Non-Adiabatic Electron Gun for Frequency-Tunable Gyrotrons

Cheng-Hung Tsai^1*, Toshitaka Idehara², Yuusuke Yamaguchi², Tsun-Hsu Chang¹

¹Department of Physics, National Tsing Hua University, Hsinchu, Taiwan
²Research Center for Development of Far-Infrared Region, Fukui University, Fukui, Japan

* Presenter:Cheng-Hung Tsai, email:arthur770410@gmail.com

We propose a non-adiabatic electron gun with high beam quality over a wide working range of magnetic field for developing 203 GHz frequency-tunable gyrotrons. The diode-type electron gun features a highly tilted emitter surface and a central aperture on the cathode. Emitter with nearly planar surface can inherently produce a laminar flow to suppress the velocity spread. Meanwhile, the central aperture helps to distribute electric field well along the beam trajectory to diminish the velocity spread due to electric field fluctuations. Our simulation shows a velocity ratio of 1.5 and spread of 6% from both EGUN code and CST Particle Studio. The beam quality is adjustable over a broad magnetic field of 7.4-8.0 T and a wide beam voltage of 12-22 kV. By applying the beam properties into the tapered cavity structure, simulations show a peak efficiency about 30% with 3dB tuning bandwidth around 8GHz, which suggests that the non-adiabatic electron gun is a promising candidate for continuously frequency-tunable gyrotrons.

Keywords: Gyrotrons, Electron beams, Cathodes