{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"23957d3e24de4ae217d5893fb17b2e80826e41c4cd722f3d96915d9044e3554d","created":"2026-10-15T23:43:22Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["456dcff03fdc27d3b30480cafee1b584f9a4a333cd77f2f78ab5a3fa27f2bb62","ce59fb6cd812fc05906d0c60a71c75ea22bc686bcf38e7c3ef7010834d98ee7b"],"salt":"c72bb225da6251680628500453e95d49411058a0db33bc190dfee735445e34a4","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":"2","parents":[],"plain":"Even before stopping, $\\mathrm{Nb_3Sn}$ cavities lose more energy as the field grows. The source of this extra loss is unclear.","posed_since":"","precise":"$\\mathrm{Nb_3Sn}$ 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":"456dcff03fdc27d3b30480cafee1b584f9a4a333cd77f2f78ab5a3fa27f2bb62","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 $\\mathrm{Nb_3Sn}$ 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