Spatial-temporal hysteresis effects in an intense electron beam

An electron gun with large compression of a thin annular beam for generation of high-power microwaves and IR radiation has been designed. Computer simulations of beam formation in the gun show some hysteresis effects: a beam with different current can exist in the same external conditions. At the upper (metastable) part of a hysteresis curve the beam current exceeds Child-Langmuir current. Experimental observation of these metastable states is possible if one has the possibility for fast control of emitted current, which is the case for photoemission cathode. The results of computer simulation are presented and physics reasons of such behaviour are discussed.