On the Temperature of Cathode in Vacuum Arc

Abstract

Pyrometric and spectroscopic tests show that the metal cathode spot in a vacuum arc is not at an extremely high temperature. The temperature of a copper cathode is measured by an optical pyrometer and found to be about 3000°K in a 20 ampere arc. Spectroscopic examination of the cathode spot shows only a faint continuous spectrum indicating that the temperature of the cathode is not high. A temperature of the above magnitude is shown to be sufficient to give the rate of vaporization required to account for observed loss of cathode material under extreme assumptions. The results show that the high speed of the vapor stream issuing from the cathode region cannot be due to high temperature of the cathode itself.