SPUTTER-COATED SUPERCONDUCTING RF CAVITIES FOR LEP - A TECHNOLOGICAL CHALLENGE

For increasing the energy of the Large Electron Positron Ring (LEP) at CERN superconducting accelerating cavities are being installed. Most of the 216 cavities, developed at CERN and manufactured in industry, h ave undergone successful acceptance tests. By sputter-coating high-pur ity niobium onto a copper substrate accelerating fields of 6 MV m(-1) with a quality factor Q(0) of 3.4 10(9) at 4.5 K and at a frequency of 350 Mhz were obtained. To reach these specifications it was necessary to develop surface preparation and sputtering techniques able to cove r the 5.5 m(2) of a cavity with a defect-free niobium layer of 1.5 mm thickness. Assembly and all preparations have to be done in a clean ro om of class 100. The cavities work in the ultra-high vacuum (similar t o 10(-10) mb) of the LEP ring. The working temperature is 4.5 K. Highe r performance for a low price has been obtained as compared to that fo r cavities made of niobium sheet material. Copyright (C) 1996 Elsevier Science Ltd.