Seamless SRF Cavity Fabrication by Spin-Necking and Hydroforming

Superconducting radio frequency (SRF) cavities for use in the International Linear Collider (ILC) are currently fabricated by electron-beam welding of press-formed half-cell cups. Cavities produced in this method experience weld-related defects that limit accelerator performance and increase the cost of supplying the SRF system to the end user. E-beam welding in its optimum state is expensive and causes additional manufacturing risk and lead time. Development of an alternate method that increases first and second pass production yields offers the benefit of cost reduction to the end-user which will have significant public benefit. This project will develop a weld-free cavity forming process which will eliminate welds and weld-related defects and therefore reduce cavity cost. The primary reference model will be the 1.3 GHz 9-cell TESLA-style SRF cavity but the objective will be to produce a 3-cell cavity. The sequential forming processes of spin-necking and hydroforming will be employed to produce cavities from a single, weld-free tube of cavity metal. Cavity irises will be mechanically formed on a spinning machine and cavity equators will be formed through a hydroforming process. In Phase I, successful development of a spin-necking process to produce the iris geometry at the actual ILC scale was completed. 3-cell cavity pre-forms which are ready for the subsequent hydroforming process were produced. Detailed design of a production hydroforming machine for high-rate production of ILC cavities was completed. Numerical modeling was performed to optimize both spin-necking and hydroforming for further development in Phase II. In Phase II, the spin-necking operation will be further optimized and completed to form iris sections for 3-cell cavity. A hydroforming system will be built for the fabrication of 3-cell ILC cavities. Phase II development will be conducted with steel, copper and niobium seamless tubes. Nb 3-cell cavity will be tested for its SRF performance at a U.S. National Lab.