Kinetic simulations underestimate the effects of waves during magnetic reconnection

TL;DR

This study shows that kinetic simulations often underestimate wave effects during magnetic reconnection due to scaled parameters, impacting the accuracy of plasma behavior predictions.

Contribution

It demonstrates how reduced ion-electron mass ratios in simulations affect wave amplitudes and phase relationships, leading to underestimation of wave effects.

Findings

Wave electric field scales with 1b7b0m_i/m_e

Phase relationship of waves is altered by simulation parameters

Anomalous drag can be underestimated by an order of magnitude

Abstract

Collisionless plasma systems are often studied using fully kinetic simulations, where protons and electrons are treated as particles. Due to their computational expense, it is necessary to reduce the ion-to-electron mass ratio $m_i/m_e$ or the ratio between plasma and cyclotron frequencies in simulations of large systems. In this work we show that when electron-scale waves are present in larger-scale systems, numerical parameters affect their amplitudes and effects on the larger system. Using lower-hybrid drift waves during magnetic reconnection as an example, we find that the ratio between the wave electric field and the reconnection electric field scales like $\sqrt{m_i/m_e}$, while the phase relationship is also affected. The combination of these effects means that the anomalous drag that contributes to momentum balance in the reconnection region can be underestimated by an order of magnitude. The results are relevant to the coupling of electron-scale waves to ion-scale reconnection regions, and other systems such as collisionless shocks.