Magnetron sputtering configuration for coating 1.3 GHz cavities with a Nb film

In the framework of the ARES project and as possible application for the TESLA project, we are assembling, in the 2nd University of Rome, a system to study the deposition of Nb film on a TESLA type copper cavity. Magnetron sputtering to coat accelerating cavities with superconducting film was developed at CERN for 500 MHz cavities, three times larger than TESLA cavities; while it is relatively easy to scale the technique up to larger cavities (as for instance to the 350 MHz LEP cavities) there are some difficulties to scale it down, particularly concerning the coils located on the inside of the cathode used at CERN to stabilize the discharge, unless small permanent magnets are used that do not allow full control over all discharge parameters. A possible solution is to put the coils outside the cavity in a magnetic bottle configuration. A brief review on sputtering of cavities, the simulation of electron trajectories in a magnetic bottle and the sputtering test setup are described