Development of Seamless Niobium Cavities for Accelerator Applications

Superconducting niobium cavities for application in particle accelerators are usually fabricated by standard techniques such as forming of subcomponents by deep drawing and joining by electron beam welding. Even though these techniques are being used successfully in many larger-scale accelerator projects and improvements in accelerating gradients have been achieved over the last several years, there are often still problems with making defect-free electron beam welds. In addition, the manufacturing costs for such devices are significant and a drastic reduction in production costs is a necessary condition for future very large scale applications in, e.g., linear colliders. Seamless cavities made by spinning from a single sheet of material will dramatically reduce the fabrication costs and eliminate any problems associated with electron beam welding. The fabrication technique for seamless niobium cavities has been developed over the last few years at INFN LNL and several proto type single-cells of different material thickness and purity have been manufactured as well as a 5-cell cavity. Results from tests on these cavities after application of surface treatment techniques, such as buffered chemical polishing, ''barrel polishing'' and high temperature heat treatments, are discussed in this contribution. Q-values as high as 1011 and accelerating gradients up to Eacc approximately 30 MV/m have been measured