Improved surface treatment of the superconducting TESLA cavities
  The proposed linear electron-positron collider TESLA is based on 1.3 GHz superconducting niobium cavities for particle acceleration. For a centre-of-mass energy of 500 GeV, an accelerating field of 23.4 MV/m is required which is reliably achieved with a niobium surface preparation by chemical etching. An upgrade of the collider to 800 GeV requires an improved cavity preparation technique. In this paper, results are presented on single-cell cavities which demonstrate that fields of up to 40 MV/m are accessible by electrolytic polishing of the inner surface of the cavity. 
L. Lilje, C. Antoine, C. Benvenuti, D. Bloess, J. -P. Charrier, E.   Chiaveri, L. Ferreira, R. Losito, A. Matheisen, H. Prei...