Power And Frequency Measurements From A Uniform Backward Wave Oscillator As A Function Of Length

Abstract

The authors describe results from an experiment where the number of ripple periods in the slow wave structure of a backward wave oscillator (BWO) is increased. Both microwave power and frequency measurements are made for each shot. For a given cathode voltage and beam current, the microwave peak power and frequency are plotted as a function of BWO length. In previous investigations, the observation of two power maxima as a function of length was explained by the interaction of the electron beam with the forward traveling wave and reflections at the transition from the slow wave structure into the output waveguide. However, recent numerical calculations using the phase dynamics of electron beam and electromagnetic modes suggest that the power maxima are due to the phase relationship between the electron beam density wave and the backward wave. Experiments were performed on the Sinus-6, a relativistic electron beam accelerator. By adjusting the pressure in the Sinus-6 spark gap switch, cathode voltages between 400 kV to 650 kV can be obtained. The experiment was repeated for different sets of beam parameters. In all cases, the magnetic field used for beam transport was longer than the length of the slow wave structure. The experimentalmore » results are compared with phase model calculations and PIC code simulations using KARAT and TWOQUICK.« less