A Kinetic Model of Friction in Strongly Coupled Strongly Magnetized Plasmas

TL;DR

This paper develops a kinetic model to understand the complex friction forces acting on a test charge in strongly coupled, strongly magnetized plasmas, aligning well with molecular dynamics simulations and revealing new gyro-related effects.

Contribution

It introduces a generalized Boltzmann kinetic theory that captures multiple components of friction forces in strongly coupled, magnetized plasmas, including novel gyro effects.

Findings

The theory agrees with molecular dynamics simulations across various regimes.

A new gyro component of friction arises from short-range collision asymmetries.

Transverse forces significantly alter the test charge's trajectory and gyrofrequency.

Abstract

Plasmas that are strongly magnetized in the sense that the gyrofrequency exceeds the plasma frequency exhibit novel transport properties that are not well understood. As a representative example, we compute the friction force acting on a massive test charge moving through a strongly coupled and strongly magnetized one-component plasma using a generalized Boltzmann kinetic theory. Recent works studying the weakly coupled regime have shown that strong magnetization leads to a transverse component of the friction force that is perpendicular to both the Lorentz force and velocity of the test charge; in addition to the stopping power component aligned antiparallel to the velocity. Recent molecular dynamics simulations have also shown that strong Coulomb coupling in addition to strong magnetization gives rise to a third component of the friction force in the direction of the Lorentz force. Here, we show that the generalized Boltzmann kinetic theory captures these effects, and generally agrees well with the molecular dynamics simulations over a broad range of Coulomb coupling and magnetization strength regimes. The theory is also used to show that a "gyro" component of the friction in the direction of the Lorentz force arises due to asymmetries associated with gyromotion during short-range collisions. Computing the average motion of the test charge through the background plasma, the transverse force is found to strongly influence the trajectory by changing the gyroradius and the gyro friction force is found to slightly change the gyrofrequency of the test charge resulting in a phase shift.