Description
Shocks are fundamental drivers of energy dissipation in both astrophysical and laboratory plasmas. A quantitative understanding of how shock dynamics evolve as particle collisions become infrequent, transitioning from collisional to collisionless regimes, remains a frontier problem. Even in the collisional regime, the thermal precursor acts as a critical region where non-thermal effects may emerge [1, 2]. Non-thermal ions can counter-stream against the bulk flow, modifying the shock structure and potentially driving kinetic instabilities.
We present high-resolution, time-resolved measurements of shock profiles with Mach numbers ranging from 3 to 5, obtained from experiments at the LULI2000 and GEKKO XII facilities. Using collective optical Thomson scattering, we have mapped the evolution of electron and ion temperatures and densities to resolve both the forward and a reverse shock with unprecedented detail. To analyze these data, we developed a Bayesian analysis framework that self-consistently accounts for multiple ion species, resolving their individual temperatures and relative fractions.
To interpret the experimental results, we employ a dual-modeling approach: extended-MHD[3] simulations to capture large-scale plasma dynamics and fully kinetic particle-in-cell simulations[4] to isolate the underlying microphysics. Our results reveal a broad forward shock transition and significant interpenetration between the piston and the background plasma in the downstream region. Furthermore, we observe strong heating of the carbon population immediately ahead of the forward shock, suggesting a significant modification of the energy partition across the shock front driven by kinetic ion behavior.
References:
[1] Vidal, F. et al. Phys. Fluids B (1993).
[2] Rinderknecht, H. G. et al. Phys. Rev. Lett. 120 (2018).
[3] Fryxell, B. et al. Astrophys. J. Suppl. Ser. 131 (2000).
[4] Derouillat, J. et al. Comput. Phys. Commun. 222, 351–373 (2018).