Efficiency improvement by a beam filtering ring in a relativistic backward wave oscillator at low magnetic field

Abstract

This paper presents a design method of the relativistic backward wave oscillator at low magnetic field, which can improve the efficiency by 29% in the particle in cell simulation. The core of this method is to introduce a beam filtering ring. The beam filtering ring takes the characteristic of the radial position change as the electron oscillates. The structure manipulates the axial current, so that a large proportion of the electrons expected to be in the accelerated phase in the slow-wave structure is absorbed by the structure. It greatly enhances the bunching of the beam in the RF field and improves the beam-wave conversion efficiency significantly. The particle in cell simulation results reveal that at a permanent magnet with a magnetic induction intensity of 0.68 T, the output microwave power of the relativistic backward wave oscillator with a beam filtering ring is 5.9 GW, and the conversion efficiency can be up to 54% when the diode voltage is 890 kV and the beam current is 12.2 kA.