Effect of the Erosion of Collector Surface on the Operation of a Pulse-Periodic Plasma Relativistic Microwave Generator

The pulse-periodic operation regime of a plasma relativistic microwave generator is considered. The reasons for the increase of average frequency of the output microwave radiation in a pulse train created in the same conditions of initial plasma generation are analyzed. The effect of solid body erosion that occurs due to the interaction of the relativistic electron beam with the collector surface on the output microwave radiation is studied. The analysis of experimental data is accompanied by numerical simulations by the electromagnetic PIC code KARAT. It is shown that increasing the amount of mater extracted from the surface of the collector during erosion leads not only to an increase of the plasma density, but it can also lead to qualitative changes of the parameters of the output radiation, which are caused by the change of microwave generation regime. In particular, the generation of an ion background that is inhomogeneous in the radial direction caused a change of conditions of plasma–beam interaction during the second half of the pulse and a change of the spectral density of radiation at the main frequency. Numerical simulations were used to demonstrate this for two different admixtures, iron and graphite.