{"record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"2a2ebfec9d9ef5e031ef9c369e9d9730dde2ff7d294c3615b5455ae45fb78ff9","created":"2026-10-03T07:17:56Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"f0dcd98ea3f480a29978270ee4f707893f499231d69956080d40c8cc0de38658","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"mechanism","assisted_by":[],"external_id":"beams.srf-cavities.nb3sn-early-quench","kind":"well-posed","literature_status":"open","n":"1","parents":[],"plain":"Nb3Sn should hold about twice the field of niobium, but real cavities fail at roughly half of niobium's best.","posed_since":"","precise":"Vapor-diffusion Nb3Sn films ($\\sim 2e-4\\,\\mathrm{cm}$ thick) on Nb cavities quench at $H_{\\mathrm{pk}} \\sim 800\\text{-}1200\\,\\mathrm{G}$, compared with a predicted $H_{\\mathrm{sh}}$ near $4000\\,\\mathrm{G}$. Identify the limiting mechanism (thin-grain regions, tin-depleted patches with low $H_c$, vortex entry at grain boundaries, thermal runaway in the low-conductivity film) and predict the quench field from measured film microstructure.","problem_ref":null,"references":"","settled_by":"Temperature mapping and post-test microscopy of quench sites in several cavities showing a single microstructural cause whose predicted threshold matches the quench field.","status_note":"Single-cell Nb3Sn cavities reached accelerating gradients of approximately $0.24\\,\\mathrm{MeV}/\\mathrm{cm}$ by the early 2020s; the gap to the predicted superheating field remained.","title":"Why Nb3Sn cavities quench far below their predicted field","topic_ref":"e80fdf5b356ba02d4b3990f8abe874d0448c454195c990a76c551f83781fb3d8"},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"4f417ef39b71df1359b3ada3072abd6de7bb4abfb2d85712e65ef4b26d9ce8f6","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"cc6155bf712627d1069e6ed622c40a1ecee784c7461128d513d240fc6e45da67","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"udxCdKiG0gFdoUd5_AvitvwblKc-BARJJSUcehGaAdqPcN6_wcQ_PpAXkJ3VBDqCnTYdpjCRz-CippcGIPfmAg"},"schema":"pubphys.envelope/1"},"record_hash":"4f417ef39b71df1359b3ada3072abd6de7bb4abfb2d85712e65ef4b26d9ce8f6","leaf_index":705}