Design and fabrication of the 2×4-cell superconducting linac module for the free-electron laser

A 2×4-cell superconducting linac module for the THz-FEL facility has been developed at the China Academy of Engineering Physics, which is expected to provide 6-8 MeV quasi-CW electron beams with an average current of 1-5 mA. The module consists of two 4-cell SRF cavities, two main couplers, two tuners and a cryostat. The design, fabrication and performance test of these components is presented in this paper. The test results reveal that all these components have reached their design goals and the module has also been assembled and horizontal tested at Chengdu. The gradients of both cavities at 2 K reach 10 MV/m, which meets our requirements. Currently beam-loading commissioning is underway.