Design and evaluation of a compact 50 MW rf source of the PF linac for the KEKB project

Abstract

A compact 50 MW rf source, an upgraded version of an existing rf source of the PF linac, has been developed for the KEKB project. The rf pulse-width requirement for the 50 MW klystron is 4 μs in order to be used with SLED-type rf compressors. On the basis of a computer simulation, the existing 30 MW klystron has succeeded to produce more than 51 MW at a 310 kV beam voltage with a 4 μs rf pulse width by optimizing the focusing magnetic field. Based on this result, we have designed and tested a new compact 50 MW klystron, the interaction region of which is the same as that of the 30 MW tube. In order to realize a practically reliable tube, we enlarged the cathode diameter, the gun housing and the insulation ceramic-seal. As a result, we have succeeded in obtaining a 50 MW output power with an rf pulse width of 4 μs and a more than 60 MW output power with an rf pulse width of 2 μs from this klystron. Compatibility between the 30 MW klystron and the 50 MW klystron has been aimed at for a socket assembly, such as a focusing electromagnet and a pulse-transformer assembly, with only a small change. These could lead to a compact rf source, which would save on upgrading costs. We can expect an easy construction method, which could be required to be conducted during an interval of machine operation for the Photon Factory.