Glow-to-arc transition in graphite cathode with high-current magnetron discharge

TL;DR

This study investigates the glow-to-arc transition in graphite cathodes within high-current magnetron discharges, revealing luminous spot formation as a key precursor, which could inform stability improvements in plasma devices.

Contribution

It provides new insights into the glow-to-arc transition mechanisms in graphite cathodes under high-current conditions using high-speed imaging and statistical analysis.

Findings

Luminous spot formation precedes arc transition.

Graphite exhibits distinct transition features compared to other refractory materials.

High-speed video analysis reveals early cathodic spot dynamics.

Abstract

The glow-to-arc transition is a critical phenomenon in plasma discharges, commonly leading to detrimental effects. The physical mechanisms triggering this transition remain poorly understood. The advent of a discharge called Hyper-Power Impulse Magnetron has opened possibilities. Hyper-Power Impulse Magnetron allows the glow mode to be maintained over long periods (1 ms) and at high-current densities (> 5 A/cm$^2$), which has unveiled certain features in the glow-to-arc transition. This work focuses on a graphite target that transits easily in the arc regime. The high-speed video-camera analysis revealed specific properties of graphite in ExB discharges, and the statistical study of the arc transition revealed differences from other refractory target materials. The early stage of cathodic spot formation, observed as bright dots, will be presented and analyzed within the known "ecton" and "vaporization" models for spot formation. This experimental study highlights the role of luminous spot formation prior to arc transition, with possible optimization on the stability of magnetron discharges.