Electron-Driven Instabilities in the Solar Wind

• DOI: 10.3389/fspas.2022.951628
• Publication Date: 2022-08-03T05:06:25Z
• Authors: Daniel Verscharen; B. D. G. Chandran; E. Boella; J. Halekas; M. E. Innocenti; V. K. Jagarlamudi; A. Micera; V. Pierrard; Š. Štverák; I. Y. Vasko; M. Velli; P. L. Whittlesey
• Keywords: Solar wind; quasi-linear theory; Astronomy; Geophysics. Cosmic physics; heat flux; FOS: Physical sciences; Electrons; QB1-991; 530; 01 natural sciences; 7. Clean energy; Physics - Geophysics; Plasma; Physics - Space Physics; 0103 physical sciences; plasma; Solar and Stellar Astrophysics (astro-ph.SR); QC801-809; electrons; Astronomy and Astrophysics; 520; Physics - Plasma Physics; Space Physics (physics.space-ph); Geophysics (physics.geo-ph); Plasma Physics (physics.plasm-ph); Quasi-linear theory; temperature anisotropy; solar wind; Astrophysics - Solar and Stellar Astrophysics; instabilities; 13. Climate action

The electrons are an essential particle species in the solar wind. They often exhibit non-equilibrium features in their velocity distribution function. These include temperature anisotropies, tails (kurtosis), and reflectional asymmetries (skewness), which contribute a significant heat flux to the solar wind. If these non-equilibrium features are sufficiently strong, they drive kinetic micro-instabilities. We develop a semi-graphical framework based on the equations of quasi-linear theory to describe electron-driven instabilities in the solar wind. We apply our framework to resonant instabilities driven by temperature anisotropies. These include the electron whistler anisotropy instability and the propagating electron firehose instability. We then describe resonant instabilities driven by reflectional asymmetries in the electron distribution function. These include the electron/ion-acoustic, kinetic Alfvén heat-flux, Langmuir, electron-beam, electron/ion-cyclotron, electron/electron-acoustic, whistler heat-flux, oblique fast-magnetosonic/whistler, lower-hybrid fan, and electron-deficit whistler instability. We briefly comment on non-resonant instabilities driven by electron temperature anisotropies such as the mirror-mode and the non-propagating firehose instability. We conclude our review with a list of open research topics in the field of electron-driven instabilities in the solar wind.