Two-dimensional hybrid simulations of filamentary structures and kinetic slow waves downstream of a quasi-parallel shock

TL;DR

This study uses 2-D hybrid simulations to reveal that filamentary structures downstream of a quasi-parallel shock are caused by kinetic slow waves, characterized by specific magnetic and density fluctuations.

Contribution

It demonstrates that filamentary structures are generated by kinetic slow waves downstream of quasi-parallel shocks, supported by detailed simulation analysis and theoretical consistency.

Findings

Filamentary structures exhibit anticorrelation between magnetic field and density.

Downstream waves propagate nearly perpendicular to magnetic field with ion kinetic scale wave number.

Properties align with kinetic slow wave characteristics, confirming their role in filament formation.

Abstract

In this paper, with two-dimensional (2-D) hybrid simulations, we study the generation mechanism of filamentary structures downstream of a quasi-parallel shock. The results show that in the downstream both the amplitude of magnetic field and number density exhibit obvious filamentary structures, and the magnetic field and number density are anticorrelated. Detailed analysis find that these downstream compressive waves propagate almost perpendicular to the magnetic field, and the dominant wave number is around the inverse of ion kinetic scale. Their parallel and perpendicular components roughly satisfies(where and represent the parallel and in-plane perpendicular components of magnetic field, is the wave number in the perpendicular direction, and in the ion gyroradius), and their Alfven ratio also roughly agree with the analytical relation (where and indicate the Alfven ratio and plasma beta), while the corresponding cross helicity and compressibility show good agreement with previous theoretical calculations. All these properties are consistent with those of kinetic slow waves (KSWs). Therefore, we conclude that the filamentary structures in the downstream of a quasi-parallel shock are produced due to the excitation of KSWs.