Acid-Free Electropolishing of Nb Cavities

The DOE seeks commercially viable, fabrication technologies for SRF cavities, specifically eco-friendly final polishing technologies. Current methods, such as conventional and buffered electropolishing, 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 Final Electropolishing process for SRF cavities, based on an Acid-Free Bipolar Electropolishing process, to replace conventional electropolishing for single and nine- cell cavities at the alpha/beta scale. The development of Bipolar EP for final surface finishing step will enable a manufacturing process that controls costs and reduces the environmental and health hazards associated with using acid solutions. Phase I will first identify an electrolyte, then demonstrate the feasibility of the process on coupons to optimize Bipolar EP process parameters to achieve niobium final surface finishes desired by the SRF community. Subsequently in Phase I, we will transition the Bipolar EP process from coupons to electropolishing of single-cell cavities, while maintaining the desired surface finish. 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 final electropolishing 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 Acid-Free 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 acids for electropolishing of medical implants is an important need and represents a strong commercial opportunity with a US market of ~$45B by 2014.