Anode surface radiance from microsecond vacuum arcs

Abstract

Measurements of anode surface radiance as a function of time for microsecond-duration vacuum arcs have been performed using an infrared-sensitive solid-state detector. Anode surface temperatures have been inferred from the measured radiance values using information concerning the surface spectral emittance. Particular attention has been given to the measurement of anode spot temperatures as a function of time. The anode materials investigated are Al, Cu, and Kovar. In addition, surface temperatures due to plasma heating of Al2O3 (alumina) and BeO (beryllia) ceramics surrounding the active anode area have been determined. Values of the average anode current density ranged from 6×103 to 5×104 A/cm2, with arc current pulse lengths of 1–12 μsec. Anode spot temperatures between 2600 and 3300°C for Cu, and between 2000 and 2400°C for Al were observed. The maximum surface temperatures of the ceramic insulators were between 2900 and 3500°C for Al2O3 and between 2000 and 2300°C for BeO. Calculations based on an integral equation solution to the heat-flow equation suggest that the input power density to the surface falls between 106 and 107 W/cm2 for Al, Cu, Al2O3, and BeO. Based on these values, estimates of the anode spot current density for Al and Cu fall between 105 and 106 A/cm2.