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

1. 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. Outline • HED regime • What a petawattlaser brings to the table • What an XFEL brings to the table • And both together,

3. Warm Dense Matter ri High T, large ri, Debye shielding “strong coupling” affects all collisional processes: • particle transport • EOS • opacity Little experimental data exist for any plasmas No data exist in the warm dense regime white dwarf Motivation: Highly compressed or heated matter rapidly transitions through the warm dense matter (WDM) or non-ideal plasma regime

4. Plasmas in thisregime have greatuncertainty in the population of bound states

5. So what are the REALLY BIG question in non-ideal plasma physics? 1 2 3

6. Opacity: Measuring high temperature opacities is extremely difficult • High temperature opacities require several components • Minimal spatial gradients in temperature and density • Temporal resolution to resolve changes in density and temperature • Spectral resolving power to resolve spectral features • Source emission • Bright and relatively uniform backlighter

7. Ge buried layer experiment suggest transition to LTE 120 100A CH / 200A Ge 100 x10-9 LTE STA Energetic x-rays 80 HEPW laser 60 USP DATA emission 40 X-ray spectrometer 20 NLTE STA 0 High-Z foil High-Z foil 50 LTE STA 40 1000A CH / 200A Ge x10-9 30 20 USP DATA emission 10 NLTE STA 1.2 1.3 1.4 1.5 1.6 1.7 1.8 energy (KeV) 0 Opacity:High temperature opacities could be obtained using emission spectroscopy In equilibrium, Kirkoff’s law states, When plasma is in LTE, emission spectroscopy can be used to measure high temperature opacities Early experiments suggest buried layers approach near LTE conditions

8. 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. 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. 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. 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: neCij is the collisional excitation rate coefficient; Aji is the spontaneous radiative decay coefficient; ne electron density (/cc); DEij is the transition energy (keV) Te is the electron temperature (keV). Courtesy of David Hoarty

12. Opacity:Experimental layout for the compressed target experiments Courtesy of David Hoarty

13. Opacity: Results of shocked Ge suggests data is much closer to LTE Courtesy of David Hoarty

14. 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. • This minimizes hydrodynamic expansion and spatial gradients during the stopping measurement • The short proton pulse duration allows one to probe during a snap-shot of the plasma characteristics Heating protons Probe protons

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

17. Simulations suggest “uniform” heating using our proton spectrum 5 micron thick

18. Audebert, et. al. PRE, 2001; 64: 056412 FDI is a well Established Technique • Use beam splitter and delay line control scale length • Produce phase as a function of time • ΔΦ(t) ≈ expansion velocity • V • Δ t -> density • Isothermal expansion ->temperature-> Z* Methodology: Use Fourier domain interferometry to determine the target characteristics Fourier Domain Interferometry (FDI) l 0 100 um -5 Phase (rad) -10 20 ps -15 -20 -10 -5 0 5 10 Time (ps)

19. The ionization dynamics of the carbon is critical to understanding the stopping power 15 eV Ionization balance 20 eV Ionization balance 0.8 0.7 0.6 • Ionization balance calculated using FLYCHK • Solid density • Stewart-Pyatt continuum lowering • The bound electron stopping is dominated by • the C2+ charge state. Relative population 0.5 0.4 0.3 • For our plasma we have: 0.2 0.1 0 1 2 3 4 5 6 Charge state 0.0 Free electron stopping is in a partially degenerate gas

20. 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.

21. EOS-For EOS use LCLS for isochoric heating of solid matter and measure release velocity • 70fs deposition of 1012,4500eV photons Known deposition mechanism 1.0 µm Ag Transmission measurement Schematic of the experiment LCLS 4.5keV • 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. EOS-Recentlyweperformed an experimentat LCLS to determine the off-Hugoniot EOS of HED Ag • Need to determinef(ρ,V,T) • Isochoricheating of solidtargetusing XFEL beam • Inferabsorbedenergy • Inferpeaktemperature • Measureeffects of pressure on bound states XUV spectrometer K-shellspectrometer FDI beam FDI beam Transmittedx-rays LCLS beam Material: Silver

23. EOS-LCLS data is promising but still is under analysis

24. SUMMARY-But our success has been somewhat limited and as Clint says… We must know our limitations!!!!

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

26. 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. 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