Coulomb collisions in strongly anisotropic plasmas I. Cyclotron cooling in electron-ion plasmas

TL;DR

This paper analyzes the behavior of strongly anisotropic electron-ion plasmas with respect to cyclotron cooling, deriving analytical collision operators and radiation emission rates in optically thin conditions.

Contribution

It provides the first analytical calculation of the collision operator and radiation emission rate for strongly anisotropic plasmas far from Maxwellian equilibrium.

Findings

Collision operator can be calculated analytically despite anisotropy.

Radiation emission rate depends logarithmically on plasma parameters.

Electron distribution functions are characterized on various timescales.

Abstract

The behaviour of a collisional plasma which is optically thin to cyclotron radiation is considered, and the distribution functions accessible to it on the various timescales in the system are calculated. Particular attention is paid to the limit in which the collision time exceeds the radiation emission time, making the electron distribution function strongly anisotropic. Unusually for plasma physics, the collision operator can nevertheless be calculated analytically although the plasma is far from Maxwellian. The rate of radiation emission is calculated and found to be governed by the collision frequency multiplied by a factor that only depends logarithmically on plasma parameters.