1.Guilin University of Electronic Technology;2.Research and Development Center,Dynex Semiconductor Ltd,Lincoln,LN LF,UK;3.School of Electronic Science and Engineering,University of Electronic Science and Technology of China,Chengdu;4.National Key Laboratory of Science and Technology on Vacuum Electronics Beijing Vacuum Electronics Research Institute
National Natural Science Foundation of China (62001131), Guangxi Natural Science Foundation Project (2019GXNSFBA245066), Guangxi Natural Science Foundation (AD19245042), the Dean Project of Guangxi Key Laboratory of Wireless Broadband Communication and Signal Processing Grant (GXKL06190102).
—The large-orbit gyrotrons (LOGs) in the THz range are attractive for the great potential of reducing the required external magnetic field by enabling the high-harmonics operation. In this paper, a LOG capable of operating from the 4th to the 9th harmonic is designed and investigated. With the assistance of the 3-D particle-in-cell simulation, the key features of the designed LOG, beam-wave interaction dynamics and high-harmonic operation regimes are studied. It is shown that by tuning the external magnetic field intensity, successive excitation of the oscillation at a number of neighboring harmonics can be achieved, corresponding to radiation frequencies between 240 GHz to 460 GHz with the maximum radiation power of 19 kW. Then, a detailed study of the competition among the 7th, 8th and 9th harmonics are conducted, providing an insight into the multi-modes, multi-harmonics behavior of the high-harmonic LOG. Following that, the methods to stabilize the beam-wave interaction and enable single mode operation at high harmonics are discussed. Additionally, the characterization of the ohmic loss power at different operation harmonics is conducted.