The characteristic shape of emission profiles of plasma spokes in HiPIMS: the role of secondary electrons

TL;DR

This paper investigates the shape of plasma spokes in HiPIMS, linking their emission profiles to secondary electron generation and explaining material-dependent variations through electron pressure effects.

Contribution

It introduces a model connecting secondary electron generation to the characteristic shape of plasma spokes, accounting for different target materials and plasma conditions.

Findings

Emission profiles vary with target material.

Localized secondary electrons influence plasma inhomogeneities.

The model explains observed emission shapes across materials.

Abstract

A time resolved analysis of the emission of HiPIMS plasmas reveals inhomogeneities in the form of rotating spokes. The shape of these spokes is very characteristic depending on the target material. The localized enhanced light emission has been correlated with the ion production. Based on these data, the peculiar shape of the emission profiles can be explained by the localized generation of secondary electrons, resulting in an energetic electron pressure exceeding the magnetic pressure. This general picture is able to explain the observed emission profile for different target materials including gas rarefaction and second ionization potential of the sputtered elements.