{"record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"b32b9cd558dfec191af4aaf879a4743acc0be871c8c4021e4a76824de18c027c","created":"2026-10-15T23:43:22Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["96660c049558ecbf4ad4f4d3d86804236ec388109cc690b65a10048f2ab9e25b","ce59fb6cd812fc05906d0c60a71c75ea22bc686bcf38e7c3ef7010834d98ee7b"],"salt":"d17ea1fce0707333446b3d8f76818cbdfad6e4d57c32b318bfbd2382fe144d6a","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"mechanism","assisted_by":[],"external_id":"beams.srf-cavities.thin-film-q-slope","kind":"phenomenon","literature_status":"contested","n":"2","parents":[],"plain":"Cavities made by coating copper with a thin niobium film are cheaper and better cooled than solid niobium, but their energy loss rises steeply with field, for reasons still argued.","posed_since":"","precise":"Sputtered Nb films $\\sim 10^{-4} \\text{ to } 5 \\times 10^{-4}\\,\\mathrm{cm}$ thick on Cu cavities, as used at LEP, LHC and HIE-ISOLDE, show surface resistance $R_{\\mathrm{s}}$ rising roughly linearly with RF field from $H_{\\mathrm{pk}}$ of a few hundred G, unlike bulk Nb. Identify the mechanism (grain-boundary weak links and local hot spots, trapped flux in a granular film, poor film-substrate thermal contact, or other) and predict $R_{\\mathrm{s}}(H)$ from measured film microstructure for different deposition methods, including high-power impulse magnetron sputtering.","problem_ref":"96660c049558ecbf4ad4f4d3d86804236ec388109cc690b65a10048f2ab9e25b","references":"","settled_by":"$R_s(H)$ of cavities with controlled grain size and grain-boundary density, matched by a model fixed before the tests.","status_note":"A 2022 model (Ramiere, Antoine, Amrit, Phys. Rev. Accel. Beams 25, 022001, https://doi.org/10.1103/PhysRevAccelBeams.25.022001) attributed the slope to hot spots in granular films; competing explanations persist.","title":"Origin of the medium-field Q-slope in niobium-on-copper film cavities","topic_ref":null},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"cda6b59ea5bbf3dcb8e6dea45713b43fa52fa2e647b2e71fbd572058495011b3","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"969df257b4bf14c6547dd506591f05526f867caf19f680e2596b88885595895d","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"mxr4luH3iirk1_vHFw4qyOus7IYZGQDhfvqxS5kuPmBnGcU9v3xVvVu-D0Ijm8gJ7oKUkaFg7xeGzj8ezjMdCQ"},"schema":"pubphys.envelope/1"},"record_hash":"cda6b59ea5bbf3dcb8e6dea45713b43fa52fa2e647b2e71fbd572058495011b3","leaf_index":2544}