PROGRESS OF NB/CU TECHNOLOGY WITH 1.5 GHZ CAVITIES

The residual resistance of Nb/Cu cavities increases exponentially at high RF field. Two main possible causes have been investigated in detail: the hydrogen incorporated in the film during the sputtering process and the surface roughness induced by the substrate. The latter has been reduced with an optimised electropolishing technique, which couples laboratory analyses of the electrical characteristics of the bath with numerical simulations of the actual process. The hydrogen content of the film can be reduced by increasing the pumping speed during deposition, either in the form of a suitable getter underlayer or of an appendage getter pump. The main results from these studies will be presented, together with other minor developments.