Nb/sub 3/Sn coating of high purity Nb cavities

The authors have developed a modified vapor diffusion technique using specially constructed UHV furnaces to produce uniform Nb/sub 3/Sn layers on 1- and 3-GHz accelerator cavities without losing the high thermal conductivity of the Nb wall. In a first experiment with a single-cell 3-GHz cavity of medium Nb purity (residual resistivity ratio, RRR=156) they have achieved E/sub acc/=10 MV/m with an 0.6- mu m-thick Nb/sub 3/Sn layer. This is so far the highest accelerating field for their Nb/sub 3/Sn cavities, but it is low compared to the 25 MV/m achieved in the same cavity before coating. Possible reasons for the reduced breakdown field for Nb/sub 3/Sn are discussed on the basis of the local thermal breakdown model.<
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