The First Beam Recirculation and Beam Tuning in the Compact ERL at KEK

Superconducting(SC)-linac-based light sources, which can produce ultra-brilliant photon beams in CW operation, are attracting worldwide attention. In KEK, we have been conducting R&D; efforts towards the energy-recovery-linac(ERL)-based light source* since 2006. To demonstrate the key technologies for the ERL, we constructed the Compact ERL (cERL)** from 2009 to 2013. In the cERL, high-brightness CW electron beams are produced using a 500-kV photocathode DC gun. The beams are accelerated using SC cavities, transported through a recirculation loop, decelerated in the SC cavities, and dumped. In the February of 2014, we succeeded in accelerating and recirculating the CW beams of 4.5 micro-amperes in the cERL; the beams were successfully transported from the gun to the beam dump under energy recovery operation in the main linac. Then, precise tuning of beam optics and diagnostics of beam properties are under way. We report our experience on the beam commissioning, as well as the results of initial measurements of beam properties