Theoretical and Experimental Studies of Oversized Ka-Band Surface-Wave Oscillators Based on 2D Periodical Corrugated Structures

Abstract

Based on the quasi-optical approach and direct PIC simulations, we study the dynamics of oversized relativistic Cherenkov-type surface-wave oscillators (SWO) with 2D periodical corrugated structures of cylindrical geometry. Such corrugation allows for a significant rarefication of the spectrum of modes with different azimuthal indices. As a result, selective excitation of a mode with a given azimuthal index is possible. Azimuthal index of the generated mode depends on the voltage rise time. For short (nanosecond scale) rise time, generation at the azimuthally symmetric mode can be realized. For longer (several hundred nanoseconds to microseconds) values of rise time, the modes with high azimuthal indices would be excited. These conclusions are supported by the experiments where Ka-band SWO with 2D corrugated structure was realized based on the thermionic-emission accelerator SATURN 300 keV / 100 A / 4 µs. In this SWO-type oscillator having an oversize factor (perimeter to wavelength ratio) of about 16, a stable narrowband generation with an output power of 2 – 2.5 MW was obtained at the frequency of 32.5 GHz corresponding to the mode with azimuthal index of $m$ = 3. The project of Ka-band sub-GW power SWO operating at the azimuthally symmetric mode is under development currently at IAP RAS based on the high current explosive-emission accelerator SINUS-6 500 keV / 4 kA / 20 ns.