A diode-type electron gun was used to investigate the dc emittion characteristics of a single-crystal LaB6 thermionic cathode. The emitting area was planar and of 2mm-diameter; achieving transmitted currents of up to 175mA and a current density of 5.6A/cm2. Comparing the measured current with Longo-equation fitting was more accurate than using other methods. When the vacuum was below 7 x 10-4Pa, the current density apparently decreased. The C and O in the surface of the emitter could increase the work function. Aggregation and diffusion of LaB6 to pyrolytic graphite made the resistance of the heater lower. Experimental results showed that the dc emitting current density was lower than pulse emission due to the finite diffusion velocity of La and the surface adsorption of remainder-gas.

DC Emitting Characteristics of Single Crystal LaB6 Thermionic Cathode. Wang, H.B., Xu, Z., Lu, H.P., Deng, R.P., Yang, X., Gan, K.Y., Jin, X., Li, M., Liu, X.S.: High Power Laser and Particle Beams, 2005, 17[6], 930-4