Status of electron linac operation and THz source development at LEBRA in Nihon University

The 125 MeV electron linac at Laboratory for Electron Beam Research and Application (LEBRA) has operated for approximately 1100 h in 2017. The electron beam acceleration time was approximately 515 h which is about 30% longer than that in 2016 though the machine operation time in term of the klystron heater power supplies decreased. The no.1 klystron was renewed in December 2017 since the output RF window of the old one was damaged due to dielectric breakdowns, enabling the operation at an RF pulse width of 20 μs. In December 2017, a new terahertz-wave transport line was constructed in collaboration with AIST to use the coherent edge radiation generated at the exit of the 45° bending magnet located downstream of the free electron laser (FEL) undulator for users' experiments and the electron beam diagnostics. Demagnetization of the undulator permanent magnets was found by the field measurements using a Gauss meter, which is considered a cause of the FEL power deterioration in recent operations. (author)