High-Power High-Efficiency L-band Multiple-Beam Klystron Development at CPI
Communications and Power Industries, Inc., has designed and manufactured two versions of a 10-MW-peak high-efficiency multiple-beam klystron (MBK) operating at 1300 MHz. This type of klystron is favored for large particle accelerator projects such as the European X-ray Free-Electron Laser at the Deutsches Elektronen Synchrotron (DESY). Two klystrons have been made for DESY. The first-generation MBK was a vertically oriented prototype using a six-cavity design with higher order mode input and output cavities and conventional intermediate cavities. For cost and performance reasons, the second-generation MBK, designated VKL-8301B, utilized seven coaxial fundamental-mode cavities and is an “industrialized” horizontally oriented klystron. The klystron was designed and optimized using state-of-the-art multidimensional design codes to ensure that all performance requirements are exceeded. Agreement between the simulated and measured performances is good. The VKL-8301B prototype achieved a peak saturated RF output power of 10.4 MW and 67.8% efficiency. The data were measured at the full 1.5% duty and with 1.5-ms pulse width. The klystron satisfied all required operating conditions, including stable operation into an output mismatch of 1.2:1 voltage standing wave ratio at various phases. The prototype has been shipped to DESY and has been successfully tested by a customer.
Development of an S-Band High Average Power Multibeam Klystron With Bandwidth of 10%
An S-band high average power multibeam klystron (MBK) producing peak power of 500 kW and average power of 30 kW over 10% of relative simultaneous bandwidth has been designed and developed in Institute of Electronics, Chinese Academy of Sciences (IECAS). The biggest challenges were achieving over 10% relative simultaneous bandwidth performance with higher efficiency at the same time and focusing and transport of the intense electron beam because of the highest level average power in all types of MBKs in IECAS. Two prototypes were manufactured and both have been thoroughly tested. The fundamental mode was chosen for the RF interaction system, 24 beams are used to obtain a beam current of 50 A and the beam voltage is 29 kV. The efficiency is greater than 40% and the gain is greater than 37.5 dB over a relative simultaneous bandwidth of 10%. Both design considerations and experimental results have been addressed in this paper. The experimental results are close to design specifications.
A Second Long Pulse Modulator For TESLA Using IGBTs
A second and third modulator are being built at Fermilab to drive the klystrons for the TESLA Test Facility. These modulators are similar to one previously built at Fermilab. However, there are two differences. First, the new modulators are designed for a 10 MW multi-beam klystron under design by Thomson. Second, IGBT switches are being used in place of GTOs. The development of the series IGBT switch to replace the GTO switch is the most significant challenge. IGBTs have the advantages of lower gate drive and shorter turn off delay time.