Effect of strong thermalization on shock dynamical behavior

Abstract

The dynamics of the perpendicular shock front is examined under various plasma parameters by using particle‐in‐cell numerical simulation. As widely accepted, above the critical Mach number (∼3) the front of (quasi‐)perpendicular shocks show nonstationary behavior due to the shock self‐reformation. In much higher Mach number regime (MA > 20), we find that dynamics of the shock front self‐reformation can be modified. Nonlinear evolution of microinstabilities in the shock transition region results turbulent profiles in a microscopic view (≤c/ωpe), while, from a macroscopic view (>several c/ωpe) because of rapid, strong thermalization in the shock transition region, the localized accumulation of the plasma due to ion dynamics is smeared out in both of the velocity phase space and real space. As a result, the shock self‐reformation is realized within a reduced time and space. We can say there is a possibility that rapid, strong dissipation helps to stabilize the macroscopic shock front dynamics; the shock self‐reformation still persists, though. The strong thermalization is caused by the nonlinear evolution of two‐stream instability between the electron and the reflected/incident ion components and following ion‐acoustic instability. We think that the modification of the shock self‐reformation process observed in high Mach number regime indicates an important role of electron kinetics and heating in the macroscopic shock front behavior.