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Accepted · first revision · record

Title: Origin of the density minimum and isotope dependence of L-H threshold
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.
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.
Settled by: First-principles predictions of $n_{\min}$ and the isotope factor confirmed on multiple devices and then by ITER non-active operation.
Kind: well-posed
Answer type: value
References: (empty)
Literature status: open
Status note: (empty)
Posed since: (empty)