Superconducting Quarter-Wave Resonators for the ATLAS Energy Upgrade

A set of six new 109 MHz β=0.15 superconducting (SC) quarter-wave resonators (QWR) has been built at ANL as part of an upgrade to the ATLAS superconducting heavy-ion linac at Argonne National Laboratory. The final cavity string assembly will use most of the techniques needed for the next generation of large high-performance ion linacs such as the U.S. Department of Energy's FRIB project. Single-cavity cold tests at T=4.5 K have been performed for 5 of 6 cavities. Tests were performed with a moveable coupler, rf pickup, and VCX fast tuner as required for the full 5-meter cryomodule assembly. The average maximum accelerating gradient of 6 cavities (5 new + 1 prototype), is EACC=10.6 MV/m (BPEAK=62 mT). Assembly of the clean cavity string has just begun using techniques which are fairly well developed based on many single cavity clean assemblies and one assembly of the entire string performed under non-clean conditions. Details on single cavity performance including high-field cw operation, microphonics and fast tuning are presented.