Contents I. Introduction
Cathode-Spot phenomena have been studied for many years. Interest in these phenomena stems from the associated technological applications ranging from high-voltage interrupters to welding arcs. Current vacuum cathode-spot formation theories point to localized heating of microscopic protrusions driven by either intense field emission or localized high-current ion bombardment of the protrusion resulting in thermal electron emission. The rapid heating at the protrusion gives rise to the formation of a very localized arc known as a cathode spot. The spot “burns” in the vapor produced at the protrusion, which is consumed in the process [1]–[10]. Cathode spots themselves are fascinating states of matter with plasma densities reported as high as , electron temperatures on the order of a few electron volts, and flow speeds in excess of [5], [6]. These conditions make cathode-spot flows attractive candidates for the acceleration of nano-to-micrometer-sized particles [11]. Cathode-spot acceleration of non-electrode-derived particles has also been demonstrated [12]. As part of a continuing investigation of such acceleration, cathode spot-like arc formation and behavior on a ceramic-powder-covered negatively biased electrode in the presence of a background plasma and an applied magnetic field is studied. In this case, the phenomena observed, strictly speaking, are distinct from purely vacuum arc phenomena, owing to the presence of gas at appreciable pressures (mtorr) and background plasma, although many similarities exist as discussed. The goal of this paper is to present the observed cathode-spot behavior under these unique conditions and to document the erosion patterns and associated cathode-spot waveforms. Electrode wear patterns observed are compared with the calculated vector field based on arc current and surface magnetic field data.
