Experimental investigation of current fluctuation at a short emitter to anode distance

It was experimentally observed that the number of spike-like noise was increased as the anode approached the emitter, under bad vacuum conditions of 10−6 Torr. The duration of the stable emission also decreased upon approaching the anode to the emitter. It is numerically solved that the number of generated gas molecules and ions by electron-stimulated desorption on the anode surface come to the emitter surface. Under UHV (ultra-high vacuum), the number was not much affected by the distance. On the other hand, under bad vacuum conditions, the number was increased largely as the anode approached the emitter. It suggests that the gas molecules and/or ions generated at the anode surface hitting the emitting area on the emitter is affected by the emitter to anode distance.