HB650 tuner testing scheme with single-cell SCRF cavity

Tuners are used for resonance control of superconducting RF cavities, which are very sensitive towards frequency perturbation due to very high quality factor. RRCAT has embarked on development of tuners required for high beta (HB) 650 MHz SCRF cavities. This paper presents a unique way of tuner testing using 650 MHz single-cell RF cavity. Finite element analysis of tuner with single-cell HB650 cavity has been carried out for calculating its tuning characteristics. Motor-driver has been developed for the stepper motor which is used for slow or off-line tuning of the cavity. For fast tuning operation a piezo-controller has been developed to drive piezoes with half-sinusoidal waveform. HB650 tuner developed indigenously, assembled on a HB650 single cell RF cavity, has been tested initially at room temperature (300 K) for its tuning sensitivity and hysteresis. As an intermediate step, to check cryocompatibility of the mechanism, tuner with single cell cavity has been tested at LN2 temperature. Finally it will be tested at 2K in VTS in order to test the tuner under superconducting state of the cavity. (author)