W-band gyro-devices using helically corrugated waveguide and cusp gun: design, simulation and experiment

Abstract

This paper presents the design and simulation of W-band Gyro-devices using helically corrugated waveguides as the beam-wave interaction region and a cusp gun as the electron beam source. The electron beam system and the beam-wave interaction were optimized through numerical simulations by using a particle-in-cell (PIC) code MAGIC to predict (calculate) the output power and frequency bandwidth. The beam cross sectional measurement using a scintillator plate confirmed that an axis encircling electron beam was achieved with the designed beam parameters of current 1.5 A and energy 40 keV. The W-band helically corrugated interaction region for the gyrotron backward wave oscillator (Gyro-BWO) was manufactured with a dispersion from 80 GHz to 110 GHz measured using a vector network analyser which was found to be in good agreement with simulations and theory. The Gyro-BWO achieved frequency-tuneable operation by adjusting the magnetic field in the interaction cavity. A -3 dB bandwidth of ~84-104 GHz and output power ~10 kW were simulated using the electron beam from the cusp gun. The gyrotron travelling wave amplifier (Gyro-TWA) is designed to have a -3 dB frequency bandwidth of 90-100 GHz, output power of 10 kW and saturated amplification gain of 40 dB.