A Study of an Ultracompact High-Efficiency CSM MBK Using Hybrid-Modes Resonant Cavities

The multibeam klystron (MBK) faces the challenge of miniaturization together with stringent requirements for high power and high efficiency (HE) in L-band and below frequency regimes. Inspired by the core stabilization method (CSM), this article proposes three types of hybrid-modes resonant cavities, which can operate simultaneously in two harmonic modes. The large-signal simulation and 3-D particle-in-cell (PIC) simulation results demonstrate that this novel CSM MBK equipped with two hybrid-modes resonant cavities, operating at both fundamental and second harmonics, could provide up to 11.5-MW output power with 65.9% electronic efficiency at a total circuit length of 592 mm. This L-band MBK is launched with six beamlets, of which the beam voltage is 110 kV and the total current is 168 A. Moreover, compared with the MBKs designed by the traditional approach with only fundamental cavities or the CSM approach with individual harmonic cavities, the new hybrid HE klystron proposal exhibits not only decent efficiency performance but also, more importantly, ultracompact dimensions, where the circuit length is significantly shortened by about 45% and 35%, respectively.