Eco-Friendly Bipolar Electrochemical Bulk Processing of SRF Cavities

The DOE seeks commercially viable, fabrication technologies for SRF cavities, specifically new or improved bulk processing technologies. Current methods, such as buffered chemical polishing (BCP), use high viscosity electrolytes containing hydrofluoric acid, which is not conducive to low-cost, high volume manufacturing and is potentially harmful to workers. The project team proposes to build upon recent work to develop a robust, high throughput vertical Bulk Electropolishing process for SRF cavities, based on the hydrofluoric acid-free Bipolar EP process, to replace BCP for single and nine-cell cavities at the alpha/beta scale. The development of Bipolar EP for both bulk (this program) and final (other programs) surface finishing steps, will enable a manufacturing process that utilizes the same chemistry for bulk and final polishing, with only a change in applied electric field parameters. This will enable a simple fluid management system, with minimal worker safety concerns and lower chemical and waste treatment costs. Phase I will first demonstrate the feasibility of the process on coupons to optimize Bipolar EP process parameters to achieve niobium removal rates that are compatible with bulk processing throughput rates, while maintaining desired surface finishes. Subsequently in Phase I, we will transition the Bipolar EP process from coupons to bulk processing of single-cell cavities, while maintaining the desired removal rates. The project team will determine the performance effect of the Bipolar EP Bulk Process via cavity testing, and develop a preliminary economic analysis showing the commercial viability of the technology as compared to conventional practice. Commercial Applications and Other Benefits: The proposed product is a cost effective and robust process for bulk processing of niobium SRF cavities. The market size for SRF cavities for the International Linear Collider is ~16,000 cavities, with applicability to many other cavity configurations and applications. Other markets for Bipolar EP include niobium-alloys that are hypoallergenic and commonly alloyed with titanium and zirconium to make implantable medical devices, and require HF acid for polishing. Elimination of HF acid for electropolishing of medical implants is an important need and represents a strong commercial opportunity with a US market of ~$45B by 2014.