Instabilities, anomalous heating, and stochastic acceleration of electrons in colliding plasmas

Abstract

The collision of two expanding plasma clouds is investigated, emphasizing instabilities and electron energization in the plasma mixing layer. This work is not only directly relevant to laboratory experiments with explosively created laser or z-pinch plasmas but may also elucidate naturally occurring plasma collisions in astrophysical or space physics contexts. In the previous publications [Malkov and Sotnikov, Phys. Plasmas 25, 102108 (2018) and Sotnikov et al., Phys. Plasmas 27, 122113 (2020)], we have studied, analytically and numerically, the flow emerging from interpenetrating coronas launched by two parallel wires vaporized in a vacuum chamber. The main foci of the studies have been on the general flow pattern and lower-hybrid and thin-shell instabilities that under certain conditions develop in the collision layer. The present paper centers around the initial phase of the interpenetration of the two plasmas. Two-stream ion–ion instability, efficient electron heating, and stochastic acceleration dominate plasma mixing at this phase. Both the adiabatic (reversible) electron heating and stochastic (irreversible) acceleration and heating mechanisms, powered by unstably driven electric fields, are considered. The irreversibility results from a combination of electron runaway acceleration in the wave electric fields and pitch-angle scattering on ions and neutrals.