Indirectly heated cathode with long life especially for X=ray tubes for examination of materials

摘要

The cathode has an electron beam emission surface which is heated by heater (4) arranged at a distance behind the emission surface. Thermal electrons from the heater are accelerated, through an electric field to the reverse of the emission surface. The heater (4) is formed as a flat round beam emitter. This is operated with lower temperature and higher acceleration voltage than the emission surface. The heater preferably has a flat tungsten coil. The heater may be a directly heated surface emitter with two connection tabs arranged on the circumference to feed the heating current.