Details

Autor(en) / Beteiligte

• Yang, Tien-Fu
• Yao, Hsin-Yu
• Chang, Chia-Chuan
• Du, Chao-Hai
• Zhang, Feng
• Chang, Tsun-Hsu

Titel

TE- and TM-Mode Competition in Subterahertz Gyrotron Using Axis-Encircling Electron Beam

Ist Teil von

• IEEE transactions on electron devices, 2024-01, Vol.71 (1), p.815-821

Ort / Verlag

New York: IEEE

Erscheinungsjahr

2024

Quelle

IEEE/IET Electronic Library

Beschreibungen/Notizen

• For a long time, most gyrotron oscillators have avoided using TM modes because of the concerns about strong bunching competition and relatively weak beam−wave coupling. However, this work demonstrates that an axis-encircling electron beam with high mode selectivity is adapted to preclude most parasitic modes and makes the TM12-mode oscillation in an open-cavity-type gyrotron system feasible. Considering the modes excited at the fundamental cyclotron harmonic, the TE12 mode remains to be the only competitor to the targeted TM12 mode; however, it will be effectively suppressed by the axial velocity spread. Operating with 70-kV beam voltage and 1-A beam current, the output power of the TM12 mode may reach the several-kilowatt level, verified by both nonlinear frequency-domain and time-domain simulations. Nonetheless, as the modes at high cyclotron harmonics are included, the second-harmonic TE24 mode and the third-harmonic TE36 mode would potentially hazard the proposed TM12-mode operation. Even so, the particle-in-cell (PIC) Computer Simulation Technology (CST) simulation results still show a tunable window of the TM12 mode, where all parasitic TE-mode oscillations are fully suppressed. This work manifests the importance of considering the competition from TM modes in the designs of gyrotron devices, especially for the cases using axis-encircling electron beams.