PROGRESS IN THIN-FILM TECHNIQUES

Progress since the last Workshop is reported on superconducting (sc) a ccelerating RF cavities coated with thin films. The materials investig ated are Nb, Nb3Sn, NbN and NbTiN; the techniques applied are diffusio n from the vapour phase (Nb3Sn, NbN), the bronze process (Nb3Sn), and sputter deposition on a copper substrate (Nb, NbTiN). Specially design ed cavities for sample evaluation by RF methods have been developed (t riaxial cavity). New experimental techniques to assess the RF amplitud e dependence of the surface resistance are presented (with emphasis on niobium films sputter-deposited on copper). Evidence is increasing th at this amplitude dependence is caused by magnetic flux penetration in to the surface layer.