Welding of niobium cavities at CERN

During the last years different methods for the fabrication of single cell and multi-cell cavities of quasi-spherical shape from niobium or copper sheet material have been considered at CERN. Hydroforming of cells with a ratio of outer to inner diameter above 3 as needed for our cavity design appears difficult and too expensive. Therefore, the forming the half cells by spinning with a welding of cells along their equator has been applied. For niobium cavities Electron Beam Welding (EBW) and Tungsten Inert Gas (TIG) welding has been used for equatorial welds and for the welding of irises. In the following we describe a few technological details and present some results. (orig.)