Formation of Anomalously Energetic Ions in Hollow Cathode Plume by Charge Separation Instability

TL;DR

This paper identifies a new charge separation instability mechanism in hollow cathode plumes, explaining the formation of highly energetic ions observed in experiments, which could impact electric propulsion system design.

Contribution

It introduces a novel kinetic simulation-based mechanism for energetic ion formation in hollow cathodes, challenging previous assumptions about wave-driven processes.

Findings

Charge separation instability can produce high-energy ions.

Simulations match experimental ion energy levels.

New mechanism explains observed ion energies.

Abstract

Hollow cathodes are becoming the bottleneck of many electric propulsion systems, because of the sputtering and erosion on both cathodes and thrusters from the generation of anomalously energetic ions. So far, it is believed that energetic ions are formed by waves and instabilities always accompanied in cathode discharge, but there is no evidence yet that those proposed instabilities can lead to such high ion energies measured in experiments. In this work, a new mechanism of charge separation instability in hollow cathode plume is found via fully kinetic PIC simulations, which can easily produce energetic ions to the same level as measured in experiments.