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Title UHV arc deposition for RF superconducting cavity
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 and the capability to achieve very high deposition rates. We describe here the apparata to arc deposit Nb films in UHV and in different ( planar, filtered and cylindrical) geometries. Because for igniting the arc a small plasma burst of a sufficient density to form a high-conductivity path between cathode and anode has to be produced, a Nd-YAG pulsed laser focused on the cathode surface is used that provides very reliable, totally clean triggering. The different systems are presented and discussed in particular in view of  the possibility of the RF cavity coating application.

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
Tazzari S INFN-Roma2
Tazzioli F LNF
Langner J IPJ
Sadowski M IPJ

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