Kinetic Simulations of Strongly-Magnetized Parallel Shocks: Deviations from MHD Jump Conditions

TL;DR

This study uses 3D kinetic simulations to explore how collisionless, strongly-magnetized shocks deviate from traditional MHD predictions, revealing important physics omitted by fluid models in astrophysical plasma systems.

Contribution

It provides detailed kinetic simulation results showing deviations from MHD jump conditions in strongly-magnetized collisionless shocks, especially at low Alfvénic Mach numbers.

Findings

Shock compression ratio decreases with increasing magnetic field strength.

Magnetic field influences shock front width significantly.

Results align with Bret & Narayan (2018) predictions.

Abstract

Shocks waves are a ubiquitous feature of many astrophysical plasma systems, and an important process for energy dissipation and transfer. The physics of these shock waves are frequently treated/modeled as a collisional, fluid MHD discontinuity, despite the fact that many shocks occur in the collisionless regime. In light of this, using fully kinetic, 3D simulations of non-relativistic, parallel propagating collisionless shocks comprised of electron-positron plasma, we detail the deviation of collisionless shocks form MHD predictions for varying magnetization/Alfv\'enic Mach numbers, with particular focus on systems with Alf\'enic Mach numbers much smaller than sonic Mach numbers. We show that the shock compression ratio decreases for sufficiently large upstream magnetic fields, in agreement with the predictions of Bret & Narayan (2018). Additionally, we examine the role of magnetic field strength on the shock front width. This work reinforces a growing body of work that suggest that modeling many astrophysical systems with only a fluid plasma description omits potentially important physics.