Injector design for the 4GLS high average current loop

The proposed 4th Generation Light Source (4GLS) consists of three electron branches. We present the design of the injector for the High Average Current Loop which feeds spontaneous light sources and a Vacuum Ultraviolet FEL. The injector aims to provide 77 pC bunches at a repetition rate of up to 1.3 GHz which corresponds to an average current of 100 mA. It consists of a 500 kV GaAs based DC photocathode electron gun equipped with a photocathode preparation facility, followed by a normal- conducting buncher cavity and a 10 MeV superconducting RF booster. Simulations are presented which show the injector provides a beam with a normalised rms transverse emittance of less than 3 pi-mm-mrad and a bunch length of about 2 ps.