Bump-on-tail instability across coupling and interaction-range regimes

Joseph J Williams,James Hamilton Cooley,Mathieu Marciante,Michael S Murillo,Gautham Dharuman

doi:10.1103/physrevresearch.1.033166

Abstract

The authors study the bump-on tail instability using molecular dynamics to explore the roles of collisionality, correlations and the effective interparticle force law across wide ranges of plasma temperatures, densities and charge states, and show that, even with a small number of point particles, the results are robust.

Highlights

Kinetic and fluid instabilities are distinguishing features of most plasmas, including those that appear in the solar wind [1], inertial-confinement fusion experiments [2], material processing [3], neutron-star magnetospheres [4], earth’s foreshock region [5,6], and tokamaks [7], among many other examples
Because these instabilities occur in a wide range of plasmas, including those with various levels of collisionality and containing various species, it is important to examine in detail the role of different types of interparticle interactions and varying levels of collisionality and interparticle correlations
We found agreement between the predictions of the dispersion relation and the molecular dynamics (MD) results

Summary

INTRODUCTION

Kinetic and fluid instabilities are distinguishing features of most plasmas, including those that appear in the solar wind [1], inertial-confinement fusion experiments [2], material processing [3], neutron-star magnetospheres [4], earth’s foreshock region [5,6], and tokamaks [7], among many other examples. A common type of instability is that of energy conversion from a directed current into random thermal motion; examples of this type of instability are the two-stream and bump-on-tail (BOT) instabilities Work on this class of instabilities was carried out by Bunemen, who examined electron currents colliding with initially stationary ions [8,9] and found rapid clustering of ions that destroyed these currents within a few plasma periods. Dressed ion-ion collisions in the two-stream instability in thermonuclear plasmas using Krook models [10] and examined anomalous absorption of radiation energy by electrons using Fokker-Planck models [11] In their seminal work, Takizuka and Abe [12] developed a method for including collisions in plasma simulations.

THEORETICAL MODEL

RESULTS

SUMMARY AND CONCLUSIONS