Title: The influence of cooldown conditions at transition temperature on the quality factor of niobium sputtered quarter-wave resonators
Author: Pei Zhang
Abstract: Quarter-wave resonators (QWR) are to be used in the ongoing linac upgrade of the ISOLDE facility at CERN. The cavities are made of niobium sputtered on copper substrate. They will be operated at 101.28 MHz at 4.5 K providing 6 MV/m accelerating gradient with maximum 10 W power dissipation. In recent measurements, we found the thermal gradient along the cavity during the niobium superconducting transition has an impact on the cavity quality factor. The influence of external magnetic field on the cavity performance has also been observed for the sputtered cavities.