Effect of injection conditions on the non-linear behavior of the ECDI and related turbulent transport

TL;DR

This study revisits the classical theory of the electron-cyclotron drift instability (ECDI) through kinetic simulations, revealing long-term behaviors, the impact of injection conditions, and the potential for sustained turbulent transport in plasma systems.

Contribution

It demonstrates that injection conditions significantly influence the non-linear evolution and sustained oscillations of ECDI, extending understanding beyond previous periodic boundary analyses.

Findings

Long-term plasma tends to a new equilibrium with mild oscillations.

Injection conditions affect the stability and oscillation regimes of ECDI.

Sustained oscillations occur when ion residence time matches saturation time.

Abstract

The electron-cyclotron drift instability (ECDI) has been proposed as one of the main actors behind the anomalous transport of electrons in Hall plasmas. In this work, we revisit the classical theory of this instability [Forslund et al., Phys. Rev. Lett. 25, 1266 (1970)] and perform two-dimensional kinetic simulations under several conditions to analyze the non-linear behavior and the induced transport. Fully-periodic simulations, with conditions faithful to the linear theory are analyzed first. In agreement with existing literature, they show the growth of ECDI modes, ion-wave trapping vortexes and an induced cross-field electron current in early simulation times. However, in contrast with similar works, non-linear saturation is observed and the plasma tends, in the long term, to a new equilibrium with mild oscillations and mild anomalous current. This evolution is consistent to what can be expected from energy conservation. The quenching of the oscillations seem to be highly related with the distortion of ion vortexes in phase space after a long-term interaction with the electrostatic wave. This result suggests that sustained oscillations and turbulent current could thrive if ions are renewed by, e.g., removing and injecting particles through axial boundaries instead of applying periodicity.This second type of simulations shows that injection conditions highly impact the late simulation behavior of ECDI oscillations, where we identify several regimes depending on the value of the ion residence time compared to the characteristic saturation time in the fully periodic case. The intermediate regime, where these two times are close, is the only one providing sustained oscillations and electron transport.