{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"a8a4095439e62f6ea0ce2ae07e0192f76a5c07d0583853b2a853eb4c03fee08a","created":"2026-10-03T07:17:56Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"a9c0facd74dba02204fed823ee6f73c6cde5881456c9223cf8e23bb6692f840b","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"mechanism","assisted_by":[],"external_id":"beams.superheating-field.nb-gap","kind":"phenomenon","literature_status":"open","n":"1","parents":[],"plain":"Theory gives niobium a maximum surface field of about 2400 G at low temperature, but the best cavities stop near 2000 G. The missing margin is not understood.","posed_since":"","precise":"For clean Nb ($\\kappa \\sim 1$) Ginzburg-Landau and Eilenberger theory give $H_{\\mathrm{sh}}(0) \\sim 2300\\text{ to }2400\\,\\mathrm{G}$, while record cavities quench near $B_{\\mathrm{pk}} \\sim 1900\\text{ to }2100\\,\\mathrm{G}$. Determine whether the gap is caused by local defects that lower the vortex-entry barrier, by thermal runaway at hot spots, or by an intrinsic reduction of $H_{\\mathrm{sh}}$ at GHz frequencies, and give the expected achievable field for an ideal surface.","problem_ref":null,"references":"","settled_by":"Quench-site imaging and pulsed high-power measurements that separate thermal from magnetic quench, compared with theory for the measured surface.","status_note":"","title":"Why niobium cavities quench below the predicted superheating 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