{"record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"6d37705bce99b15029c23a032bab8b41a27f1696ac5979569da37c80f56f8a9a","created":"2026-10-15T23:43:22Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["4f417ef39b71df1359b3ada3072abd6de7bb4abfb2d85712e65ef4b26d9ce8f6","ce59fb6cd812fc05906d0c60a71c75ea22bc686bcf38e7c3ef7010834d98ee7b"],"salt":"86518255fb268bb9f434594ea16ecbb6b99a8510d07dd2dcc52db3bbc7d2db73","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":"2","parents":[],"plain":"$\\mathrm{Nb_3Sn}$ should hold about twice the field of niobium, but real cavities fail at roughly half of niobium's best.","posed_since":"","precise":"Vapor-diffusion $\\mathrm{Nb_3Sn}$ films ($\\sim 2 \\times 10^{-4}\\,\\mathrm{cm}$ 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":"4f417ef39b71df1359b3ada3072abd6de7bb4abfb2d85712e65ef4b26d9ce8f6","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 $\\mathrm{Nb_3Sn}$ 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 $\\mathrm{Nb_3Sn}$ cavities quench far below their predicted field","topic_ref":null},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"9b0ac20a67d78490be5c395eade5939a09ce72cceea0251ee0a48b31f96e28f0","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"8eb7f39eded657de60649d1ee7a7004dce7ef1c2c1cd1c4f9860378292c1219f","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"-zca2kfb0gWSMxGgAjr9TT2NeNj6T4jfDxwXPCI0PHTEdMRMpaFElRiD0310BsbO0ret-FrhAKdAH0CbFAPXBg"},"schema":"pubphys.envelope/1"},"record_hash":"9b0ac20a67d78490be5c395eade5939a09ce72cceea0251ee0a48b31f96e28f0","leaf_index":2538}