Long pulse CsI impregnated field emission cathodes

Intense pulsed electron beams are produced by applying a voltage between an anode and a cathode in a vacuum diode. The average field can be as low as 10 kV/cm, depending on the cathode material. This field is much less than predicted by the Fowler–Nordheim equation for field emission. The source for the electrons is a plasma that forms on the cathode which has a zero or very low work function. This plasma propagates into the anode–cathode gap and as a result lowers the impedance and eventually shorts the diode. The impregnation of the cathode surface with CsI was found to delay the onset of the diode impedance collapse. The time behavior of the impedance of a diode driven by 400-kV, 1-μs pulse was investigated. Three cathode materials with and without CsI were evaluated.