The Effect of Electrode Temperature on Vacuum Electrical Breakdown between Plane-Parallel Copper Electrodes

Abstract

Combined measurements of current‐voltage, prebreakdown characteristics, and breakdown voltage have been made for plane‐parallel, copper electrodes in ultrahigh vacuum as a function of both cathode initial temperature and anode initial temperature. These measurements have been carried out for an electrode separation of 0.1 cm over the temperature range from 313° to 913°K. From the experimental data the temperatures of the hottest point of the cathode surface, (T_C)_s, and of the anode surface, (T_A)_s, at breakdown have been determined as a function of electrode initial temperature. Over the whole range of the investigation it is found that (T_A)_s is greater than (T_C)_s. Moreover, the calculated values of (T_A)_s at breakdown are essentially independent of anode initial temperature and have a mean value of (1100±150)°K. In contrast, the values of (T_C)_s at breakdown increase with increasing values of cathode initial temperature. The results suggest that a thermal instability of a point on the anode surface leads to breakdown. A model for the breakdown mechanism is presented in terms of electron avalanche amplification of current in copper vapor. The vapor is generated by the detachment of an anode macroparticle and its subsequent evaporation during its transit to the cathode. The prebreakdown current plays an important role in the breakdown mechanism since it causes the initial thermal instability at the anode surface and, in addition, provides the necessary source of bombardment for evaporating the macroparticle.