Surface changes in Fe-Cr-Ni alloy bombarded by relativistic pulsed electron beam and associated mechanism

This paper presents the surface structure changes of Fe-Cr-Ni alloy wires uses as anode grid of vircator during relativistic electron beam irradiation. It is observed that the anode materials are deposited on the cathode surface. The deposited anode materials are in fact new impurities, possibly lowering the uniformity of explosive electron emission of carbon fiber cathode. The results of alloy wires before and after the irradiation of pulsed electron beam are compared. The microprotrusions, with the height of 300-400 μm and width of 100 μm, distribute quasi-periodically on the surface of alloy wire. Further, the appearance of these microprotrusions decreased obviously the microwave power of vircator. The mechanism of generation of anode target microprotrusions is theoretically analyzed. The non-equilibrium between the electrical field pressure and electron beam pressure induces the appearance of microprotrusions on the anode surface. This brings insights in enhancing the property of microwave tubes.