Plasma effects of laser-induced shocks in flowing plasmas

High-energy lasers interacting with flowing plasmas can induce plasma responses such as beam bending and, through momentum conservation, a reduction in plasma flow velocity [1]. When an incoming supersonic plasma slows to subsonic speeds, the speckled structure of laser beams can lead to the formation of shocks within the plasma [2,3].

We report recent advances in shock modeling using both particle-in-cell (PIC) and fluid codes, alongside experimental results from the Omega facility. Key shock properties—such as density and ion temperature jumps, and propagation speed—are examined. Notably, we find good agreement among fluid and PIC simulations and experimental measurements, with shock speeds reaching approximately half the local sound speed. To reproduce this behavior, fluid models must include nonlocal electron heat conduction and collisional absorption and heating effects.

The slowing of plasma flow is described in fluid models by a drag coefficient [1,2]. This drag force arises from ion scattering off localized electrostatic fields, which are generated by the ponderomotive force and pressure variations associated with laser speckles. Due to the stochastic nature of this scattering, the lost kinetic energy of plasma’s flow is converted into ion thermal energy. Rapid ion heating has been observed in PIC simulations and confirmed experimentally by Thomson scattering in the downstream region of the laser-irradiated plasma.

[1] H.A. Rose, Phys. Plasmas 3, 1709 (1996).

[2] J. D. Ludwig, S. Hüller, H. A. Rose, C.Bruulsema, W.Farmer, P.Michel, A.Milder, G.F.Swadling, W.Rozmus, Phys. Plasmas 31 (3), 032103 (2024).

[3] A.L. Milder, C. Bruulsema, S. Hüller, C. Walsh, W. Rozmus, L. Yin, J. D. Ludwig, W. Farmer, B.J. Albright, H.A. Rose, G.F. Swadling, Phys. Rev. Res. 7, 013163 (2025).