{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"7f07c119795d594ebf5925e8f570a0bedb325bae5233c0c061231d986d899a97","created":"2026-10-03T07:17:56Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"8e7e854e4609644f53d4a9761106c2d52534afc41ad7db94be68531567a92aa3","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":"1","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 (Nb3Sn, 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":null,"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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