Superconducting Resonators for the University of Washington Booster Linac

We have developed two models of a 150 MHz quarter wave resonator -- one with optimum beta=0.10 and one with optimum beta=0.21. These are lead-plated copper structures. The prototype beta=0.10 resonator was tested successfully a year ago and gave average accelerating fields of 3.5 MV/m with 4.2 Watts dissipated. It is quite similar to the resonator developed by the second and third authors.1 We have made and tested several more of this model. A prototype beta=0.21 resonator has been completed, but weld flaws have prevented definitive tests. In order to minimize surface electric fields in the high-beta resonator, there were some modifications in the drift tube shape beyond those required to change the optimum beta. These quarter wave resonators have a wide transit time factor curve and are extremely rigid mechanically. Variations in eigen-frequency due to mechanical vibrations are less than 1 Hertz. Maximum attainable fields are limited by field emission.