Speaker:

• Daniel Bafia, Associate Scientist

• Superconducting Quantum Materials and Systems Division

• Fermilab

Abstract:

This presentation will highlight recent R&D efforts at Fermilab focused on niobium superconducting radio-frequency cavities for high Q and high gradient accelerator applications, with extensions to quantum information science. New insights into RF dissipation are obtained through surface processing approaches including nitrogen incorporation, controlled oxygen diffusion, and optimized electropolishing, which enable systematic reduction of surface resistance while preserving strong high-field performance. These results are enabled by combining precision cryogenic RF measurements with advanced materials characterization. The same processing approaches demonstrate adaptability across cavity frequencies and geometries, including recent studies on non-elliptical structures such as the barrel cell cavity developed at CERN, underscoring their relevance to evolving accelerator concepts and ongoing collaborative efforts. In alignment with these efforts, Fermilab is contributing to the FCC 800 MHz SRF program, where high-Q processing strategies are being explored in collaboration with CERN across both single-cell and multicell cavity development. This work builds on high-Q recipes first developed at Fermilab and supports their extension toward large-scale accelerator applications. In parallel, variants of these resonant structures not only enable ultra-low-loss, long-coherence quantum systems, but also serve as highly sensitive testbeds for materials characterization. By reducing complex multilayer devices to controlled single-interface geometries, key loss channels associated with amorphous niobium oxide, niobium hydrides, and dielectric substrates can be directly identified and quantified. Together, these results establish a materials-driven framework for controlling dissipation in superconducting resonators. Beyond accelerators, this level of control enhances sensitivity in dark sector searches, highlighting the broader impact of SRF technology across multiple frontiers of physics.

ATS Seminar Organisers
A. Dallocchio (EN), E. Metral (BE),  T. Stora (SY), A. Sublet (TE)