Researches and preliminary experiments on copper-niobium sputtered low-β superconducting resonator

Superconducting resonator is the important component of a superconducting accelerator. The best choice of the acceleration cavity for heavy ion superconducting accelerator is quarter wave resonator (QWR). By sputtering a layer of niobium films of several microns on the OFHC copper substrate, good superconducting properties and acceleration properties of the cavity can be obtained. However, it is very difficult to get uniform niobium films by sputtering because the inner surface of the QWR is complicated. To deal with this problem, we developed a multiparameter adjusting method to control the sputtering process of different parts of the QWR. A layer of uniform niobium film with nice superconducting performance is obtained. The low temperature experiments with liquid helium show that the Cu-Nb QWR has good superconducting characters. The Q-value of the cavity is about 5 × 10⁸.