{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"e32a001e566f413df80f112f0e37f8ebbb8355eeda47a3f1db55a9f8581f86e4","created":"2026-10-15T23:43:22Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["20271affdabc397cd87d7f5b81d8b355d39037ccf0dce7676738d06b6fc29573","ce59fb6cd812fc05906d0c60a71c75ea22bc686bcf38e7c3ef7010834d98ee7b"],"salt":"78400808eba9eb51f68319ac5912f0adc4a7dcdd511b95cdad47735b9d6c7ad2","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"yes-no","assisted_by":[],"external_id":"beams.srf-cavities.superheating-limit","kind":"well-posed","literature_status":"open","n":"2","parents":[],"plain":"A superconductor can carry an RF magnetic field only up to a maximum (the superheating field); thin layered coatings might push past niobium's value, but this has not been shown in a working cavity.","posed_since":"2006","precise":"The superheating field of clean Nb is $H_{\\mathrm{sh}}$ approximately 2000-2400 G at low T, and the best Nb cavities reach $H_{\\mathrm{pk}}$ near 2000 G. Determine whether superconductor-insulator-superconductor multilayers ($\\mathrm{Nb_3Sn}$, NbN or similar layers thinner than the London penetration depth on Nb) raise the attainable RF field above bulk Nb $H_{\\mathrm{sh}}$ in a cavity at $f \\sim 1\\, \\mathrm{GHz}$, and give the maximal field versus layer thickness and defect density.","problem_ref":"20271affdabc397cd87d7f5b81d8b355d39037ccf0dce7676738d06b6fc29573","references":"","settled_by":"A coated cavity sustaining $H_{pk}$ above the bulk Nb superheating field at $T \\sim 2\\,\\mathrm{K}$, with the field verified by calibrated RF measurement.","status_note":"","title":"Can multilayer coatings raise the RF field above niobium's 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