Influence of RF Breakdown Plasma on Dispersion Relation of High Frequency Structures and Characteristics of Generated Microwave in Relativistic Backward Wave Oscillators

Abstract

High power, long pulse and high repetition rate are the developing direction of high power microwave (HPM) system. The relativistic backward wave oscillator (RBWO) is considered to be a promising device for the future application among many kinds of microwave sources due to its potential of large power capacity, high beam-wave interaction efficiency and good operation stability. With decades of development, the HPM system nearly operates at its limiting parameters of all aspects (cathode, high frequency structure, electron beam collector and microwave output window). Among these limitation factors, The Radio Frequency breakdown (RF breakdown) of the slow wave structures (SWSs), which will lead to the generation of the RF breakdown plasma, is an important cause for pulse shortening and power decaying in RBWOs.Although many researchers have performed some valuable studies about this issue, further researches of the influence mechanism of RF breakdown on the microwave generation are still needed.In this paper, we consider the RF breakdown plasma will influence the microwave generation in two ways. One is the plasma brought by RF breakdown will influence the quality of electron beam and absorb microwave energy. The other is the RF breakdown plasma will change the electrodynamic property of the SWSs in some degree by influencing the dispersion relation, which leads to the microwave sources operate at an improper condition. Theoretical analysis, numerical calculation and particle in cell (PIC) simulations are conducted to verify our conclusion. The results obtained are helpful in explaining the RF breakdown phenomenon physically and can provide some design guidance.