Effect of magnetic field configuration on double layer formation and reverse discharge ignition in bipolar HiPIMS

TL;DR

This paper investigates how magnetic field configurations influence the formation of double layers and the ignition of reverse discharges in bipolar HiPIMS, revealing that magnetic balance affects ignition timing and optical emission characteristics.

Contribution

It demonstrates experimentally that magnetic field adjustments can control reverse discharge ignition timing and optical emission features in bipolar HiPIMS.

Findings

More balanced magnetic fields lead to earlier RD ignition.

Increasing the magnetic null point distance delays or prevents RD.

Optical emission varies with probe placement and magnetic configuration.

Abstract

The reverse discharge (RD) phenomenon in bipolar HiPIMS has been observed when a sufficiently long positive pulse is applied to the magnetron. Due to the magnetic field, electrons accumulated behind the magnetic trap are prevented from reaching the positive target. Consequently, a space charge double layer (DL) is formed between the positive target and the plasma behind the magnetic trap, leading to electron acceleration across the DL and RD ignition. This study reveals the significant impact of the magnetic field configuration on RD ignition. Experiments are performed using a Ti target involving magnetic field variation, wire probe measurements of floating potential, and optical emission spectroscopy imaging. It is found that adjusting the magnetic field to a more balanced configuration leads to earlier RD ignition, while a more unbalanced one delays or even prevents it. Specifically, the time of RD ignition decreases with an increase in the magnetic null point distance from the target. Moreover, the size and shape of optical emission in the RD varies with nearby probe placement, suggesting sensitivity to external electrodes.