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Title UHV arc for superconducting Niobium film deposition
Type Poster cavity design / fabrication / treatment
Abstract Copper RF cavities coated with thin niobium films are an interesting alternative to bulk-Nb ones, since Cu is much cheaper than Nb, has higher thermal conductivity and superior mechanical stability. Coating by the magnetron sputtering method was very successfully implemented at CERN to produce 350 Mhz, 7 MV/m accelerating cavities for LEP. Unfortunately, the degradation of the sputtered cavities quality factor with increasing cavity voltage limits their maximum useful gradient to approximately 15MV/m. The reason for the degradation being still not clear there are reasons to suspect that it may be connected to features of the sputtering process. An alternative powerful and versatile technique is vacuum arc coating. Its main advantages over standard sputtering are the ionized state of the evaporated material, the fact that no gas to sustain the discharge is required, a much higher energy of atoms reaching the substrate surface, the capability to achieve very high deposition rates and, when the arc is triggered with a laser, total cleanliness. We have shown that the technique produces bulk-like films suitable for superconducting applications. The main disadvantage is the production of macroparticles (or microdroplets) that could increase the film roughness and induce field emission. We present our recent results on the characterization of niobium film produced by UHV cathodic arc in different conditions and on the microdroplet problem.

List of authors...

Principle author first.

Last (Family) Name First Name (Initials only) Affiliation or Organization (abbreviations if possible)
Russo R INFN-Roma2
Catani L INFN-Roma2
Cianchi A INFN-Roma2
Polini R Uniroma2
Tazzari S INFN-Roma2
Tazzioli F LNF
Langner J IPJ
Sadowski M IPJ

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