摘要
This study investigates the interaction between the relativistic electrons and the waves in cavities with fixed field profiles. Both the transverse electric (TE) and the transverse magnetic (TM) cavity modes are examined, including three first-axial modes, TE , TM , and TM , and two zero-axial modes, TM and TM . The first-axial modes have the same resonant frequency, so a direct comparison can be made. By sweeping the electron pitch factor (α) and the electron transit angle (Θ), the optimal converting efficiency of TM modes occurs at α = 1.5 and Θ = 1.5π, unlike the TE mode of α = 2.0 and Θ = 1.0π. The converting efficiencies of both the first-axial TM modes are much lower than that of TE mode. The starting currents of TM and TM modes are four times higher than that of TE mode, indicating that these two TM modes are very difficult to oscillate. This evidences that under the traditional operating conditions, the TM-mode gyrotrons are insignificant. However, the two unique, zero-axial TM modes have relatively high converting efficiency. The highest converting efficiency of TM is 27.4%, the same value as that of TE mode. The starting currents of TM mode and TE mode are at the same level. The results suggest that some TM-mode gyrotron oscillators are feasible and deserve further theoretical and experimental studies.