Research Topics

For the past three decades, Prof. Kwo-Ray Chu (the academician of Taiwan, National Taiwan University) and Prof. Tsun-Hsu Chang (National Tsing-Hua University) have dedicated to developing millimeter-wave to THz-wave high-power source based on gyrotron systems. Gyrotron is a vacuum electronic device, which is able to generate high-power radiations if gyrating beam and circularly-polarized wave can coherently interact with each other. Traditionally, gyrotrons were operated in TE modes of circular waveguides because of their simpler electric-field polarizations and weak bunching competition at near-cutoff operation. Since 2012, I started to help Prof. Tsun-Hsu Chang to investigate the TM-mode gyrotron. During 2012-2014, we completed the linear analysis of TM-mode gyrotron and discovered that TM modes are more suitable for backward-wave operation. This work has been published in “Physics of Plasma” (Phys. Plasma 24, 023302 (2017)). Extending from the linear analysis, in 2014-2016, we further analyzed the underlying bunching mechanisms and found that the azimuthal and axial bunching for the TM-mode backward wave will cooperate with each other instead of competition. This explains why the TM modes are more suitable for backward-wave operation that we discovered several years ago. With a simple confirmation by nonlinear but yet non-self-consistent simulation of a closed cavity, those discoveries have been published in “Physics of Plasma” (Phys. Plasma 24, 122109 (2017)). Around 2018-2019, the preliminary period of my postdoc career, we completed the analysis of starting behaviors of TM modes based on small-signal approximation. After solving the coupled Maxwell’s equations and relativistic Vlasov equation, we obtain the semi-analytical form of TM-mode starting current. These results were subsequently published in “Physics of Plasma” (Phys. Plasma 27, 022113 (2020)). On the parallel front, Prof. Chang and I also dedicated to studying the nonlinear and self-consistent analysis of TM-mode gyrotron. With 5-year effort, in 2021, we successfully obtained the formula for particle tracing and made complete analyses of the behaviors under beam current, voltage, velocity ratio and velocity spread tuning. This work has been recently published in “Physical Review E” (Phys. Rev. E 104, 065205 (2021)). In the future, we will focus on the experimental demonstration or time-dependent simulation of compact and low-voltage TM-mode gyrotron systems.