On reduction of transient process duration in a relativistic Cherenkov microwave oscillator without a guiding magnetic field

Coupling impedance $Z_0$ of a continuous relativistic electron beam with the fundamental harmonic of the TM$_{01}$ wave slowed down to the speed of light in a slow-wave structure (SWS) based on a hollow corrugated waveguide is estimated analytically and using the program based on the scattering matrix method. It is shown that $Z_0$ in relativistic Cherenkov microwave oscillators without a guiding magnetic field realized in earlier experiments with the given type of interaction amounts to about 6–7 $\Omega$, which is several times higher than the coupled impedances averaged over the SWS cross section for -1 and +1 spatial harmonics of the operating wave and can be increased in future to values exceeding 10 $\Omega$ due to a decrease in the average SWS diameter in admissible limits. In numerical simulation using the KARAT code, the possibility of reduction of the time of stabilization of oscillations of the Cherenkov microwave oscillator without a guiding magnetic field by 1.5 times is demonstrated.