Fast electron transport and induced heating in Aluminium foils

1. Fast electron transport and induced heating in Aluminium foils • J. J. Santos1,2, A. Debayle1, Ph. Nicolaï1, V. Tikhonchuk1, M. Manclossi2,3, D. Batani3,2, A. Guemnie-Tafo2, J. Faure2, V. Malka2, J.J. Honrubia4 • 1CELIA, Univ. Bordeaux 1, France • 2LOA, ENSTA-Polytechnique, France • 3Univ. Milano-Bicocca, Italy • 4Univ. Politécnica Madrid, Spain

2. and foot of the 2w0coherentspike 2 types of optical emission from the targets rear side 2 fast-electron components Experiment at LOA « salle jaune » — CELIA,LOA, Univ. Milano-Bicocca Th ≈ 10MeV <1% of the laser energy 40fs, 0.7J, 5 1019Wcm-2 2 10-7 contrast Coherent Transition Radiation relativistic µ-bunched and collimated electron flux 2w0 Dl ≈ 40nm Visible Visible Broad Spectrum Th ≈ 400-600keV ≈ 35% of the laser energy divergence q≈±35° Incoherent thermal emission cf. J.J. Santos et al., Phys. Plasmas, 14 (2007)

3. 10µm 20µm 50µm 100µm 2w0images @420nm (DlFWHM = 75 nm ) 100µm Visible images @525nm (DlFWHM = 90 nm ) Two fast electron components with different divergence : Relativistic electron bunches responsible for the2w0CTR signals are well collimated Spatial analysis: 2w0 and Visible light show different behaviors Thin targets effective thickness is risen by influence of the ASE pedestal ! Visible signalspractically only of thermal origin the bulk of fast electrons diverges

4. 10µm 20µm 50µm 100µm 2w0images @420nm (DlFWHM = 75 nm ) 100µm Visible images @525nm (DlFWHM = 90 nm ) Two fast electron components with different divergence : The two components have similar source sizecomparable with the laser focal spot Relativistic electron bunches responsible for the2w0CTR signals are well collimated Spatial analysis: 2w0 and Visible light show different behaviors Thin targets effective thickness is risen by influence of the ASE pedestal ! qbulk35° Visible signalspractically only of thermal origin the bulk of fast electrons diverges qtail7°

5. + fast electrons collisions with background material: Bethe-Bloch stopping power (integrated over the fast electrons VDF) Energy deposition is dominated by resistive heating at shallow depth and then by collisions Intense incident current : Ih ≈ 107 A >>IAlfven jh ≈ 1013 A/cm2 Need of a neutralizing return current: je ≈ jh ≈ sE Resistive Heating by the return current: cf. J.J. Santos et al., Phys. Plasmas, 14 (2007)

6. Pre-plasma: At shallow depth, the resistive heating by return currents is significantly enhanced Tohm  jh2 R(z)-4 ≈ 3 keV/J at 1µm depth ≈ 100 eV/J at 15µm depth Tcoll nh R(z)-2 ≈ 1.5 eV/J at 50µm depth Energy deposition is dominated by resistive heating at shallow depth and then by collisions To reproduce optical emission signals We model ASE-expanded foils rather than unperturbed solid foils cf. J.J. Santos et al., Phys. Plasmas, 14 (2007)

7. Hybrid simulation Hybrid simulation Pre-plasma: At shallow depth, the resistive heating by return currents is significantly enhanced ≈ 1.5 eV/J at 50µm depth Energy deposition is dominated by resistive heating at shallow depth and then by collisions To reproduce optical emission signals We model ASE-expanded foils rather than unperturbed solid foils Tohm  jh2 R(z)-4 ≈ 3 keV/J at 1µm depth ≈ 100 eV/J at 15µm depth Tcoll nh R(z)-2 cf. J.J. Santos et al., Phys. Plasmas, 14 (2007)

8. The experimental in-depth temperature profiles are precisely determined from the rear-side emission The experimental in-depth temperature profiles are precisely determined from the rear-side emission In-depth target heating from model(<1ps) ( R0=7.5µm , q=35° , h=35% , Th=500keV ) Thermal emission time evolution 1D hydro simulations Energy releasing of the heated plasma (Dt=5ns) ( plasma expansion, thermal diffusion, radiative transport ) Experimental datavs. integrated thermal emission Adjustement of the Te(z) profile

9. The experimental in-depth temperature profiles are precisely determined from the rear-side emission The experimental in-depth temperature profiles are precisely determined from the rear-side emission In-depth target heating from model(<1ps) ( R0=7.5µm , q=35° , h=35% , Th=500keV ) Thermal emission time evolution 1D hydro simulations Energy releasing of the heated plasma (Dt=5ns) ( plasma expansion, thermal diffusion, radiative transport ) Experimental datavs. integrated thermal emission Adjustement of the Te(z) profile Goal: converge to the experimental emission yields for all the foils

10. Inhomogeneous in-depth heating explains the intense optical emission on thin targets The experimental in-depth temperature profiles are precisely determined from the rear-side emission The experimental in-depth temperature profiles are precisely determined from the rear-side emission In-depth target heating from model ( R0=7.5µm , q=35° , h=35% , Th=500keV ) Experimental datavs. integrated thermal emission Goal: converge to the experimental emission yields for all the foils

11. Inhomogeneous in-depth heating explains the intense optical emission on thin targets The experimental in-depth temperature profiles are precisely determined from the rear-side emission The experimental in-depth temperature profiles are precisely determined from the rear-side emission In-depth target heating from model ( R0=7.5µm , q=35° , h=35% , Th=500keV ) Th=400keV Th=500keV Th=600keV Characterization of thebulk of the fast electrons : Incident current:jh≈1013 A/cm2 3-6x1012 electrons with Th ≈400-600keV (35% of the laser energy) divergence q≈ 35° Experimental datavs. integrated thermal emission

12. Fast electron propagation in high density plasmas created by shock wave compression J. J. Santos1, D. Batani2, P. McKenna3, S. D. Baton4, F. Dorchies1, A. Dubrouil1, C. Fourment1, S. Hulin1, Ph. Nicolaï1, P. Carpeggiani2, M. Veltcheva2, M. Quinn3, E. Brambrink4, M. Koenig4, M. Rabec Le Gloahec4, Ch. Spindloe5, M. Tolley5 1 CELIA, Univ. Bordeaux 1, France 2 Univ. Milano-Bicocca, Italy 3 Univ. Strathclyde, UK 4 LULI, Ec. Polytechnique, France 5 RAL, UK

13. Cu Kaimaging axis KAP conical crystal X-ray spectrometry 22.5° 45° 2w0 ns laser beam 200J over 1.5ns (flat-top), 22.5° incidence 500µm diameter (PZP  flat-top) quartz spherical crystal w0 ps laser beam 40J, 1ps (FWHM), 45° incidence 10-13µm diameter spot (f/4 OHP) 5-3x1019 Wcm-2 Interferometry axis Experiment performed at LULI pico 2000 A flat foil target is compressed by a 200J, 1.5ns beam A fast electron jet is generated by a 40J, 1ps beam

14. Fast electron propagation in high density plasmas created by shock wave compression Experiment at LULI pico 2000 — Univ. Milano-Bicocca, CELIA, Univ. Strathclyde, LULI, RAL Cu Kaimage (quartz spherical crystal; 10.8X magnification) 500µm Al and Cu spectrum (KAP conical crystal; 1.7eV spectral resolution) E Cu Ka (5th order) ns-Al plasma emission Al filter K-edge Cu 10 µm + Al 10 µm fluorescent layers Cu 20µm filter CH 10 µm CH 10 µm 40J 1ps beam 200J 1.5ns beam 45° 22.5° “propagation layer” Variable Al or CH 10 to 50 µm Be 15µm + Al 13µm filters Goals: Test fast electron propagation and energy transport - in solid vs. shock compressed targets (r  3-4rsolid ) - in dielectric (CH) vs. conductor targets (Al)

15. target with no propagation layer 40 CH propagation layer 30 Al propagation layer ns beam reference t0+4.6ns t0+3.1ns t0+1.6ns t0 r[g/cc] Shock breakout time is reproduced by 1D hydrodynamic simulations CH CH Cu Al t-t0[ns] ns beam initial position[µm] Shock breakout time measured to choose the ps/ns laser pulses delay Goal: Compress as deeper as possible, preventing from shock breakthrough before fast electron injection ns beam visible Streak camera ns beam parameters: 22.5° incidence 200J over 1.5ns (flat-top) 500µm diameter (PZP  flat-top) t [ns] 20 0

16. GOI gate=90ps wollaston A f.i.@532nm P probe beam 532nm,t=8ns Interferometry images reveal a ≈100µm pre-plasma due to the ASE-piedestal reference images ps beam tps-1100ps tps-800ps tps-300ps images with ps beam ps beam parameters: 45° incidence 40J, 1ps (FWHM) 10-13µm diameter spot Contrast:

17. As a function of the surface mass : Only compressed Al targets show a collimated transport Cu Ka images give fast electron beam divergence Typical Cu Ka images (for ps+ns interaction) Fast electron jet divergence is slightly higher in non compressed targets target with no propagation layer 500µm 10µm CH propagation layer 40µm CH propagation layer

18. Typical X-ray spectra solid vs. shock compressed targets Dielectric propagation layer Conductor propagation layer Cu Ka 1 Cu Ka 2 Cu Ka 1 Cu Ka 2 ns-Al plasma emission Al Ka ? Almost never seen… Al filter K-edge

19. Need to check with PIC simulations considering r and T-depending properties of the different target layers: - Collisional stopping power (bound and free electrons+plasmons) - Cu K shell ionization cross section - Electrical conductivity - Role of magnetic field - Electric field transport inhibition Preliminary results for the Cu Ka spectral lines integrated emission Signal yields are lower for compressed targets for both Al and CH propagation layers Without compression, signals are stronger for Al than for CH targets With compression, signal yields for Al and for CH targets are comparable

20. 2D CHIC hydrodynamic simulations account for both ns beam and ASE-pedestal (ps beam) perturbations when the UHI interactions takes place Target: 10CH-30Al-10Cu-10Al-10CH ps beam small spot size implies a 2D hydrodynamical behavior ns

21. Target: 10CH-10Al-10Cu-10Al-10CH Density profiles at 2.2ns after ns beam: UHI interaction moment ! ASE-pedestal produces non negligible effects on the propagation and fluorescent layers ASE-driven shock Even decompressed by shock breakout, the Al propagation layer is compressed to 1.5x its initial density Initial front side position