Test operation of ball-screw-type tuner for low-los high-gradient superconducting cavity at 77 K

Super-conducting Radio Frequency (SRF) 9-cell cavities have been developed in Low-Loss (LL) ICHIRO shape at KEK aiming at high-gradient operation for the International Linear Collider (ILC). One of the most important issues to realize high-gradient linac with SRF cavitiest in pulsed-mode operation is the compensation of the Lorentz detuning of cavities which amounts to 3 kHz at our goal of 45 MV/m acceleration field. None of tuners to date have achieved this specification. A coaxial ball- screw tuner was designed, fabricated and proven to reach this specification in room temperature. The performance was studied also at liquid-nitrogen temperature and the needed dynamic-range for 45 MV/m operation was proven at this temperature. The microphonic vibration was measured to be 100 Hz order in a test setup. In this paper, we describe these studies and evaluate the feasibility of ball-screw tuner operation at 2 K.