A compact coaxial relativistic klystron amplifier with three cascaded single-gap bunching cavities for efficient output

Abstract

A compact coaxial relativistic klystron amplifier (RKA) with three cascaded bunching cavities is investigated to obtain high efficiency output in this paper. When the injection power and drift tube length are both decreased for the compactness of the initial coaxial RKA, the conversion efficiency of this device decreases to only 20%, which is mainly due to the insufficient modulation of intense relativistic electron beam (IREB). To solve this issue, three cascaded bunching cavities are designed to strengthen the modulation of IREB, and each bunching cavity is designed to a non-uniform single-gap cavity with a high external quality factor. Moreover, a specific drift tube length is chosen for minimizing the TEM mode leakage between every two adjacent cavities. With these methods, the self-oscillation between input and three cascaded bunching cavities can be successfully suppressed without loading any reflectors. The proposed three cascaded single-gap bunching cavities are further examined in a Ku-band coaxial RKA, and the output efficiency of this device increases to 44%, which is more than twice that of the initial coaxial RKA. Furthermore, the injection power and axial length of the propagating IREB in the improved coaxial RKA are reduced to only 5 kW and 10 wavelengths, respectively.

Research on TEM mode feedback and distributed reflection for high-power output of a V-band transit-time oscillator under a low guiding magnetic field

“…In this RCTTO, a two-stage cascade buncher is adopted instead of the conventional single buncher 9,10 for the velocity modulation of IREB. Meanwhile, to enhance the gap voltage of the second buncher to strengthen the modulation of the IREB, a TEM mode positive feedback mechanism [11][12][13] has been introduced, which can also be used to reduce the drift length between the first and second buncher as much as possible so that improving compactness. Moreover, to improve the transmission stability of the electron beam, distributed reflection is also adopted in the RCTTO, which can better isolate the TEM modes compared to the conventional reflector.…”