utilization of xfels and petawatt laser to study hed matter-ideas
DESCRIPTION
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 . Outline. HED regime What a petawatt laser brings to the table - PowerPoint PPT PresentationTRANSCRIPT
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,
3Option:UCRL# Option:Directorate/Department Additional Information
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,
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Plasmas in this regime have great uncertainty in the population of bound states
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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
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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
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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
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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.
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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
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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.
Courtesy of David Hoarty
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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
Courtesy of David Hoarty
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Opacity:Experimental layout for the compressed target experiments
Courtesy of David Hoarty
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Opacity: Results of shocked Ge suggests data is much closer to LTE
Courtesy of David Hoarty
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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
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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
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HYDRA was used to simulate the heating from the measured proton spectrum
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Simulations suggest “uniform” heating using our proton spectrum
5 micron thick
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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
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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
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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.
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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
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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
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EOS-LCLS data is promising but still is under analysis
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SUMMARY-But our success has been somewhat limited and as Clint says…
We must know our limitations!!!!
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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 --- --- ☺
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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 !!!
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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