Studies on the improvement of niobium-sputtered quarter wave resonator supercond ucting cavity

Quarter wave resonator (QWR) is the best choice of the acceleration cavity for heavy ion superconducting accelerator. Using dc bias-voltage sputtering system, w e can sputter niobium films of several microns on the oxygen-free high-conductiv ity copper(OFHC) substrate. Good superconducting properties and acceleration pro perties of the cavity can be obtained. But compared with niobium cavity, it has very low Q and Eacc. Niobium nitride (NbN) is a good superconducto r, and it has a higher superconducting transition temperature (Tc) th an pu re niobium. Through experiments, we find that the Tc transition point of n iobium films rises to about 9.6K by using NbN interlayer between OFHC substrate and niobium films. So using this method can improve the superconducting properti es and thus the acceleration properties.