Technological studies of high mission current density cathodes

Impregnated cathodes and encapsulated heaters show no change in their initial values up to 30,000 hr life if operating conditions are suitably adjusted. Small caps of ruby, sapphire, or quartz, as well as heater encapsulation, warrant good insulation between heater and cathode up to 10,000 hr, during the operation of a 1.5 mm diameter impregnated cathode. A 2 sec heat-up-time directly heated impregnated cathode was manufactured. The operating temperature of the lanthanum hexaboride cathode was found to be too high for general use. Cold electron emitters, especially external field emitters and negative electron affinity emitters, can be applied only in limited cases on account of their strong dependence on vacuum quality and their small emitting surfaces.