From Weibel seeds to collisionless dynamos beyond pair-plasmas

TL;DR

This study uses advanced collisionless turbulence simulations to explore magnetic seed generation and dynamo amplification in weakly collisional plasmas, revealing how electron-ion decoupling and pressure isotropization influence magnetic field growth.

Contribution

It introduces a novel simulation approach with an ion-to-electron mass ratio of 100, capturing both seed generation and dynamo amplification beyond pair-plasma models.

Findings

Electron and ion dynamics are sufficiently decoupled at mass ratio 100.

Pressure isotropization influences the magnetic Reynolds number.

Transition between kinetic and MHD-like dynamo regimes depends on heat-flux closure.

Abstract

Bridging the spatiotemporal scales of magnetic seed field generation and subsequent dynamo amplification in the weakly collisional intracluster medium presents an extreme numerical challenge. We perform collisionless turbulence simulations with initially unmagnetized electrons that capture both magnetic seed generation via the electron Weibel instability and the ensuing dynamo amplification. Going beyond existing pair-plasma studies, we use an ion-to-electron mass ratio of 100 for which we find electron and ion dynamics are sufficiently decoupled. These simulations are enabled by the 10-moment collisionless fluid solver of Gkeyll, which evolves the full pressure tensor for all species. The electron heat-flux closure regulates pressure isotropization and effectively sets the magnetic Reynolds number. We investigate how the strength of the closure influences the transition between a regime reminiscent of previous kinetic pair-plasma simulations and a regime exhibiting dynamo behavior qualitatively similar to magnetohydrodynamics.