Dual-Band Terahertz Harmonic Gyrotron Driven by Axis-Encircling Electron Beam

Gyrotron driven by the axis-encircling electron beam is a pathway for generating frequency-tunable terahertz radiation on multiple harmonics. In this article, a large-orbit gyrotron (LOG) is designed, manufactured, and experimentally investigated. A magnetic cusp gun (MCG), demonstrating high robustness over a broad range of magnetic fields, has been developed to generate an axis-encircling electron beam with a constant pitch factor of 1.5 and a velocity spread of less than 2%. As the magnetic field strength adjusted at the operating voltage/current of 45 kV/0.7 A, the gyrotron is demonstrated to stably operate at the fundamental harmonic TE12 mode and the second harmonic TE24 mode, at the respective dual bands. The fundamental harmonic oscillation can achieve a wideband continuous frequency tuning range of 5.27 GHz around 160 GHz, with a maximum power of 7.42 kW, corresponding to a working efficiency of 23.5%, and the second harmonic operation can obtain a maximum power of 2.9 kW and an efficiency of 9.2%, with a continuous frequency tuning range of 1 GHz near 391 GHz. The quantitative agreement between experimental results and theoretical calculations indicates the reliability and correctness of the implemented gyrotron system, promising in achieving multiband oscillations at various cyclotron harmonics.