Precursor Wave Emission Enhanced by Weibel Instability in Relativistic Shocks

TL;DR

This study uses 2D particle-in-cell simulations to analyze precursor wave emission in relativistic shocks, revealing that Weibel instability amplifies wave power across magnetic field orientations, with implications for wakefield acceleration.

Contribution

The paper extends previous work by examining the effect of magnetic field orientation on precursor wave emission and demonstrates the role of Weibel instability in amplifying waves in relativistic shocks.

Findings

Both ordinary and extraordinary mode waves are excited.

Large-amplitude precursor waves are emitted over a wide range of magnetization.

Weibel instability amplifies wave power, especially at low magnetization.

Abstract

We investigated the precursor wave emission efficiency in magnetized purely perpendicular relativistic shocks in pair plasmas. We extended our previous study to include the dependence of upstream magnetic field orientations. We performed two-dimensional particle-in-cell simulations and focused on two magnetic field orientations: the magnetic field to be in the simulation plane (i.e., in-plane configuration) and perpendicular to the simulation plane (i.e., out-of-plane configuration). Our simulations in the in-plane configuration demonstrated that not only extraordinary but also ordinary mode waves are excited. We quantified the emission efficiency as a function of the magnetization parameter $\sigma_e$ and found that the large-amplitude precursor waves are emitted for a wide range of $\sigma_e$. We found that especially at low $\sigma_e$, the magnetic field generated by Weibel instability amplifies the ordinary mode wave power. The amplitude is large enough to perturb the upstream plasma, and transverse density filaments are generated as in the case of the out-of-plane configuration investigated in the previous study. We confirmed that our previous conclusion holds regardless of upstream magnetic field orientations with respect to the two-dimensional simulation plane. We discuss the precursor wave emission in three dimensions and the feasibility of wakefield acceleration in relativistic shocks based on our results.