Performance of the FEL cryomodules

The Thomas Jefferson National Accelerator Facility (Jefferson Lab, formerly known as CEBAF) is building a highly efficient, kilowatt-level infrared fr ee-electron laser, the IR Demo FEL. The IR FEL uses superconducting radio-f requency (SRF) cavities to accelerate the electron beam that provides energ y for the laser. These cavities provide the high-gradient acceleration for the high average currents necessary for a compact FEL design. Currently, a quarter cryomodule injector and a full eight-cavity cryomodule have been in stalled in the FEL linac. These units were tested as part of the IR FEL com missioning process. The main focus of these tests was to determine the maxi mum stable operating gradient. The average maximum gradient reached by thes e ten cavities was 11 MV/m. Other tests included measurement of cavity para meters such as the unloaded Q (Qo) vs, gradient, the input coupling, calibr ation of field probes and behavior of the tuner mechanisms. This paper pres ents the results of those tests.