Muon spin rotation studies of niobium for superconducting RF applications

Abstract

In this work we investigate superconducting properties of niobium samples via application of the muon spin rotation/relaxation (muSR) technique. We employ for the first time the muSR technique to study samples that are cutout from large and small grain 1.5 GHz radio frequency (RF) single cell niobium cavities. The RF test of these cavities was accompanied by full temperature mapping to characterize the RF losses in each of the samples. Results of the muSR measurements show that standard cavity surface treatments like mild baking and buffered chemical polishing (BCP) performed on the studied samples affect their surface pinning strength. We find an interesting correlation between high field RF losses and field dependence of the sample magnetic volume fraction measured via muSR. The muSR line width observed in ZF-muSR measurements matches the behavior of Nb samples doped with minute amounts of Ta or N impurities. An upper bound for the upper critical field Hc2 of these cutouts is found.

20 pages, 14 figures

References in corpus (2)

• Muon spin rotation studies of electronic excitations and magnetism in the vortex cores of superconductors
• Proximity breakdown of hydrides in superconducting niobium cavities

Cited by in corpus (11)

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• Field of first flux entry and pinning strength of superconductors for RF application measured with muon spin rotation
• A New High Parallel-Field Spectrometer at TRIUMF's $\beta$-NMR Facility
• A low energy muon spin rotation and point contact tunneling study of niobium films prepared for superconducting cavities
• Evidence for Cooper Pair Diffraction on the Vortex Lattice of Superconducting Niobium
• Measurements of the first-flux-penetration field in surface-treated and coated Nb: Distinguishing between surface pinning and an interface energy barrier
• Coaxial multi-mode cavities for fundamental SRF research in an unprecedented parameter space
• Depth-resolved Characterization of Meissner Screening Breakdown in Surface Treated Niobium
• Influence of crystalline structure on RF dissipation in Niobium: flux trapping, hydride precipitate, doping behavior...