HEAT FLUXES DURING THE DEVELOPMENT OF A HOT ANODE VACUUM ARC

摘要

Heat transfer to a thermally isolated graphite anode in a long duration vacuum are was investigated. The anode bulk temperature was measured as a function of time using two high-temperature thermocouples. The anode surface temperature was optically determined. The visual image of the are was detected with the same optical system. A surface temperature of 2300 K was obtained in a 340 A are. A one-dimensional nonlinear heat flow model for the anode was developed. A solution was obtained using a dynamic numerical method and the time-dependent effective anode potential (defined as the ratio between the input power to the anode and the are current) was determined to decrease from a value of 10, 12 V at t = 0 to approximately 6.3 V at steady state observed for t greater than or equal to 100, 60 s, for are currents of 175 and 340 A respectively. Input power to the anode decreased on a timescale approximately coinciding with the appearance of an anodic plume which developed during the arcing. The effective potential of the water-cooled copper cathode (defined as the ratio between the net input power to the cathode and the are current) was determined to rise from 6.6 V near the beginning of the are to 7.2 V during steady state. The total are voltage, measured between the electrodes, increased from a value of approximately 21 V to a steady state value of 24, 26 V for are currents of 175 and 340 A respectively. [References: 14]