Niobium Coating of Cavities Using Cathodic Arc

Niobium thin film coated copper RF cavities are an interesting alternative to niobium bulk cavities for the development of high performance superconducting accelerators. The main limiting factor in their use is the degradation of the quality factor Q with increasing accelerating field (the ldquoQ-Sloperdquo). To try and overcome this limitation, we have developed an alternative coating technique based on a Cathodic Arc system working under UHV conditions (UHVCA). High quality Nb samples have been synthesized under different deposition angles and their characteristics are presented. The UHVCA technique has been used to deposit 1.3 GHz TESLA-type single cell cavities. To further improve cavity performance the first critical field has to be enhanced. The use of multilayers consisting of alternating insulating and superconducting layers may produce the desired enhancement providing that the superconducting layer thickness is smaller than the London penetration depth. To this aim, we present also the experimental characterization of the superconducting properties (T_C, B_C1) of Nb/AlOx/Nb multilayers.