Design and preliminary experiment of a disk-beam relativistic klystron amplifier for Ku-band long-pulse high power microwave radiation

Spatial coherent combination of multiple high power microwave (HPM) sources is considered as a promising scheme to improve the equivalent radiation power of the HPM system dramatically. Relativistic klystron amplifier (RKA) is one of the most suitable sources for the coherent power combination owing to its specific capabilities of stable microwave frequency and controllable phase. However, the RKAs operating at high frequency-band are severely limited by the problems of the intense space-charge effect and radio frequency breakdown. The radial-line HPM sources driven by the disk-shape electron beam may provide the potential to alleviate this issue due to its attractive features of the weak space-charge effect, the high power handling capacity, and the strong electron collection ability. In this paper, a disk-beam relativistic klystron amplifier (DB-RKA) is proposed and physically designed aiming to generate long-pulse HPM radiation at Ku-band. The physical idea, design principles, and simulation results are presented in detail. In a preliminary experiment, the disk-shape intense electron beam is well focused with an axial-width of 1.2mm by an improved magnetic-excited method. Furthermore, the DB-RKA is demonstrated to be capable of generating Ku-band HPMs typically with peak power of 320MW, pulse duration of 100ns, and gain of 42dB.