{"record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"00c236cf678277d0d8469b02d22dd0aaab7f8ced35407967c92ff8f3aac20117","created":"2026-10-03T07:17:56Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"6c4b141eb20caba65ce706a38b00f21dff22d93720d8726b380dbed2e02f0f1e","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"value","assisted_by":[],"external_id":"beams.rf-breakdown.magnetic-field-breakdown","kind":"well-posed","literature_status":"partially-resolved","n":"1","parents":[],"plain":"A muon collider needs accelerating cavities placed inside very strong magnets, and such cavities spark at lower fields than without the magnet.","posed_since":"","precise":"Vacuum normal-conducting cavities at $\\sim 200\\text{-}800\\,\\mathrm{MHz}$ in axial magnetic fields $B \\sim 3e4\\,\\mathrm{G}$ show reduced maximum gradient, attributed to field-emitted electrons focused by B onto the walls, causing local heating. Establish the scaling of the safe gradient with B, frequency and wall material up to $B \\sim 1e5\\,\\mathrm{G}$ and above, as required for 6D muon ionization cooling channels.","problem_ref":null,"references":"","settled_by":"Gradient-limit measurements versus B up to the cooling-channel field for at least two wall materials and frequencies, compared with an electron-focusing heating model.","status_note":"Beryllium-walled and high-pressure gas-filled cavities reached approximately $0.5\\,\\mathrm{MeV}/\\mathrm{cm}$ in fields near $3e4\\,\\mathrm{G}$ at the Fermilab MuCool Test Area (reported around 2020); higher fields remain untested.","title":"Breakdown limit of RF cavities inside strong solenoid fields","topic_ref":"29c52025bad0f3bb40505db955939f35befc6ea9256f5e4972142fac9de7c602"},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"92481a57e681bdbeb0e4ffcdd84b3a204ae4300ad00eca7869e464aa0b57a224","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"b78bf5027540c13e2f22f3bc95dc968e2a8686c3d7e068c87c9eb485768a7a4a","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"MTMvN7OJRu7Fo34t93tjtE7KY3BZjYzH7-VD8mIcqHy41AVGX-culg33wydUruDJHawNMI_8lUiqTVRer9V1BQ"},"schema":"pubphys.envelope/1"},"record_hash":"92481a57e681bdbeb0e4ffcdd84b3a204ae4300ad00eca7869e464aa0b57a224","leaf_index":695}