{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"af0879aa1d49541241b175b9b0953108f293a2aa1a3840afa79baaf959124b75","created":"2026-10-15T23:43:22Z","files":[],"origin":{"assisted_by":["ai:gpt-5.5"],"kind":"seed"},"parents":["cb5159aa4dd4a2477252029cc26eb709ba146ebcc08c01401fa20398fa2d68f4","ce59fb6cd812fc05906d0c60a71c75ea22bc686bcf38e7c3ef7010834d98ee7b"],"salt":"e3f274ce68bd5c97106ce624f2bd157fd9515d4db1541b55fb79984edde5e1ff","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"mechanism","assisted_by":["ai:gpt-5.5"],"external_id":"plasma.exb-low-temperature.anomalous-mobility-closure","kind":"phenomenon","literature_status":"open","n":"2","parents":[],"plain":"Thruster simulation codes currently need a hand-tuned correction factor for how easily electrons cross the magnetic field. A formula derived from physics would make the codes predictive.","posed_since":"","precise":"In Hall thrusters (radial $B$ of order 100 to 300 G, xenon propellant), the measured cross-field electron mobility exceeds the classical collisional value by one to three orders of magnitude and varies along the channel. Derive a closure $\\mu_{\\mathrm{perp}}(z)$ from local plasma parameters that, inserted in fluid or hybrid codes, predicts thrust, discharge current and breathing-mode oscillations to within 10 percent without tuning, across thrusters and operating points.","problem_ref":"cb5159aa4dd4a2477252029cc26eb709ba146ebcc08c01401fa20398fa2d68f4","references":"","settled_by":"A closure that predicts measured performance of at least two different thrusters across operating points without adjustment.","status_note":"3D particle-in-cell simulations in 2025-2026 resolve the electron drift instability and near-wall transport paths (e.g. arXiv:2603.14849), but no tuning-free closure exists.","title":"First-principles closure for cross-field electron mobility in Hall 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