Observation of Cathode-Spot Phenomena at the Surface of a Dielectric Powder-Covered Electrode in the Presence of a Background Plasma and Applied Magnetic Field

An electrode containing a layer of micrometer-sized ceramic powder was exposed to a low-pressure background argon plasma. Negative biasing of the electrode resulted in the formation of localized arcs which manifested attributes similar to that observed in vacuum cathode-spot discharges. The arcing action on the electrode in the presence of an applied magnetic field ejected particles and metal vapor, eventually etching repeatable tracks into the electrode surface. The regular tracks left by the action of the cathode spots on the electrode surface suggest J times B effects. The cathode-spot waveforms and erosion tracks with and without an applied magnetic field were documented using a fast frame rate camera and oscilloscope.