{"record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"27e53b21ecf0781f9f2aa55c88771381ecedecb72cfc54de8102ac72fd5d84de","created":"2026-10-15T23:43:22Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["92481a57e681bdbeb0e4ffcdd84b3a204ae4300ad00eca7869e464aa0b57a224","ce59fb6cd812fc05906d0c60a71c75ea22bc686bcf38e7c3ef7010834d98ee7b"],"salt":"008c1ec116944a9c13bb725b441de34b999896bca3411dcccbdd0b364ec4cabb","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":"2","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 $B \\sim 3 \\times 10^{4}\\,\\mathrm{G}$ 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 $B \\sim 10^{5}\\,\\mathrm{G}$ and above, as required for 6D muon ionization cooling channels.","problem_ref":"92481a57e681bdbeb0e4ffcdd84b3a204ae4300ad00eca7869e464aa0b57a224","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 $3 \\times 10^{4}\\,\\mathrm{G}$ 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":null},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"33483c883593db903c75ad06709c85ec9efbce09ea57330fc4f272c937fb32ea","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"6d28c5d39bd43e85f9b7d0af4ec272a22d032814dfca3e84b2611a91e085f4c8","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"B_9edJl2F5sw6q_RFNIiIci3dZAYJ5rCaU7k6VshhOidC4HsAKy13d7mfdc-SN3Fqi2JG1M1jlM0zAo94lAnAQ"},"schema":"pubphys.envelope/1"},"record_hash":"33483c883593db903c75ad06709c85ec9efbce09ea57330fc4f272c937fb32ea","leaf_index":2520}