IMPROVEMENT OF THE LONG PULSE OPERATION OF THE FEL LINAC AT NIHON UNIVERSITY

Some improvements to the high power RF system of the 125 MeV linac have been performed to realize a stable long pulse operation of the linac. The breakdown of the klystron RF window occurred in 8 klystrons at early phase of the linac operation. However, the problem has been avoided by the improvement to the vacuum conductance around the RF windows and by a careful conditioning. The Mitsubishi PV3030 type klystrons, which were moved from KEK, have been operated successfully at the peak output RF power of 20 MW, the RF pulse width of 20 µs and the repetition rate of 12.5 Hz.