A "Faux-Shock" Method for Hybrid Simulations of Astrophysical Shocks

TL;DR

This paper introduces a computationally efficient hybrid simulation method using a faux-shock boundary condition to accurately model astrophysical shocks and their precursors over long timescales.

Contribution

The authors present a novel faux-shock boundary condition for hybrid simulations that reduces computational costs while accurately reproducing shock physics.

Findings

Reproduces fluid quantities and phase spaces of traditional shock simulations

Enables long-term simulations with higher particle resolution

Reduces computational cost compared to 3D simulations

Abstract

We demonstrate a novel setup for hybrid particle-in-cell simulations designed to isolate the physics of the shock precursor over long time periods for significantly lower computational cost than previous methods. This is achieved using a "faux-shock" or shock-like boundary condition on one edge of our simulation domain such that particles that interact with the boundary either pass through it or are reflected off of it with a change in momentum that mimics scattering in the downstream. We show that our faux-shock setup reproduces the same fluid quantities and phase spaces as traditional shock simulations, including those which could otherwise only be done in 3D, with higher particle resolution and for reduced computational cost. While the method involves an assumed boundary condition, it nonetheless captures the essential physics of interest, establishing it as a reliable and efficient tool for future self-consistent studies of instabilities driven by cosmic rays in a shock upstream medium.