Niobium Quarter-Wave Resonator Development for The Rare Isotope   Accelerator
  Two superconducting quarter-wave resonator (QWR) prototypes have been fabricated and tested. They operate at 80.5 MHz and 161 MHz and are optimised for beta = 0.085 and beta = 0.16, respectively. The prototypes are simplified versions without integrated helium vessels. In the first RF tests, the beta = 0.085 QWR reached a peak surface electric field (Ep) in excess of 30 MV/m, with an intrinsic quality factor (Q0) in excess of 1E9 at the design field of Ep = 20 MV/m. The beta = 0.16 QWR reached Ep = 20 MV/m with Q0 = 2.5E9. It is suspected that the performance of the latter cavity can be improved via better cooling of the Nb tuning plate and a better RF contact between the plate and the outer conductor. 
W. Hartung, J. Bierwagen, S. Bricker, J. Colthorp, C. Compton, T.   Grimm, S. Hitchcock, F. Marti, L. Saxton, R. C. York, A....