Ion sound instability driven by ion beam

TL;DR

This paper investigates ion sound instabilities caused by ion beams in finite systems, revealing how boundary reflections and dispersion effects influence stability through analytical and numerical analysis.

Contribution

It provides a combined analytical and numerical study of ion sound instabilities in finite systems with ion flow, highlighting the role of boundary reflections and dispersion.

Findings

Boundary reflections induce coupling of energy modes leading to instability.

Dispersion effects due to system length and Debye length are crucial for stability.

Analytical results agree with numerical simulations.

Abstract

Ion sound instabilities driven by the ion flow in a system of a finite length are considered by analytical and numerical methods. The ion sound waves are modified by the presence of stationary ion flow resulting in negative and positive energy modes. The instability develops due to coupling of negative and positive energy modes mediated by reflections from the boundary. It is shown that the wave dispersion due to deviation from quasineutrality is crucial for the stability. In finite length system, the dispersion is characterized by the length of the system measured in units of the Debye length. The instability is studied analytically and the results are compared with direct, initial value numerical simulations.