Cost Reduction in Cavity Fabrication

Abstract In Europe and Japan there exist several companies which are qualified to fabricate superconducting cavities for accelerator application. Two different technologies are used: Niobium sputter coating of copper cavities or ebeam welding from solid Niobium. The first technology was used to fabricate the cavities for the LEP accelerating unit at CERN. These cavities are operated at an accelerating gradient up to 7 MV/m. At higher accelerating gradient cavities made from solid Niobium show a better performance. The required gradient of 23 MV/m at a quality factor of 1x10^10 could be demonstrated with many 9-cell cavities (1.3 GHZ) operated at the TESLA Test Facility (TTF). These cavities are fabricated from solid Niobium. Stringent vacuum requirements must be meet during welding the Niobium parts. Furthermore the Niobium parts must be handled with great care not to contaminate the later inner surface of the cavity. These conditions result in considerable effort during fabrication. Development of complex tools or installation of specialized e-beam welding facilities are too costly for the fabrication of only a small number (less than 100) of cavities. Therefore an industrial study was launched to investigate large scale fabrication methods of Niobium cavities. This study was carried out in order to create cost numbers for the production of 20000 resonators within three years for the TESLA linear collider project