An annular explosive cathode with a shielding ring for the X-band high-impedance relativistic klystron amplifier

Abstract High impedance (>1 kΩ) relativistic klystron amplifiers (RKAs) are able to avoid power capacity limitations with higher conversion efficiency, compared with low impedance RKAs. An annular explosive cathode is investigated to offer moderate density electron beams for an X-band high-impedance RKA. Instead of a traditional solid thermionic cathode applied to a high-impedance RKA, the annular explosive cathode is able to simplify and minimize its conventional electron optics system. Nevertheless, the impedance of explosive cathode is hardly to achieve as high as kΩ level. A shielding ring is introduced to realize the high impedance of 1.15 kΩ and reduce the surface electric field on unexpected explosive emission region. Analysis of the explosive cathode employed in the X-band high-impedance RKA are described. The fine performance of this RKA is demonstrated by 2.5-D particle-in-cell (PIC) simulations. The typical microwaves with a power of 100 MW are generated at a frequency of 11.424 GHz when the beam voltage and current are 527 kV and 457 A respectively, under a guiding magnetic field of 0.55 T. The corresponding power conversion efficiency and gain are as high as 42% and 50 dB.