Ion dynamics and acceleration in relativistic shocks

TL;DR

This study uses relativistic particle-in-cell simulations to analyze collisionless shock properties and particle acceleration mechanisms, revealing a Fermi-like energy growth process with implications for cosmic ray generation and astrophysical phenomena.

Contribution

It provides a detailed ab-initio numerical analysis of relativistic shocks, confirming previous findings and elucidating the particle acceleration process in unmagnetized plasmas.

Findings

Reproduces shock structure and acceleration features from previous studies

Identifies a Fermi-like acceleration mechanism with increasing collision times

Highlights the relevance for cosmic ray and astrophysical shock physics

Abstract

Ab-initio numerical study of collisionless shocks in electron-ion unmagnetized plasmas is performed with fully relativistic particle in cell simulations. The main properties of the shock are shown, focusing on the implications for particle acceleration. Results from previous works with a distinct numerical framework are recovered, including the shock structure and the overall acceleration features. Particle tracking is then used to analyze in detail the particle dynamics and the acceleration process. We observe an energy growth in time that can be reproduced by a Fermi-like mechanism with a reduced number of scatterings, in which the time between collisions increases as the particle gains energy, and the average acceleration efficiency is not ideal. The in depth analysis of the underlying physics is relevant to understand the generation of high energy cosmic rays, the impact on the astrophysical shock dynamics, and the consequent emission of radiation.