Thermal performance of the CEBAF superconducting linac cryomodule

When complete, the Continuous Electron Beam Accelerator Facility (CEBAF) will be centered on a 4 GeV recirculating linac. Each of the two linacs contains 160 superconducting radio frequency (SRF) 1497 MHz niobium cavities in 20 cryomodules operating between 2 and 2.3 K. Minimization of the total heat load is critical to machine performance, since the refrigeration capacity is fixed. The total heat load of the cryomodule consists of the static load (fixed heat leak) and the dynamic load (proportional to the cavity performance Q0, or quality factor). The heat load of the cryomodules is the single largest load to both the primary and secondary cooling circuits of the refrigerator. The optimization of the thermal performance of the cryomodule considers recent test data of multilayer insulation (MLI) systems developed for the SSC, in addition to the effect of the dynamic heat load on the design of the cryostat. The design of the cryomodule and the measured thermal performance of the installed north and south linac cryomodules are discussed. The performance to date is shown to meet the design heat loads for the accelerator