Output microwave characteristics of a Ka-band relativistic klystron amplifier with spatially nonuniform multibeam electron emission

Abstract

The effects of spatial nonuniformity of electron multibeam emission on the output characteristics of a coaxial multibeam Ka-band relativistic klystron amplifier (RKA) are investigated using particle-in-cell simulations. The spatial nonuniformity is simulated using four different electron multibeam emission models, with (1) a continuous cathode non-emission area, (2) discontinuous cathode emission areas, (3) discontinuous cathode emission areas with different electron emission current densities, and (4) cathode emission areas with different and time-varying electron emission current densities. The simulation results with the first model show that the output microwave power of the RKA decreases as the continuous non-emission area increases, but that size of the continuous non-emission area has little effect on the frequency and pulse width of the RKA. The results with the second model show that the more uniform the electron current density in the discontinuous emission areas, the greater the output microwave power. The results with the third model show that the more uniform the distribution of the Z component of the induced electromagnetic field in the discontinuous emission areas, the greater the output microwave power, and also that the output microwave power increases as this Z component increases. The results with the fourth model show that fluctuations in the electron current density in the discontinuous emission areas in the steady-state phase of RKA operation cause fluctuations in both microwave frequency and output microwave power and that these fluctuations increase as the fluctuations in electron current density become stronger and as they become more rapid.