{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"9d739fe1411336cdff698154a9bb71a352a3f1d24b07f5d143e1347b3402c7e1","created":"2026-10-03T07:17:56Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"25a6a09c3bac3ed6b206b908844095dc4adb88d0e9a03c6b21c23a1e5e5cb2e1","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"mechanism","assisted_by":[],"external_id":"beams.rf-breakdown.initiation-mechanism","kind":"phenomenon","literature_status":"open","n":"1","parents":[],"plain":"Breakdowns start at small spots on a polished copper surface, but which process lights the spark (electrons pulled out by the field, crystal defects moving to the surface, local melting) is not agreed.","posed_since":"","precise":"In Cu accelerating structures at 3-30 GHz, breakdown occurs at surface fields $eE_{s} \\sim 2-3\\,\\mathrm{MeV}/\\mathrm{cm}$, and Fowler-Nordheim fits of dark current give field-enhancement factors $\\beta \\sim 30-100$ although no protrusions of matching height are observed. Identify the sequence of processes (dislocation-driven surface roughening, field-emission heating of emitters, neutral evaporation, plasma ignition) that turns an intact surface into an arc, with a model that predicts the threshold field and its dependence on hardness and crystal structure of the metal.","problem_ref":null,"references":"","settled_by":"In-situ imaging of breakdown sites before and after the event together with a model that reproduces measured thresholds for at least two metals of different crystal structure.","status_note":"","title":"Microscopic mechanism that initiates vacuum RF breakdown on 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