1 mA STABLE ENERGY RECOVERY BEAM OPERATIONWITH SMALL BEAM EMITTANCE

A compact energy-recovery linac (cERL) has been operating since 2013 at KEK to develop critical components for ERL facilities. To achieve a high averaged beam current of 1 mA with continuous-wave (CW) beam pattern while keeping small emittance from 500 kV DC-photocathode gun, it is essential to design and perform a beam-tuning at low-energy beam transport. Also, we found that the combination of beam collimators and the various kind of beam-tuning can improve the beam-loss ratio below 10−7 order. Sometimes the cERL has been operated under wide variety of machine parameters, for example, the highest total beam energy is decreased from 20 MeV to 17.6 MeV depending on a condition of super-conducting cavities, and the beam rep-rate of 1300 MHz or 162.5 MHz depending on the purpose of CW experiments. In each operational parameters, we successfully conducted the 1 mA CW operation and the efficiency of the energy recovery was confirmed better than 99.9 %.