Recent developments in the high Q and high gradient frontier of SRF cavities have focused on altering the surface impurity profile through in-situ baking, furnace baking, and doping to introduce and diffuse impurities such as O, N and C. However, the precise role of each impurity in improving performance is not fully understood. We take a materials-focused approach to identifying the...
A program of quantitative measurements of magnetic flux expulsion on flat macroscopic samples has been used to assess and categorise magnetic expulsion efficiency. The measurement setup is a magnetic flux lens based on closed-topological heating/cooling through the material’s superconducting transition. This offers systematic and repeatable expulsion measurements for bulk, thin film and...
Two-level systems (TLS) have long been a catch-all explanation for RF loss and quantum decoherence in superconducting devices. In our study, the first to directly link TLS losses to a specific physical mechanism, we demonstrate that oxygen vacancies in the naturally formed Nb₂O₅ on oxidized niobium are a major driver of such dissipation. We performed sequential in situ vacuum-baking treatments...
We present trapped flux data of Nb3Sn samples prepared with sputtering and via bronze route. The data shows that during cooldown magnetic fields with magnitudes several times that of the earth’s magnetic field can be generated. As the sample becomes superconducting the fields are trapped and can be directly measured by our setup. In the data a correlation between field magnitude and the...
Measuring fundamental RF field limits of candidate superconductors for SRF cavities is challenging as local defects and thermal heating can lead to premature quench at field well below the ultimate limit of a superconducting material. Cornell has developed, fabricated, and commissioned a unique sample host cavity that allows for exposing superconducting material samples to very high RF fields...
Trapped vortices in superconductors introduce residual resistance in superconducting radio-frequency (SRF) cavities and disrupt the operation of superconducting quantum and digital electronic circuits. Understanding the detailed dynamics of trapped vortices under oscillating magnetic fields is essential for advancing these technologies. We have developed a near-field magnetic microwave...
SRF cavities are a critical technology both for particle accelerators, where they enable high energies and efficient operation, and superconducting quantum circuits, where they enable large coherence times for qubits. In both applications, the need for better performing cavities with higher quality factors is clear. The native oxide that forms on the surface of niobium may be the source of...
