Design and Operation of an S-Band 6% Bandwidth Multiple-Beam Klystron

We describe the design and characterization of a broadband eight-beam, fundamental-mode multiple-beam klystron (MBK), and present preliminary experimental hot-test results. The MBK is designed to have a 3-dB instantaneous bandwidth of-6% with a center frequency of ~3.2 GHz and uses an existing eight-beam electron gun that operates at a nominal cathode voltage of 45 kV and a total current of 32 A1. The electrodynamic circuit is comprised of a two-gap input cavity, three idler cavities (the first of which is a two-gap cavity), and a two-gap output cavity". The total length of the electrodynamic circuit is ~22 cm. All of the multi-gap cavities are designed to operate in the pi-mode. The individual cavity-designs were optimized with the aid of 3D electromagnetic modeling tools and the designs and final fabricated hardware were validated with extensive cold-testing. We will present comparisons of the measured cavitv parameters (frequency, Q, R/0) with 3D electromagnetic simulations. The predicted peak output power over the band is about 600 kW with a corresponding efficiency of 42% and a gain of ~33 dB. The predicted 1-dB and 3-dB instantaneous band-widths of the device are 5.2% and 6.7%, respectively. The MBK is being fabricated by CPI and is expected to be delivered to NRL in early 2007. We will present preliminary experimental results with this device.