{"record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"4f6f9b931bf36cebcb7c30e1610c97170311ab04f283c2962ebbc64deaf78401","created":"2026-10-03T07:17:56Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"9c30aa98046d65534db891e5fa8245e671ea84121924c59b0bb75db149a9cff7","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":"1","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 $\\sim 1e-4 \\text{ to } 5e-4\\,\\mathrm{cm}$ 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":null,"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":"e80fdf5b356ba02d4b3990f8abe874d0448c454195c990a76c551f83781fb3d8"},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"96660c049558ecbf4ad4f4d3d86804236ec388109cc690b65a10048f2ab9e25b","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"846039327617470c403de213608da1a39f78cda449326c466a6acf3963bfd864","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"1qyNWwKiQZIDk3-vGD6T_MzOPuFzjuwC7gJsntezv26szFXIgvxozqijMiQErB2nXJrvQDsEwYjnhEANwrEvDA"},"schema":"pubphys.envelope/1"},"record_hash":"96660c049558ecbf4ad4f4d3d86804236ec388109cc690b65a10048f2ab9e25b","leaf_index":708}