FIRST CRYOGENIC TESTS WITH JLAB'S NEW UPGRADE CAVITIES

Two types of 7-cell cavities have been developed for the upgrade of CEBAF to 12 GeV. The High Gradient type (HG) has been optimized with respect to the ratio of Epeak/Eacc. The Low Loss (LL) type has optimized shunt impedance and improved geometric factor. Each cavity type features four DESY-type coaxial Higher Order Mode (HOM) couplers and a waveguide input coupler. Design goals for these cavities have been set to Eacc = 20 MV/m with an intrinsic Qo of 8·10 9 at 2.05 K. A niobium prototype of each cavity has been fabricated at JLab and both cavities have been evaluated at cryogenic temperatures after appropriate surface treatment. In addition, pressure sensitivity as well as Lorentz force detuning were evaluated. The damping of approximately 20 HOMs has been measured to verify the room temperature data. Several single cell cavities were tested in addition to multi cell cavities. We present in this contribution a summary of tests performed on the prototypes of the proposed cavities.