Performance test of a 65-MW klystron unit relevant to the microwave source upgrade of the KEK 2.5-GeV linac

There is a plan to upgrade the Japan National Laboratory for High-Energy Physics (KEK) 2.5-GeV linear accelerator (linac) microwave source, which affects both the asymmetric B-factory two-ring collider project and the 3-GeV operation of the Photon Factory storage ring. The authors describe the upgrading of the microwave source as well as performance tests of a test station which was established in order to confirm the feasibility this upgrade. The required increase in the injection linac energy from the present 2.5 GeV to 4.25 GeV necessitates the replacement of the 30-MW klystrons with new 65-MW units. Since a total modification of the klystron modulator would be expensive, the output voltage and average power of the modulator have remained unchanged. An increase in the klystron beam voltage could only be obtained by increasing the pulse transformer step-up ratio from 1:12 to 1:15. A new test station using a 65-MW klystron was established to confirm stable operation of the modified unit. An output power of 58 MW with a 1- mu s duration was successfully generated in a preliminary test.<>