Measurement of RF characteristics for Superconducting Quarter-wave Resonator

RF characteristics of unloaded quality factor (Q0) and accelerating electric field (Eacc) were measured for superconducting quarter-wave resonator (QWR) in order to verify the performance. For the accurate measurement of RF characteristics, the measurement method of Q0 based RF power and RF coupling coefficient was used, and the measurement uncertainty was calculated with statistics analysis of systematic error in RF measurement system. The superconducting QWR was designed with a resonant frequency of 101.28 MHz and an accelerating electric field (Eacc) of 6 MV/m at a cavity dissipation power of 10 W in the high-intensity and energy isotope separator online device (HIE-ISOLDE) project at CERN. Q-slopes and RF coupling coefficients were measured for three QWRs at the resonant frequency 101.28 MHz. Q0 values of QWRs were measured 4.55 × 108, 3.78 × 108 and 3.17 × 108 at the 6 MV/m, respectively, and the measurement uncertainty of Q0 and Eacc were calculated 2.92% and 3.32%. Performances of superconducting QWRs were acceptable to operate the beam acceleration with consideration of cryomodule capacity in HIEISOLDE project.