Study of NbTiN coatings by reactive magnetron sputtering for the production of 1.5 GHz superconducting accelerating cavities

The production of thin films of Nb.35Ti.65N by magnetron sputtering is being studied for application to the realisation of 1.5 GHz accelerating cavities. Samples produced in a sputtering chamber havin g the same geometry as the RF resonator reached a Tc value of 15.5 K, a RRR of 1.45 and a low temperature DC resistivity of 35 mWcm. With the parameters optimised in this way, a coating was produced i nside a seamless copper cavity: the RF test showed a Tc for the cavity of 14.2 K, a residual resistance at low field of about 350 nW and a BCS resistance at 4.2 K of 55 nW. The latter figure, compared to the RBCS of Nb/Cu and bulk Nb resonators of the same frequency (about 400 nW and 900 nW respectively), confirms the potentiality of NbTiN for applications at 4.2 K. However, improvements on the res idual resistance and the dependence of the resistance as a function of the accelerating field are still necessary to get an overall performance comparable to that of standard Nb resonators.