{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"3412b074e97983fbe10569529452a58b2dd4ea4541bedc5e8254799b9160843d","created":"2026-10-03T07:17:56Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"a6eec9f49fa0c9aa4785d56953aedeaf756827e37f9d531ee02a3fe9bbe57a12","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"mechanism","assisted_by":[],"external_id":"beams.srf-cavities.high-field-q-slope","kind":"phenomenon","literature_status":"contested","n":"1","parents":[],"plain":"Above a certain field, niobium cavities start wasting far more energy; a two-day bake at 120 C removes the effect, and why it works is still debated.","posed_since":"","precise":"Electropolished bulk Nb cavities at $1.3\\,\\mathrm{GHz}$ and $T = 2\\,\\mathrm{K}$ show a steep drop of quality factor $Q_0$ above peak surface magnetic field $H_{\\mathrm{pk}} \\sim 900-1000\\,\\mathrm{G}$, removed by in-situ baking at $120\\,\\mathrm{C}$ for $\\sim 48\\,\\mathrm{h}$. Identify the mechanism (niobium nanohydride precipitation within ~1e-5 cm of the surface, oxygen or vacancy-hydrogen complexes, or other) with a model predicting the onset field and its dependence on bake temperature and duration.","problem_ref":null,"references":"","settled_by":"Depth-resolved measurement of hydrogen, oxygen and vacancy profiles before and after baking, correlated with $Q_0(H_{\\mathrm{pk}})$ of the same cavities and matched by a quantitative model.","status_note":"Hydride-precipitation and impurity (oxygen, vacancy-hydrogen) explanations each have supporting studies; no consensus was found in records checked through 2025.","title":"Mechanism of the high-field Q-slope and its cure by 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