The stationary vacuum arc on non-thermionic hot cathode

Experimental study of vacuum arc with distributed spot on plumbum cathode at temperatures 1.25-1.45 kK has been presented. At these conditions current density of thermionic emission from cathode was less than 1 μA/cm², while the mean current density on the cathode was about 10 A/cm². Plumbum was placed in heat-insulated crucible (cathode) with external diameter 25 mm. Electron-beam heater was situated under the crucible. Arc current was changed in the range 20-70 A, arc voltage was about 15 V. The studied arc is characterized by the absence of the random voltage fluctuations; the micro particles of cathode erosion products were observed only in transition regimes. Spectral data of plasma radiation and values of the heat flow from plasma to cathode were obtained. It has been experimentally established that the evaporation rate in arc approximately two times less than without discharge. The average charge of plumbum particles in the cathode jet was in range 0.2-0.3e. Comparison of the characteristics of studied discharge on thermionic gadolinium cathode and non-thermionic cathodes was fulfilled. One can assume that ions provide the charge transfer on the cathode in the studied discharge. (paper)