Transport of electrons in tangled magnetic fields

TL;DR

This paper reviews how electrons move in complex, tangled magnetic fields in space plasmas, highlighting the roles of turbulence, instabilities, and various plasma processes.

Contribution

It introduces fundamental principles of electron transport in tangled magnetic fields and discusses how turbulence and instabilities influence electron confinement and energization.

Findings

Electron transport is affected by magnetic field inhomogeneities and plasma processes.

Turbulence and instabilities create tangled magnetic fields that modify electron trajectories.

Multiple observational and theoretical methods are needed to understand electron transport in space plasmas.

Abstract

Cosmic magnetic fields are typically inhomogeneous and often highly tangled due to large-scale plasma flows, turbulence, and instabilities. If the variations in the magnetic field occur on scales that are large compared to the gyro-radius of the plasma electrons, the electrons are primarily confined to gyro-centre trajectories along the field lines. Therefore, in-situ electron measurements help us map out the connectivity of the magnetic field in space plasmas. Gyro-centre drifts, wave-particle interactions, trapping, and cross-field diffusion are processes related to field inhomogeneities and fluctuations; they have the potential to modify or even disrupt the transport of electrons along field lines. We introduce the basic principles of electron transport in tangled magnetic fields and review the creation of tangled fields through turbulence and instabilities as well as the modulation of parallel electron transport through kinetic instabilities. We then describe trapping and de-trapping effects in inhomogeneous magnetic fields, as well as electron diffusion and energisation across the magnetic field. The transport of electrons in tangled fields results from a complex interplay of plasma processes that occur on a broad range of scales. A combination of in-situ plasma measurements, remote-sensing plasma observations, and plasma theory and simulations is required to resolve this contemporary challenge to the fields of heliophysics and astrophysics.