{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"bc6bd3fe35489481f6a8030b380b2a13dfb319bb8e7f23945cc36398a2df04c2","created":"2026-10-03T07:18:08Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"7380569c14895ee27bfa4b1135d795fa90f3640d01ff55e50570c9a3729d4593","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"mechanism","assisted_by":[],"external_id":"plasma.exb-low-temperature.anomalous-mobility-closure","kind":"phenomenon","literature_status":"open","n":"1","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_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":null,"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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