{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"e06299ced96a684c6e438e75d80ab8c0fcee1dd52fac271f49b6e968b425796c","created":"2026-10-03T07:18:08Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011","c062acf8f46ff5531261ef4e58c7d1b7c756b77f6472a3e066b06c09f02d0ee1"],"salt":"f30c5fadaca12d8d7e0afb85a775afc14f38542924120534f25d1ce94f8f4f53","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"value","assisted_by":[],"external_id":"plasma.tokamak-confinement.lh-power-threshold","kind":"well-posed","literature_status":"open","n":"1","parents":[{"note":"","parent_revision":"c062acf8f46ff5531261ef4e58c7d1b7c756b77f6472a3e066b06c09f02d0ee1","relation":"special_case"}],"plain":"The heating power needed to enter H-mode is lowest at one particular plasma density and is about twice as large in hydrogen as in deuterium. Predicting it for ITER's hydrogen, helium and deuterium-tritium phases needs an explanation of both facts.","posed_since":"","precise":"The L-H threshold power $P_{\\mathrm{LH}}$ has a minimum at a device-dependent line-averaged density $n_{\\min}$ and is roughly a factor of 2 higher in hydrogen than in deuterium, an isotope dependence that the deuterium-based ITPA 2008 regression (Martin et al. 2008) does not contain. Derive $n_{\\min}$ and the isotope factor from first principles (for instance from the ion-electron heat exchange and edge ion heat flux) and predict $P_{\\mathrm{LH}}$ for ITER in H, He and D-T to within 25 percent.","problem_ref":null,"references":"","settled_by":"First-principles predictions of $n_{\\min}$ and the isotope factor confirmed on multiple devices and then by ITER non-active operation.","status_note":"","title":"Origin of the density minimum and isotope dependence of L-H 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