Anode Temperature and Plasma Sheath Dynamics of High Current Vacuum Arc After Current Zero

Abstract

This paper addresses the behavior of a high-current vacuum arc after current zero (CZ). Langmuir probes operating in the electron saturation current mode are used to detect the time of arrival of the cathode sheath at the probe position. The probe current is measured just before and after the CZ followed by transient recovery voltage both with and without external axial magnetic field (AMF). For an AMF-stabilized arc, the plasma sheath expanded radially with respect to the electrode axis, whereas for an arc with no AMF, the sheath boundary expanded rather spherically away from the anode. The anode temperature immediately after the CZ is estimated using the optical pyrometry method. Thermal radiation of a hot sample is recorded using a HSFC four-channel high-speed camera. Each camera channel is equipped with an interference filter to record radiation at a particular wavelength (600, 700, 775, and 825 nm). The camera channels are preliminarily calibrated. The calibration sample is a molybdenum crucible with a known spectral emissivity.