On the possibility to realize the efficient relativistic Čerenkov microwave generator without an external guiding magnetic field

Abstract

We consider the preconditions for efficient operation of the relativistic Cerenkov microwave generator in the absence of an external guiding magnetic field. The analytical expression for the length of propagation of a solid cylindrical electron beam along the drift tube is obtained in the framework of the paraxial approximation. The influence of preliminary modulation of the electron beam on the starting current of the generator and its linear efficiency is analyzed. We calculated the geometry of a relativistic Cerenkov microwave generator with an efficiency of about 30%, in which the solid cylindrical electron beam propagates over a short resonance decelerating system (with the length L ≈ 3λ, where λ is the radiation wavelength) in the absence of an external magnetic field. In experiments, the efficiency of power conversion from the high-current electron beam into the electromagnetic radiation of the E01 mode reached 8%, approximately (relative to the total current of the vacuum diode), for a power of 1.2 ± 0.3 GW and a generation frequency of 4.06 GHz.