{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"4548ebdc46377d13708673bac91b4970efe3da5a1a02b86e7298f950a7af1b8d","created":"2026-10-03T07:17:56Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"99c70fc1852ed9b0ab12549d3b765280376d381f5af718d0fc80b6cfa840f45b","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"mechanism","assisted_by":[],"external_id":"beams.nb3sn-cavities.q-slope","kind":"phenomenon","literature_status":"open","n":"1","parents":[],"plain":"Even before stopping, Nb3Sn cavities lose more energy as the field grows. The source of this extra loss is unclear.","posed_since":"","precise":"Nb3Sn cavities at 4.2 K and 1.3 GHz show $Q_{0}$ decreasing with $B_{\\mathrm{pk}}$ above $\\sim 300\\ \\text{to}\\ 500\\,\\mathrm{G}$. Determine whether this arises from grain-boundary Josephson weak links, vortex penetration at local defects, tin-poor phases, or nonlinear BCS response, with a model predicting $Q_{0}(B_{\\mathrm{pk}}, T)$.","problem_ref":null,"references":"","settled_by":"Measured $Q_{0}(B_{\\mathrm{pk}})$ for cavities with controlled grain size and stoichiometry matched by a predictive model.","status_note":"","title":"Origin of the field-dependent losses in Nb3Sn 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