Power-bandwidth extension in a high power, s-band multiple-beam klystron

Summary form only given. We present the design of a broadband multiple-beam klystron (MBK) capable of generating >700 kW of peak RF power with a 3-dB instantaneous bandwidth of >11% at a center frequency of ~3.3 GHz. The MBK will operate in the TM₀₁ fundamental-mode and is designed to be powered by an 18-beam, 42 kV, 41.6 A electron gun that is currently in fabrication. The gun employs a concentric beam-packing topology of 6 inner and 12 outer beamlets, each with an emitter current density of ~11 A/cm². The electrodynamic circuit is comprised of six cavities with an overall length of 22 cm. Three of the six cavities are of a two-gap design, with inherently higher R/Q's as compared to single-gap cavities, thus enabling broader bandwidth operation and higher power and gain in a shorter interaction length. We will describe our design methodology, including the development of analytic design aids, discuss design trade-offs, and present final circuit parameters along with the results of 3-D particle-in-cell simulations of realistic circuit topologies