Progress on a multi-beam klystron for accelerator applications

Summary form only given. The multi-beam klystron (MBK) enjoys high efficiency, a consequence of the low perveance of the individual beamlets, while operating at a low beam voltage due to the high total perveance. The plasma wavelength is less than that of a conventional single beam klystron, allowing a significant reduction in the length of the device. MBKs are, therefore, especially attractive in lower frequency accelerator applications. The L6102-50 MBK, currently being developed at L-3 Communications Electron Devices, is designed to the DESY TESLA (Tera electron volt Energy Superconducting Linear Accelerator) specification, which calls for a 10 MW peak, 150 kW average power MBK at 1300 MHz. The klystron employs ten beams and a toroidal (i.e. ring resonator) cavity operating in the fundamental mode. This spaces the beams far apart to allow for a cathode size that reduces loading to under 2 A/cm/sup 2/. Models of the input cavity, the RF gain cavities, and the output cavity have been built and cold tested. Power is fed coaxially to the input cavity and extracted from the output cavity by two horizontally opposed waveguide outputs. All assemblies exhibit excellent agreement between measurement and modeling, with the frequencies, external Q-factors and R/Qs all very close to the design values. Current effort is concentrated on the electron beam optics. MICHELLE, NRL's 3D beam code, is being used. A beam tester is planned for 2004.