Status of High-Efficiency Klystron Development for the PLS-II and PAL-XFEL

We are developing a high-efficiency klystron for use in the PLS-II(Pohang Light Source II) and the PAL-XFEL in the Pohang Accelerator Laboratory. Since the PLS-II and the PAL-XFEL are already running with ~70 klystron modulator systems, newly developed klystrons should be designed to fit into existing installation spaces and power supplies, and their overall lengths(< 2 m) and beam perveances(2 upervs) should not be changed. In order to achieve the high efficiency with aforementioned boundary conditions, we are going to adopt a multi-cell output cavity in which, unlike those of the the SLAC X-band and KEK C-band klystrons, the cell frequencies are independently tuned to provide maximum beam-to-rf power conversion. In this article we report on our physics and engineering design efforts to achieve the high efficiency with minimum instabilities.