Thermal Performance of the SNS Cryomodule

When complete, the Spallation Neutron Source (SNS) will provide a 1 GeV, 2 MW beam for experiments. One portion of the machine’s linac consists of over 80 Superconducting Radio‐Frequency (SRF) 805 MHz cavities housed in a total of 23 cryomodules (CMs) operating at 2.1 K. Minimization of the total heat load is critical to machine performance since the refrigerator capacity is fixed. The total heat load of the cryomodules consists of the fixed static load and the dynamic heat load, which is proportional to the cavity performance. The heat load of the cryomodules is the single largest load to the cooling circuits of the refrigerator. During acceptance testing at Jefferson Lab, a series of measurements have been taken on the prototype and first three production CMs. Calorimetric measurements of the primary heat load and shield heat load are presented and discussed. Temperature measurements taken allow a comparison between actual and predicted thermal performance of two components unique to this cryomodule design: the helium gas‐cooled fundamental power coupler (FPC) and the helium heat exchanger (HX).