Electron acceleration driven by the lower-hybrid-drift instability

Federico Lavorenti,Nicolas André,Francesco Califano,Sae Aizawa,Pierre Henri

doi:10.1051/0004-6361/202141049

Abstract

Context.Density inhomogeneities are ubiquitous in space and astrophysical plasmas, particularly at contact boundaries between different media. They often correspond to regions that exhibit strong dynamics across a wide range of spatial and temporal scales. Indeed, density inhomogeneities are a source of free energy that can drive various instabilities such as the lower-hybrid-drift instability, which, in turn, transfers energy to the particles through wave-particle interactions and eventually heats the plasma.Aims.Our study is aimed at quantifying the efficiency of the lower-hybrid-drift instability to accelerate or heat electrons parallel to the ambient magnetic field.Methods.We combine two complementary methods: full-kinetic and quasilinear models.Results.We report self-consistent evidence of electron acceleration driven by the development of the lower-hybrid-drift instability using 3D-3V full-kinetic numerical simulations. The efficiency of the observed acceleration cannot be explained by standard quasilinear theory. For this reason, we have developed an extended quasilinear model that is able to quantitatively predict the interaction between lower-hybrid fluctuations and electrons on long time scales, which is now in agreement with full-kinetic simulations results. Finally, we apply this new, extended quasilinear model to a specific inhomogeneous space plasma boundary, namely, the magnetopause of Mercury. Furthermore, we discuss our quantitative predictions of electron acceleration to support future BepiColombo observations.

Highlights

Inhomogeneities in the magnetic field, velocity, density, temperature, etc. from fluid down to kinetic scales are commonly encountered in space and astrophysical plasmas (Amatucci 1999)
We present the first direct numerical evidence of lower-hybrid-drift instability (LHDI) electron acceleration from full-kinetic 3D-3V simulations, and we build up an extended quasilinear model that takes into account the effect of such nonlinear saturation to quantitatively estimate electron acceleration under realistic space plasma parameters
In order to overcome the intrinsic limits of the standard quasilinear theory, we build an extended quasilinear model that includes the consequences of nonlinear LD-like effects

Summary

Introduction

Inhomogeneities in the magnetic field, velocity, density, temperature, etc. from fluid down to kinetic scales are commonly encountered in space and astrophysical plasmas (Amatucci 1999). Ωciωce/2π, are ubiquitous in magnetized space plasma environments Such waves are commonly observed at Earth’s magnetotail (Huba et al 1978; Retinó et al 2008; Zhou et al 2009, 2014; Khotyaintsev et al 2011; Norgren et al 2012; Le Contel et al 2017) and Earth’s magnetopause (André et al 2001; Bale et al 2002; Vaivads et al 2004; Graham et al 2017, 2019; Tang et al 2020). In these two regions, LHW are commonly observed in the vicinity of magnetic reconnection sites where strong density gradients do form. Their role on the onset (or relaxation) of magnetic reconnection has been addressed in the past and still represents a key point in the context of reconnection research (Daughton 2003; Lapenta et al 2003, 2018; Yoo et al 2020)

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