Status report of 125 MeV electron linac at Nihon University

The 125 MeV electron linac at Laboratory for Electron Beam Research and Application (LEBRA) has operated for approximately 1263 h in 2018. The electron beam acceleration time was approximately 358 h, which is about 30% shorter than that in 2017. Frequent dielectric breakdowns occurred at the RF output window of the klystron no.1 in September 2018. After the conditioning carried out for 2 months, the normal operation at the RF output power of 18 MW with the RF pulse duration of 20 μs was resumed. Immediately after the recovery of klystron no.1, leakage of the cooling water of the klystron no.2 focusing solenoid was found out at around the welding area of the cooling water pipe that was covered under the lead radiation shield. The solenoid required to be replaced with a new one. The klystron no.2 was also replaced because of the damage in the RF output window. It took about 4 months before the conditioning of the klystron no.2 started since the leakage of the cooling water. The klystron no.1 had not operated until the recovery of the klystron no.2. Presently, both klystrons are under the conditioning in parallel. The electron beam acceleration time was greatly reduced because of the conditioning of the klystrons for a long time. (author)