Model of emitting sites and erosion on nonrefractory arc cathodes with relatively thick oxide films

A model is proposed for the mechanisms by which multiple emitting sites are formed and material is lost from a nonrefractory arc cathode with an oxide layer more than about 10¿8 m thick, when an arc is rotated magnetically over its surface for long times. Using measured copper cathode erosion rates and scanning-electron-microscope photographs of the size and number of craters on cathode arcing surfaces, results have been obtained which seem to support the model. Average lifetimes of emitting sites have been estimated to be considerably greater than those on cathodes with very thin oxide films. The model suggests that it is important to keep the oxide layer from becoming too thick, to obtain low cathod erosion rates.