Effect of strong thermalization on shock dynamical behavior

Abstract

[1] 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 (M A > 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/w pe ), while, from a macroscopic view (>several c/w pe ) 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.Citation: Shimada, N., and M. Hoshino (2005), Effect of strong thermalization on shock dynamical behavior,

Mach number dependence of electron heating in high Mach number quasiperpendicular shocks

“…They improved understandings of the process not only in terms of electron heating but also in terms of a production process of nonthermal electrons and promoted a number of subsequent simulation studies. [10][11][12][13][14][15][16][17][18][19][20][21][22] As a result, the understanding of electron heating or acceleration processes initiated by the BI in the context of the shock physics has been extensively developed.…”

On microinstabilities in the foot of high Mach number perpendicular shocks

“…It has been recognized for a long time that a variety of microinstabilities play a crucial role in wave excitation, particle heating, and anomalous dissipation mechanisms in the shock transition region [see, e.g., Papadopoulos , 1985, and references therein]. Indeed, recent full particle simulation studies revealed that a variety of microinstabilities are generated in the foot of low beta supercritical quasi‐perpendicular shocks [e.g., Shimada and Hoshino , 2000; Dieckmann et al , 2000; Hoshino and Shimada , 2002; Scholer et al , 2003; Matsukiyo and Scholer , 2003; Shimada and Hoshino , 2004; Scholer and Matsukiyo , 2004; Shimada and Hoshino , 2005; Muschietti and Lembège , 2006]. The free energy source of those microinstabilities are the relative drift between incoming electrons and reflected ions and incoming electrons and incoming ions, respectively.…”

Hybrid simulation of reforming shocks with electron mass and pressure tensor effects

“…However, in Matsukiyo and Scholer 's [2006] PIC simulation for the foot region, whistler waves did exist. Shimada and Hoshino [2004, 2005] have also shown, using PIC simulation, ion phase space holes due to wave‐particles interaction when ω pe /Ω ce is large, which implies that the generation of electromagnetic waves in the foot and ramp region should be possible.…”