The role of double ionization on the generation of doubly charged ions in copper vacuum arcs: insight from particle-in-cell/direct simulation Monte Carlo methods

TL;DR

This study uses advanced simulation methods to quantify how double ionization influences the generation and spatial distribution of doubly charged copper ions during vacuum arc breakdown, revealing nuanced effects on ion energy and distribution.

Contribution

The paper introduces a novel PIC-DSMC simulation scheme incorporating double ionization, providing a quantitative analysis of its role in vacuum arc breakdown.

Findings

Double ionization generates additional Cu2+ ions near the cathode.

Spatial distribution and energy spectra of Cu2+ ions differ with double ionization.

Cathode erosion rate matches experimental data.

Abstract

Metal vapour vacuum arcs are capable to generate multiply charged metallic ions, which are widely used in fields such as ion deposition, ion thrusters, and ion sources, etc. According to the stationary model of cathode spot, those ions are generated by electron-impact single ionization in a step-wise manner, which is M -> M+ -> M2+ -> ... mainly. This paper is designed to study quantitatively the role of double ionization M -> M2+ in the breakdown initiation of copper vacuum arcs. A direct simulation Monte Carlo (DSMC) scheme of double ionization is proposed and incorporated into a 2D particle-in-cell (PIC) method. The super-particles of Cu2+ ions generated from different channels are labelled independently in the PIC-DSMC modelling of vacuum arc breakdown. The cathode erosion rate based on PIC modelling is about 40{\mu}g/C in arc burning regime, which agrees well with previous experiments. The temporal discharge behaviours such as arc current, arc voltage, and ionization degree of arc plasma, are influenced with or without double ionization negligibly. However, additional Cu2+ ions are generated near the cathode in breakdown initiation from the double ionization channel, with a lower kinetic energy on average. Therefore, the results on spatial distribution and energy spectra of Cu2+ ions are different with or without double ionization. This paper provides a quantitative research method to evaluate the role of multiply ionization in vacuum arcs.