Lewis R. Koller

Cathode Sputtering in Arc Discharges

A method is described for measuring the number of atoms of thorium sputtered from tungsten by positive ions of various velocities in the positive column of an arc discharge. The threshold for mercury ions is 35 volts. The number of atoms sputtered per positive ion in mercury vapor increases with increase in filament temperature and with decrease in arc current. The effectiveness of ions in sputtering thorium from tungsten is in the order neon, argon, mercury. Measurements of emission from a probe permit observations of the rate of loss of barium from an oxide coated cathode. The threshold for sputtering from a cold oxide coated filament by neon ions is approximately 45 volts. The material sputtered is not electrically charged. There is a difference in nature between the material evaporated and sputtered from an oxide coated cathode. The threshold for sputtering of barium from tungsten is 14 volts for argon ions and approximately the same for neon. The arc current to a coated cathode reduces the rate of lo...