Interaction of a Relativistic Magnetized Collisionless Shock with a Dense Clump

TL;DR

This study uses advanced simulations to explore how dense clumps interact with relativistic magnetized shocks, revealing particle escape and deceleration effects that limit magnetic field amplification.

Contribution

First combined 2D PIC and MHD simulations to analyze dense clump-shock interactions in relativistic plasmas, highlighting kinetic effects and large-scale behaviors.

Findings

Particles escape along magnetic field lines reducing vorticity.

Shocked clump rapidly decelerates due to relativistic effects.

Magnetic field amplification is limited by particle escape and deceleration.

Abstract

The interactions between a relativistic magnetized collisionless shock and dense clumps have been expected to play a crucial role on the magnetic field amplification and cosmic-ray acceleration. We investigate this process by two-dimensional Particle-In-Cell (PIC) simulations for the first time, where the clump size is much larger than the gyroradius of downstream particles. We also perform relativistic magnetohydrodynamic (MHD) simulations for the same condition to see the kinetic effects. We find that particles escape from the shocked clump along magnetic field lines in the PIC simulations, so that the vorticity is lower than that in the MHD simulations. Moreover, in both the PIC and MHD simulations, the shocked clump quickly decelerates because of relativistic effects. Owing to the escape and the deceleration, the shocked clump cannot amplify the downstream magnetic field in relativistic collisionless shocks. This large-scale PIC simulation opens a new window to understand large-scale behaviors in collisionless plasma systems.