@article {16209,
	title = {The design of a multi-harmonic step-tunable gyrotron},
	journal = {Physics of Plasmas },
	volume = {24},
	year = {2017},
	pages = {033101},
	abstract = {The\&nbsp;theoretical\&nbsp;study of a step-tunable\&nbsp;gyrotron\&nbsp;controlled\&nbsp;by successive excitation of multi-harmonic modes is presented in this paper. An axis-encircling\&nbsp;electron beam\&nbsp;is employed to eliminate the harmonic mode competition. Physics images are depicted to elaborate the multi-harmonic interaction mechanism in determining the operating parameters at which arbitrary harmonic tuning can be realized by\&nbsp;magnetic field\&nbsp;sweeping to achieve\&nbsp;controlled\&nbsp;multiband frequencies{\textquoteright} radiation. An important principle is revealed that a weak coupling coefficient under a high-harmonic interaction can be compensated by a high\&nbsp;Q-factor. To some extent, the complementation between the high Q-factor and weak coupling coefficient makes the high-harmonic mode potential to achieve high efficiency. Based on a previous optimized\&nbsp;magnetic cusp\&nbsp;gun, the multi-harmonic step-tunable\&nbsp;gyrotron\&nbsp;is feasible by using harmonic tuning of first-to-fourth harmonic modes. Multimode simulation shows that the multi-harmonic\&nbsp;gyrotron\&nbsp;can operate on the 34 GHz first-harmonic TE11\&nbsp;mode, 54 GHz second-harmonic TE21\&nbsp;mode, 74 GHz third-harmonic TE31\&nbsp;mode, and 94 GHz fourth-harmonic TE41\&nbsp;mode, corresponding to peak efficiencies of 28.6\%, 35.7\%, 17.1\%, and 11.4\%, respectively. The multi-harmonic step-tunable\&nbsp;gyrotron\&nbsp;provides new possibilities in millimeter{\textendash}terahertz source development especially for advanced terahertz applications.},
	url = {http://aip.scitation.org/doi/abs/10.1063/1.4977452},
	author = {Xiang-Bo Qi and Chao-Hai Du and Juan-Feng Zhu and Shi Pan and Pu-Kun Liu}
}
