ABSTRACT
Primary electrons delivered by cathodes of various design play a vital role in many ion sources. This chapter summarizes some data on cathode design and material. Metal cathodes operate at high temperatures to imply high radiation heat for the surrounding walls with the need for intensive cooling. Metal cathodes are easily corroded by oxygen and other reactive gases. Lanthanum hexaboride is an excellent electron emitter at medium temperatures. LaB6 cathodes are stable against ion bombardment and well suited for ion sources. Because of more difficult preparation techniques LaB6 cathodes are less used than metal cathodes despite their excellent emission data. Liquid-metal cathodes are generally known as mercury pool cathodes and are rarely used in ion sources. The metal vapor vacuum arc cathode is, in principle, a liquid-metal cathode. Hollow cathodes are usually cold cathodes, which have much higher electron emissions than planar cathodes. Hollow cathodes may have coated or heated walls to increase electron emission.
