(Industrial Electrochemistry and Electrochemical Engineering Division New Electrochemical Technology (NET) Award) Pulse Reverse HF-Free Electropolishing of Niobium Superconducting Radio Frequency (SRF) Cavities for Nuclear Physics and High Energy Physics Applications

Abstract

On behalf of Faraday Technology, Inc., we are honored to receive the 2021 New Electrochemical Technology (NET) award of the Industrial Electrochemistry & Electrochemical Engineering (IE&EE) division for pulse reverse FARADAYIC® HF-FREE Electropolishing of niobium SRF cavities. The NET award was endowed by the Dow Chemical Company Foundation to recognize significant advances in industrial electrochemistry. We addressed the subject innovation as a multidisciplinary team of electrochemists, engineers and technologists.Niobium superconducting radio frequency (SRF) cavities are used in particle accelerators such as the Large Hadron Collider (LHC) to support nuclear/high energy physics applications. To achieve their required performance, the niobium SRF cavities are electropolished using nine-parts sulfuric acid to one-part hydrofluoric acid.[1] The conventional process follows the well-established “viscous salt-film” model for electropolishing.[2] The conventional electrolyte imparts an extreme hazard to workers requiring costly safety protocols with extensive worker protection (see Fig. 1a).[3] ,[4] To commercialize niobium SRF cavity electropolishing, a simpler, cost-effective industrially compatible process was required.We developed a pulse reverse process to electropolish niobium coupons in low concentration (<5 wt%) aqueous sulfuric acid electrolytes devoid of hydrofluoric acid.[5] The surface roughness was the same as that observed using conventional DC electropolishing.[6] We transitioned the work from coupons to single-cell niobium cavities SRF and the performance was the highest observed at the DOE’s Fermi National Accelerator Facility.[7] ,[8] Due to the avoidance of the safety protocols associated with the conventional process (see Fig. 1b), the capital and operating costs of the pulse reverse electropolishing process were considerably less than the conventional process.[9] Finally, the pulse reverse process was patented and transitioned to DOE’s Thomas Jefferson National Accelerator Facility.[10] ,[11] Finally, the pulse reverse process was adapted to other strongly passive materials.While reviewing the technology developments leading to and associated with the niobium pulse reverse electropolishing process, we will illustrate lessons learned during the development of industrial innovations.[12] [1] H. Tian, S. Corcoran, C. Reece, and M. Kelly, J. Electrochem. Soc., 155, D563 (2008). [2] P. A. Jacquet, Trans. Electrochem. Soc., 69, 629 (1936). [3] T. Dote and K. Kono, Jap. J. Occupational Medicine and Traumatology, 52, 3, 189 (2004). [4] J. Mammoser, “Chemical Safety Awareness for SRF Cavity Work” U.S. Particle Accelerator School, January 19, 2015 (accessed June 9, 2020) https://www.jlab.org/indico/event/98/ other-view?fr=no&detailLevel=contribution&view=standard& showSession=all&showDate=all [5] M. Inman, E. J. Taylor, and T. D. Hall, J. Electrochem. Soc., 160, E94 (2013). [6] M. Inman, T. Hall, E. J. Taylor, C. Reece, and O. Trofimova, Paper TOPO012, Proc. SRF2011, Chicago, IL (2011). [7] E. J. Taylor, T. Hall, M. Inman, S. Snyder, and A. Rowe, Electropolishing of Niobium SRF Cavities in Low Viscosity Aqueous Electrolytes without Hydroflouric Acid, Paper TUP054, Proc. SRF2013, Paris, France, Sept 2013. (ISBN 978- 3-95450-143-4) [8] A. Rowe, A. Grassellino, T. Hall, M. Inman, S. Snyder, and E. Taylor, Paper No. TUIOC02, Proc. SRF2013, Paris, France, Sept 2013. (ISBN 978-3-95450-143-4) [9] E. J. Taylor, M. Inman, T. Hall, S. Snyder, A. Rowe, and D. Holmes, Paper MOPB092, Proc. SRF2015, Whistler, BC, Canada (2015). [10] E. J. Taylor, M. E. Inman, and T. D. Hall, U.S. Pat. No. 9,006,147 issued April 14, 2015. [11] E. J. Taylor, M. E. Inman, and T. D. Hall, U.S. Pat. No. 9,987,699 issued June 5, 2018. [12] E.J. Taylor, M.E. Inman, H.M. Garich, H.A. McCrabb, S.T. Snyder, T.D. Hall in Electrochemical Engineering: The Path from Discovery to Product Alkire, Bartlett, Koper (eds) Wiley-VCH (2019). Figure 1