Coherent Structures in One-dimensional Buneman Instability Nonlinear Simulations

TL;DR

This paper presents long-duration one-dimensional PIC simulations of Buneman instability, revealing complex nonlinear phase-space structures like electron holes and coupled hole-solitons, and compares these with analytical models.

Contribution

It provides detailed simulation data of Buneman instability nonlinear evolution and develops analytical models for steady nonlinear potential structures.

Findings

High ion temperature leads to electron holes dominance.

Ion density modulation causes ion-acoustic potential perturbations.

Electron holes and coupled hole-solitons can be reflected, creating persistent potential peaks.

Abstract

Long-duration one-dimensional PIC simulations are presented of Buneman-unstable, initially Maxwellian, electron and ion distributions shifted with respect to one another, providing detailed phase-space videos of the time-dependence. The final state of high initial ion temperature cases is dominated by fast electron holes, but when initial ion temperature is less than approximately four times the electron temperature, ion density modulation produces potential perturbations of approximately ion-acoustic character, modified by the electron distribution shift. Early in the nonlinear phase, they often have electron holes trapped in them ("coupled hole-solitons": CHS). In high-available-energy cases, when major broadening of the electron distribution occurs, both electron holes and coupled hole-solitons can be reflected, giving persistent counter-propagating potential peaks. Analytical theory is presented of steady nonlinear potential structures in model nonlinear particle distribution plasmas with Buneman unstable parameters. It compares favorably in some respects with the nonlinear simulations, but not with the later phases when the electron velocity distributions are greatly modified.