Utilization of XFELs and Petawatt laser to study HED matter-ideas

Lawrence Livermore National Laboratory

Utilization of XFELs and Petawatt laser to study HED matter-ideas

A lot of people from LLNL, LULI, AWE, Universite de Bordeaux, Instituto Superior Technico, Oxford

University, LCLS/SLAC

2Option:UCRL# Option:Directorate/Department Additional Information

Outline

HED regime

What a petawatt laser brings to the table

What an XFEL brings to the table

And both together,


Warm Dense Matter

Motivation: Highly compressed or heated matter rapidly transitions through the warm dense matter (WDM) or non-ideal plasma regime

white dwarf

,51~ ii

High T, large ri, Debye shieldingri

Little experimental data exist for any plasmasNo data exist in the warm dense regime

“strong coupling” affects all collisional processes:

• particle transport• EOS• opacity

ii 1

ii P.E .K .E .

Z 2e2

rikBT, 4

3 ri

3 1ni

ii ~ 1 30,

ii ~ 1 200,

ii ~ 1 100,


Plasmas in this regime have great uncertainty in the population of bound states


So what are the REALLY BIG question in non-ideal plasma physics?

Electrical conductivity (AC)Electrical conductivity (DC)

Thermal ConductivityOpacity (line), well, …, not totally non-ideal

Opacity (Rossland mean)

Charged particle stopping

EOS at high pressures

Average ionization

Coulomb logarithm

Structure factor S(k,)Electron-ion collision frequency

Plasma effects on nuclear transitions

Everything above but with magnetic fields

1

2

3


Opacity: Measuring high temperature opacities is extremely difficult

High temperature opacities require several components1. Minimal spatial gradients in temperature and

density2. Temporal resolution to resolve changes in density

and temperature3. Spectral resolving power to resolve spectral

features4. Source emission5. Bright and relatively uniform backlighter

II0

e t


Opacity:High temperature opacities could be obtained using emission spectroscopy

Early experiments suggest buried layers approach near LTE conditions

1.81.71.61.51.41.31.2energy (KeV)

50

40

30

20

10

0NLTE STA

LTE STA

USP DATA

1000A CH / 200A Ge

emis

sion

x10-

9

120

100

80

60

40

20

0

emis

sion

NLTE STA

LTE STA

USP DATA

x10-

9

100A CH / 200A Ge

Ge buried layer experiment suggest transition to LTE

When plasma is in LTE, emission spectroscopy can be used to measure high temperature opacities

In equilibrium, Kirkoff’s law states,

HEPW laser

High-Z foilHigh-Z foil

Energetic x-rays

X-ray spectrometer

j

2h 3

c 2 e hkT or

jc 2

2h 3 e h

kT


Opacity: To perform these experiments, we must have extremely fast x-ray diagnostics-LLNL camera is one of two fast streak cameras fielded

Data will be separated by the transit-time difference of the x-rays reflecting off the two crystals

The slope appears as a result of the transit-time dispersion of the x-rays across a single crystal.

Rise-time should be prompt and sharp.


Opacity: Using larger lasers, aluminium buried layer have been heated at near solid density to temperatures up to 600eV using green light

Courtesy of David Hoarty


Comparisons of LTE Opacity codes to experiment show best fit at a temperature ~ 20% lower than CRE modelling. This implies the germanium sample is not in LTE.



Opacity:To achieve conditions closer to LTE we can increase the density

For LTE collisions dominate radiative transitions –the ratio of collisional rates/ radiative rates can be expressed as:-

eTijExen

jiAijCen

3.13103.1

)(

Where: neCij is the collisional excitation rate coefficient; Aji is the spontaneous radiative decay coefficient; ne electron density (/cc); Eij is the transition energy (keV) Te is the electron temperature (keV).

800eV NLTE vs LTE Ionisation for Germanium (Z=32)

2.60E+01

2.70E+01

2.80E+01

2.90E+01

3.00E+01

0 2 4 6 8 10

Density (g/cc)Zb

ar LTE

NLTE



Opacity:Experimental layout for the compressed target experiments



Opacity: Results of shocked Ge suggests data is much closer to LTE



Petawatt lasers: Use short pulse laser generated protons to heat sample and short pulse laser generated protons to measure energy loss

Basic concept of experiment:• Short pulse laser generated protons have a short pulse duration.

They also have a long mean free path. Thus they are a good candidate for volumetric heating of material.o This minimizes hydrodynamic expansion and spatial gradients during the

stopping measurement

o The short proton pulse duration allows one to probe during a snap-shot of the plasma characteristics

Probeprotons

Heatingprotons


Petawatt laser: Proton stopping power in strongly coupled plasma is performed using TNSAed protons

Protons heat edge-on• Typical heating energy~130 J• Typical probe energy~20 J

Proton spectrometer measures heating spectrum

• Spectrum is used to infer temperature

FDI measures expansion of critical surface

• Expansion velocity is used to infer temperature


HYDRA was used to simulate the heating from the measured proton spectrum


Simulations suggest “uniform” heating using our proton spectrum

5 micron thick


Audebert, et. al. PRE, 2001; 64: 0564120

-5

-10

-15

-20-10 -5 0 5 10Time (ps)Ph

ase

(rad

)

Methodology: Use Fourier domain interferometry to determine the target characteristics

Fourier Domain Interferometry (FDI)

FDI is a well Established Technique

• Use beam splitter and delay line control scale length

• Produce phase as a function of time• Φ(t)≈expansion velocity• V • t -> density• Isothermal expansion ->temperature-> Z*

l

100 um

20 ps


The ionization dynamics of the carbon is critical to understanding the stopping power

S B 1 Z Z a( )ln b n n Z Z a( )ln f

B 4e4 NZ a mV 2 , b n 2mV 2 I z n, f 2mV 2 I f , Z a atomic number

N plasma density, V proton velocity, Z average ionization

I z nionization potential , I f Ze2 lD

• Ionization balance calculated using FLYCHK• Solid density• Stewart-Pyatt continuum lowering

• The bound electron stopping is dominated bythe C2+ charge state.

• • For our plasma we have:

ii 5, ie 2, Fermi 0.84

Free electron stopping is in a partially degenerate gas

0 1 2 3 4 5 6

0.8

0.7

0.6

0.3

0.4

0.5

0.2

0.1

0.0

15 eV Ionization balance20 eV Ionization balance

Charge state

Rel

ativ

e po

pula

tion


Comparison to theories and the MD simulations

• Early MD simulations were performed with higher Te. However the difference in temperature results in a minor change in average ionization (70% vs 83% C+2). dE/dx has been inferred using the 2.5µm energy shift data, where peak is shown to shift.

Data is adequate to determine the need for quantum atomic physics in MD code but better data is need to distinguish between models.


EOS-For EOS use LCLS for isochoric heating of solid matter and measure release velocity

70fs deposition of 1012, 4500eV photons

LCLS 4.5keV

1.0 µm Ag

Schematic of the experiment

Known deposition mechanis

mTransmission measurement

• Calculate initial energy density (J/g)

• Assume LTE

• Use Sesame EOS to determine T, P

• Use initial condition to drive radiation hydrodynamic simulation

* Courtesy of Dr. Dick Lee, LCLS


EOS-Recently we performed an experiment at LCLS to determine the off-Hugoniot EOS of HED Ag

Need to determine f(ρ,V,T) Isochoric heating of solid target using XFEL beam Infer absorbed energy Infer peak temperature Measure effects of pressure on bound states

LCLS beam

FDI beamFDI beam

K-shell spectrometer XUV spectrometer

Transmitted x-rays

Material: Silver


EOS-LCLS data is promising but still is under analysis


SUMMARY-But our success has been somewhat limited and as Clint says…

We must know our limitations!!!!


So what have high intensity lasers REALLY taught us about HED plasmas

REALLY BIG areas of interest PW lasers XFEL BothElectrical conductivity (AC) ?Electrical conductivity (DC) --- --- ?Thermal Conductivity --- ?Opacity (line) --- ☺Opacity (Rossland mean) --- --- ?Charged particle stopping --- ☺EOS at high pressures --- ?Coulomb logarithm --- --- ?Structure factor S(k,) --- ?Electron-ion collision frequency --- --- ?Plasma effects on nuclear transitions Ideas only --- ☺Everything above but with magnetic fields --- --- ☺


Petawatt + XFEL, … hmmm, ideas that still need vetting

Verify Kirkoff law for buried laser experiments The petawatt provides the capability of a large, short burst of

charged particles (charged particle stopping)• Clean rear surface to eliminate proton acceleration• Select specific ions• Photoexcite specific meta-stable states• Inject into isochoric heated solid

Simultaneous x-ray probing with visible light probing (e-i equilibration ??)• XFEL heating of solid• FDI + Thomson scattering

FDI measures electron motion X-rays measure lattice expansion using “Debye-Waller”

MAGNETIC FIELDS and Frequency doubled light !!!


Conclusion

High intensity, short pulse laser have already made a contribution to understanding non-ideal, HED plasma physics

However, there is a lot of work to be done

A new facility should help address the “BIG” issue in the field !!

In addition to a petawatt laser and XFEL, I think you need a well characterized source of magnetic field

Utilization of XFELs and Petawatt laser to study HED matter-ideas

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