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

2 Option: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,

3 Option: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 High T, large r i, Debye shielding riri Little experimental data exist for any plasmas No data exist in the warm dense regime “strong coupling” affects all collisional processes: particle transport EOS opacity

4 Option:UCRL# Option:Directorate/Department Additional Information Plasmas in this regime have great uncertainty in the population of bound states

5 Option:UCRL# Option:Directorate/Department Additional Information So what are the REALLY BIG question in non-ideal plasma physics? Electrical conductivity (AC) Electrical conductivity (DC) Thermal Conductivity Opacity (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

6 Option:UCRL# Option:Directorate/Department Additional Information Opacity: Measuring high temperature opacities is extremely difficult  High temperature opacities require several components 1.Minimal spatial gradients in temperature and density 2.Temporal resolution to resolve changes in density and temperature 3.Spectral resolving power to resolve spectral features 4.Source emission 5.Bright and relatively uniform backlighter

7 Option:UCRL# Option:Directorate/Department Additional Information Opacity:High temperature opacities could be obtained using emission spectroscopy Early experiments suggest buried layers approach near LTE conditions energy (KeV) NLTE STA LTE STA USP DATA 1000A CH / 200A Ge emission x emission NLTE STA LTE STA USP DATA x A 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 foil Energetic x-rays X-ray spectrometer

8 Option:UCRL# Option:Directorate/Department Additional Information 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.

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

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

11 Option:UCRL# Option:Directorate/Department Additional Information 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:- Where: n e C ij is the collisional excitation rate coefficient; A ji is the spontaneous radiative decay coefficient; n e electron density (/cc);  E ij is the transition energy (keV) T e is the electron temperature (keV). Courtesy of David Hoarty

12 Option:UCRL# Option:Directorate/Department Additional Information Opacity:Experimental layout for the compressed target experiments Courtesy of David Hoarty

13 Option:UCRL# Option:Directorate/Department Additional Information Opacity: Results of shocked Ge suggests data is much closer to LTE Courtesy of David Hoarty

14 Option:UCRL# Option:Directorate/Department Additional Information 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 Probe protons Heating protons

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

16 Option:UCRL# Option:Directorate/Department Additional Information HYDRA was used to simulate the heating from the measured proton spectrum

17 Option:UCRL# Option:Directorate/Department Additional Information Simulations suggest “uniform” heating using our proton spectrum 5 micron thick

18 Option:UCRL# Option:Directorate/Department Additional Information Audebert, et. al. PRE, 2001; 64: Time (ps) Phase (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 Δ  expansion velocity V  Δ t -> density Isothermal expansion ->temperature-> Z * 100  m 20 ps

19 Option:UCRL# Option:Directorate/Department Additional Information The ionization dynamics of the carbon is critical to understanding the stopping power Ionization balance calculated using FLYCHK Solid density Stewart-Pyatt continuum lowering The bound electron stopping is dominated by the C 2+ charge state. For our plasma we have: Free electron stopping is in a partially degenerate gas eV Ionization balance 20 eV Ionization balance Charge state Relative population

20 Option:UCRL# Option:Directorate/Department Additional Information Comparison to theories and the MD simulations Early MD simulations were performed with higher T e. 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.

21 Option:UCRL# Option:Directorate/Department Additional Information EOS-For EOS use LCLS for isochoric heating of solid matter and measure release velocity  70fs deposition of 10 12, 4500eV photons LCLS 4.5keV 1.0 µm Ag Schematic of the experiment Known deposition mechanis m Transmission 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

22 Option:UCRL# Option:Directorate/Department Additional Information 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 beam K-shell spectrometer XUV spectrometer Transmitted x-rays Material: Silver

23 Option:UCRL# Option:Directorate/Department Additional Information EOS-LCLS data is promising but still is under analysis

24 Option:UCRL# Option:Directorate/Department Additional Information SUMMARY-But our success has been somewhat limited and as Clint says… We must know our limitations!!!!

25 Option:UCRL# Option:Directorate/Department Additional Information So what have high intensity lasers REALLY taught us about HED plasmas REALLY BIG areas of interestPW lasersXFELBoth Electrical 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 --- ☺

26 Option:UCRL# Option:Directorate/Department Additional Information 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 !!!

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