to a calculation error, the X-ray beam divergence from the LCLS is 2x larger than originally estimated and overfills the hard X-ray mirrors. Last quarter a plan was developed to install a Be focusing lens in the X-ray diagnostics chamber (“ST0”). The engineering design is complete and parts are expected to be fabricated and installed next quarter for initial testing.

o Last quarter the timing system for the experiments was upgraded to provide better performance and maintainability. This was mostly successful, however one problem that has arisen is that the cavity based beam arrival time monitor developed a problem where the RMS noise increased from 12fs to >30fs (sometimes 100fs). This is being investigated and is expected to be corrected next quarter along with the installation of further upgrades.

o An experiment at SXR demonstrated the use of a GaAs crystal to perform a direct X-ray / Optical cross correlation with <60fs resolution, with the promise of considerably improved performance in the future. This is being investigated as a general purpose timing diagnostic for experiments.

o After a conceptual design was completed at SLAC, last quarter engineering responsibility for the hard X-ray seeding system was transferred to ANL, though SLAC will likely remain responsible for controls and commissioning.

o Short bunch (few-femtosecond) operation of the LCLS based on low charge (20-40pc) and the slotted spoiler is regularly used by experimenters, however the existing diagnostics cannot resolve bunches below 20 femtoseconds. Last quarter a conceptual and optical design of a single shot broad-band (6-50um) infra-red spectrometer for bunch length measurement was completed. This system will be constructed and initial testing is expected next quarter. An upgrade to the slotted foil system is also under development.

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o The assembly and vacuum testing of the thermal-acoustic X-ray energy monitor was completed last quarter. Next quarter the system is planned to be installed and commissioned to provide absolute X-ray flux measurements

o Last quarter the LCLS THz system was commissioned with THz energies up to 140 J. Initial demonstration measurements showed non-linear absorption in GaAs, physics not accessible with any other source.

o Last quarter materials testing in the X-ray diagnostics chamber allowed the selection of several materials for use as X-ray attenuators. Next quarter the Be attenuators in the FEE are expected to be replaced with diamond and sapphire to reduce X-ray beam distortions.

LCLS_II: The LCLS_II is a project to construct a new XFEL facility at SLAC to provide additional capacity for more simultaneous user experiments.

o The layout of the LCLS_II undulators and X-ray system was completed last quarter. The extended soft X-ray wavelength range of the LCLS_II introduces significant damage issues for stoppers and mirrors resulting in complex design trade-offs.

o Conceptual designs for the LCLS_II gas attenuator and X-ray beam stopper systems were also completed last quarter.

o Next quarter we expect the LCLS_II CDR to be completed.

LHC: Large Hadron Collider at CERN.

o The LHC synchrotron light monitor is used to measure beam profiles and to detect particles in the abort gap. Last quarter this system was operated successfully with Lead ions. Work is underway to upgrade the optical system to provide halo measurements, with initial results expected next quarter.

o The forward proton detector system at LHC requires few-picosecond timing stability over several hundred meters. Last quarter a copy of the coax distribution system developed for LCLS demonstrated the required stability (scaled with cable length). Next quarter the system will be tested with the full 500M cable length required for the LHC.

o Last quarter the DCCT used to measure average current showed fill-pattern sensitivity. This was traced to saturation in the feedback gain chain as well as to inadequate high frequency RF bypassing of the ceramic gap. These are being fixed in the present shutdown via a re-partitioning of the gain profile and improvement of the RF bypass with an increase of capacitance and (probably) the addition of a passive ferrite ring. A further potential problem in the feedback gain/phase distribution has been identified and potential solutions investigated. The LHC fast current transformer showed position sensitivity, the cause of which has been identified, and solutions are being investigated.

6. Test Facilities

The mission of the Test Facilities Department (TFD) is to operate and support the test facilities at SLAC that are utilized to develop and test near-term solutions for accelerator issues. RF structures and power sources as well as beam optical, diagnostic and collimation systems are tested in these facilities. The major test facilities are the Next Linear Collider Test Accelerator (NLCTA), Accelerator Structure Test Area (ASTA), and L-band RF test facilities at End Station B. TFD also supports the operation of FACET, End Station A (ESA), and the ATF/ATF2 program at KEK and works closely with the Klystron and the Power Conversion R&D groups.

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ASTA report: The ASTA facility includes two s-band 50 MW klystrons who output can be combined, a variable length pulse compressor with an output of up to 500 MW and an extremely flexible RF system that is well suited for fast turnaround of experiments. The ASTA bunker’s shielding is rated for up 100 MeV beam energies. At present is used extensively for testing of all sorts of short RF structures and for testing materials that can be used in RF structure manufacture. With a modest upgrade ASTA can be used to test RF guns. The past quarter activities in ASTA were:

o Operations for the High Gradient structure tests (see also AARD-Microwave report, PETS2 and C10-VG0.7.5).

o Planning for relocation of the cryogenic test stand into the ASTA vault.o Planning for upgrading facility for 24/7 and for remote operations from the

NLCTA control room. 24/7 operation requires design and installation of a fire-suppression system for the modulators. Remote operations require upgrading the ASTA control system to EPICS and upgrading the monitoring systems for remote readout and display. Parts for the remote operation of ASTA have been purchased and are being installed. The fire suppression system is under design review by SLAC.

o A design for a spectrometer magnet can be use to characterize dark current coming out of an RF gun.

NLCTA report: The NLCTA facility is housed in End Station B (ESB). At its heart is a former 320 MeV x-band linac (from the NLC project) with an s-band injector and an output beam line and dump. The accelerator components are in their own enclosure inside the ESB hall. The past quarter activities using NLCTA were:

o Provide beam for E163 and the ECHO experiments (see also AARD-Laser for more E163 information).

o An experiment to generate THz radiation was conducted, but was unsuccessful.o A CSR experiment (in collaboration with UCLA) had its first run.o Provide a home for testing x-band RF.

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o Revived the x-band two-pack for plasma switch testing and for future use in the NLCTA accelerator.

o Start upgrading the NLCTA beam line with addition of two transverse cavities for improved slice emittance measurement for the ECHO-7 experiment.

o Start the design of a new x-band test station in the beam dump area. This station will have an x-band gun and some beam acceleration capability.

FACET User Area report: In anticipation of FACET construction completion, planning on the experimental user area and the purchase of a trailer for FACET users is proceeding.

End Station A: It is planned to have a new electron test beam in ESA (End Station Test Beam, ESTB). First operation of the ESTB is expected in summer of 2011. This test beam will provide the full range of electron energies up to 13.6 GeV, and intensities from single particles to .25 nC/ bunch. It will be used primarily for detector R&D and machine developments. The designs for kicker magnets and ceramic beam pipes to extract and transport beam from the LCLS linac to ESA have been completed and are being fabricated. The design for the PPS system for ESA and procurement of PPS parts has been started. A one day workshop will be held on March 17, 2011 to disseminate information about ESTB capabilities and progress and to ascertain user interest.

End Station B: In addition to housing the NLCTA, ESB also supports a range of high power RF source development activities (in collaboration with the Accelerator Design Department and others).

o MARX modulator testing. The failure of the MARX modulator capacitors under full load has led to a study to measure capacitor aging. In the meanwhile the MARX modulator is being run at reduced pulse width but with same power.

o The Cluster-Klystron concept prototype was installed on the NLCTA enclosure roof and tested. Planning for a full scale test (160 meter big pipe) installed in the ESB has started.

o The two-pack system LLRF has been upgraded and modulator mods have been made to facilitate design testing by AED’s Power Conversion Department. A fire suppression system for the two-pack system has been installed.

o TTF3 coupler testing.

ECHO Experiment: Echo-7 is a proof-of-principle echo-enabled harmonic generation (EEHG) experiment which is being performed at the NLCTA at SLAC. The experiment aims to test the physics of the EEHG concept and demonstrate scaling. The 3rd, 4th, 5th, 7th, and possibly 15th harmonic of a 1590nm seed laser will be generated through the EEHG scheme. In contrast to other schemes for generating harmonic bunching (e.g. HGHG), higher harmonics can potentially be reached with EEHG; in fact, due to the remarkable up-conversion efficiency, soft x-rays may be reached directly from a UV seed laser.

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o After a successful summer run which provided a qualitative confirmation of the ECHO theory, planning for an experiment aimed at making quantitative measurements by summer of 2011 are underway

7. FACET Construction

The FACET project received CD2/3 approval in July, 2010 and established a baseline as of the end of September. In that baseline, the project was 59% complete and held 2.1M$ of management reserve on an estimated cost to complete of $5M. During Q1 FY2011, installation began on cable plant, support stands and vacuum infrastructure. Controls and power supply racks were pre-assembled in the rack factory, transported out to klystron gallery and installed, leaving only final connections to be made. Two additions to the project scope were approved, the personnel protection system modifications needed for FACET and the experimental users trailer, for a total of about $500K. At the end of the quarter, the project was 80% complete and held 1.3M$ of management reserve on an estimated cost to complete of 2.6M$. The FACET installation in Sector 20 is expected to complete in April, 2011.

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