Biased deposition of Nb-on-Cu for SRF accelerators

The DOE High Energy Physics HEP) program seeks to develop advanced accelerator technologies that reduce overall machine size and cost, and also to develop new concepts and capabilities that further scientific and commercial goals beyond HEPs discovery science mission. Superconducting Radiofrequency Accelerators consume much less power than room temperature accelerators, so can one day replace larger accelerators used in medicine and industry. Breakthroughs are needed, such as replacement of costly bulk niobium cavities by cheaper copper cavities that have a skin of niobium or higher temperature superconductors that reduce cryogenic costs. In the course of prior SBIR funded activity, and with the benefit of several other unrelated SBIR contracts from the US Navy and USAF), AASC has built up a versatile suite of high vacuum coating chambers. This suite, described further in the Facilities section, represents a capital cost of ~$1M. AASC sees an opportunity to support the SRF community by developing next- generation SRF superconductors. AASC has built relationships within the SRF community including Fermilab, LANL, JLab, HZB and CERN, while participating in DOE SBIR efforts related to SRF technologies. The innovative enhancement to the energetic condensation process proposed here will be provided by applying a bias to the cavity during the deposition step. The bias offers two potential advantages: 1) The bias increases the incident energy of the Nb ions, leading to a narrower energy spread and reduced compressive stress in the film. 2) The bias creates a thin plasma sheath at the cavity inner surface that draws ions to the surface at normal incidence. Various governments alone are expected to invest $1B over the next decade or so into superconducting accelerators. Private sector investment would match or exceed that with breakthroughs. AASC would license its knowhow and patents to larger companies so as to have an impact on this opportunity.