Electron beam dynamics through a return-arc and a deceleration path of the JAERI Energy-Recovery Linac

Hajima, Ryoichi; Minehara, Eisuke

An energy-recovery linac (ERL) for a high-power FEL has been developed at JAERI (Japan Atomic Energy Research Institute), and a research program towards 10 kW FEL is under progress. In the JAERI-ERL, an electron beam after the FEL interaction is transported through a triple-bend arc and re-injected to the main superconducting module, where the electrons are decelerated down to 2 MeV, same as the injection energy. Since the electron beam has large energy-spread introduced by FEL interaction, special attention should be paid to both transverse and longitudinal phase space manipulation through the return-arc and the deceleration path. We present the results of beam dynamics simulations coupled with a 1-D FEL code, and discuss the limitation of FEL extraction efficiency determined by phase space acceptance of the return path. The design of a beam dump at 2MeV is also described.