Start-to-end simulation of CAEP FEL-THz beamline

A THz free electron laser (FEL-THz) is being constructed in China Academy of Engineering Physics (CAEP) with the aim of proving high-power, monochromatic and tunable radiation for research in a variety of experimental fields. This facility consists of an injector equipped with a photo-cathode direct current gun, an achromatic transfer line, and an undulator for THz radiation. The physical design of the beamline is accomplished with the PARMELA and TRANSPORT programs. Start-to-end simulation is performed and the result is crosschecked with the codes of IMPACT-T and ELEGANT. The results show that it is feasible to achieve an electron beam with energy of 7~8 MeV, beam current of about 5 mA, and normalized transverse emittance typically below 10 mmmrad at the entrance of the undulator.