Starting behaviors of the TM-mode gyrotrons
Hsin Yu Yao1*, Chih Chieh Chen1, Tsun Hsu Chang1
1Physics, National Tsing Hua University, Hsinchu, Taiwan
* Presenter:Hsin Yu Yao,
A clear derivation of the TM-mode starting currents based on the Laplace method and the numerical method is demonstrated. Calculated results of these two approaches perfectly match with each other for a uniform structure, while the numerical method is advantageous for practical non-uniform structures. The beam-wave coupling strength of the TM-mode gyrotron strongly correlates with its starting current. This unique feature can be used to suppress the competition from the TE modes. We found that the starting current of the TM11 gyrotron exhibits an additional operating condition at the low-beam voltage region that can facilitate the development of low-cost and tabletop gyrotron systems. The beam-voltage and magnetic-field tunings are investigated for an open-cavity structure with the numerical method. Interestingly, the TM11 gyrotron as well as the TE01 gyrotron exhibit a similar starting behavior, which warrants the potential applications of the TM-mode gyrotrons.

Keywords: starting current, TM-mode gyrotron, modal coupling strength, mode competition