Sectioned Gyrotron Cavity Supporting a Complicated Axial Mode With Reduced Diffraction <i>Q</i>-Factor

In short-wavelength gyrotrons operating at high cyclotron harmonics, long cavities are required to provide the start of operating oscillations. In this situation, high diffraction Q-factors lead to a problem of a high share of ohmic losses. In this article, a cavity consisting of two sections separated by a short cutoff narrowing is proposed as a way to decrease the share of ohmic losses. As compared to the regular cavity of the same length, in the sectioned cavity, the operating wave has a shorter effective length of its field and, therefore, a lower diffraction Q-factor. In a definite range of parameters, this wave wins in a competition with another, parasitic axial mode, which has a relatively low starting current and starts first, but it is suppressed by the operating mode at the steady-state generation regime.