Development of a CUSP-Type Electron Gun for a W-Band Helical Gyro-TWT

To drive a broadband gyro-TWT with a helically corrugated interaction region, a high-quality axis-encircling electron beam is required. In this publication, a CUSP-type electron gun, capable of generating such a beam, is developed for a 94 GHz helical gyro-TWT. The design was optimized using the electron-beam-optics code ESRAY [1]. The final electron gun is optimized for the generation of an electron beam with a 50 kV beam voltage, 1.5 A current, and a pitch factor of $\alpha=1.0$ with an RMS spread as low as 3.49 %. Additionally, tolerance studies, including the influence of deviations in the emitter position and the surface roughness of the emitter, are performed.