Coaxial Energetic Deposition as a Means to Produce Superconducting Niobium Thin Films for Large Particle Accelerators

Summary form only given. Superconducting radio-frequency (SRF) particle accelerators rely on bulk Niobium cavities to accelerate the particle beam. Given that the London penetration depth for the superconductor is less than 100 nm, most of the costly bulk material is wasted. One alternative is to coat cheaper Copper structures with a thin film of Niobium. The Niobium coated Copper cavities benefit from the superior thermal properties of Copper and reduced cost of Copper (~$3/lb) over Niobium (~$300/lb). For a Niobium coated Copper cavity to replace bulk Niobium, coated cavities must match the performance of existing bulk cavities. Key performance specifications include critical temperature, thermal dissipation and quality factor. Alameda Applied Sciences Corporation, in collaboration with Thomas Jefferson National Accelerator Facility, has used a coaxial cathodic arc method to deposit the superconducting Niobium thin film on witness plates. In this study, the rotational speed and axial speed of the arc are measured to assess their role in the creation of Nb fims by measuring the ambient temperature thin films properties and when possible, the superconducting properties. The data suggest superior Niobium thin films are produced when the rotational speed of the arc is maximized. This collaboration has demonstrated thin film Niobium that matches the critical temperature of bulk Niobium cavities and exhibits a residual resistance ratio (RRR), a measure of the thermal dissipation, of nearly 40. The goal for the program is to approach a RRR of 200.