A Generalized Boltzmann Kinetic Theory for Strongly Magnetized Plasmas with Application to Friction

TL;DR

This paper develops a unified kinetic theory for Coulomb collisions in plasmas across all magnetization levels, revealing new transverse friction effects in strongly magnetized regimes.

Contribution

It introduces a generalized collision operator that spans from weak to strong magnetization, extending previous theories and predicting novel transverse friction forces.

Findings

The theory predicts a transverse friction component in strongly magnetized plasmas.

Good agreement with linear response theory in overlapping regimes.

Applicable to regimes beyond linear response theory's validity.

Abstract

Coulomb collisions in plasmas are typically modeled using the Boltzmann collision operator, or its variants, which apply to weakly magnetized plasmas in which the typical gyroradius of particles significantly exceeds the Debye length. Conversely, O'Neil has developed a kinetic theory to treat plasmas that are so strongly magnetized that the typical gyroradius of particles is much smaller than the distance of closest approach in a binary collision. Here, we develop a generalized collision operator that applies across the full range of magnetization strength. To demonstrate novel physics associated with strong magnetization, it is used to compute the friction force on a massive test charge. In addition to the traditional stopping power component, this is found to exhibit a transverse component that is perpendicular to both the velocity and Lorentz force vectors in the strongly magnetized regime, as was predicted recently using linear response theory. Good agreement is found between the collision theory and linear response theory in the regime in which both apply, but the new collision theory also applies to stronger magnetization strength regimes than the linear response theory is expected to apply in.