DC emitting characteristics of single crystal LaB6 thermionic cathode

A diode- type electron gun is used to investigate the DC emitting characteristics of a single crystal LaB6 thermionic cathode. The emitting area is a planar 2 mm- diameter, achieving transmitted currents up to 175 mA and a current density of 5.6 A/cm2. Comparing the measured current with fit result by Longo equation, Longo equation fitting is more accurate than the other methods, and applicable for practical operation. The circumstance has an effect on the emitting ability of cathode, when the vacuum is below 7×10-4 Pa, the current density apparently decreases. The C and O in the surface of the emitter can increase the work function. Aggredation and diffusion of LaB6 to pyrolytic graphite make the resistance of heater lower. Experimental results show that DC emitting current density is lo