{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"3b2dff38af6c67c30279a784287c579f5262c5fd57cbd0de621068e985189412","created":"2026-10-03T07:17:56Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"9381d566600634114fbe940b71a47ec7ab2c46ff1f1af1e33b94af3e5e4f832c","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"value","assisted_by":[],"external_id":"beams.sc-magnets.stress-degradation-limit","kind":"well-posed","literature_status":"open","n":"1","parents":[],"plain":"Nb3Sn is brittle, and the huge magnetic forces in a high-field magnet squeeze the cable until its ability to carry current is permanently damaged; where that threshold lies and what breaks first is uncertain.","posed_since":"","precise":"Rutherford cables of Nb3Sn filaments in epoxy-impregnated coils at fields up to $\\sim 1.6e5\\,\\mathrm{G}$ are under transverse stress of order $1.5e9 \\text{ to } 2e9\\,\\mathrm{dyn}/\\mathrm{cm}^{2}$ (approximate). Determine the stress at which the critical current degrades irreversibly, its dependence on filament layout, impregnation and temperature cycling, and the microscopic failure mode (filament cracking, void collapse, debonding), as a function that fixes the maximal practical dipole field.","problem_ref":null,"references":"","settled_by":"Critical-current measurements of cable stacks under calibrated transverse stress, combined with post-test microscopy of filament cracks and a model that reproduces the onset stress.","status_note":"","title":"Transverse-stress limit for irreversible degradation of Nb3Sn 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