Power requirement for accessing the H-mode in ITER

TLDR

The study examines how density and magnetic field effects influence the accessibility of the H‑mode regime in ITER plasmas. Statistical analysis of the international H‑mode threshold power database is used to determine the input power requirements for accessing and sustaining H‑mode at low density in ITER. A revised scaling law predicts ITER H‑mode threshold powers of ~52 MW at ne = 0.5×10²⁰ m⁻³ and ~86 MW at ne = 1.0×10²⁰ m⁻³, with the threshold’s density dependence growing with plasma size and magnetic field, and observations that present devices typically operate at >1.5× threshold while confinement near threshold is possible but uncommon.

Abstract

The input power requirements for accessing H-mode at low density and maintaining it during the density ramp in ITER is addressed by statistical means applied to the international H-mode threshold power database. Following the recent addition of new data, the improvement of existing data and the improvement of selection criteria, a revised scaling law that describes the threshold power required to obtain an L-mode to H-mode transition is presented. Predictions for ITER give a threshold power of ∼52MW in a deuterium plasma at a line average density, ne = 0.5×1020m-3. At the nominal ITER H-mode density, ne = 1.0×1020m-3, the threshold power required is ∼86MW. Detailed analysis of data from individual devices suggests that the density dependence of the threshold power might increase with the plasma size and the magnetic field. On the other hand, the density at which the threshold power is minimal is found to decrease with the plasma size and increase with magnetic field. The influence of these effects on the accessibility of the H-mode regime in ITER plasmas is discussed. Analyses of the confinement database show that, in present day devices, H-modes are generally maintained with powers exceeding the threshold power by a factor larger than 1.5, and that, on the other hand, good confinement can be obtained close to the threshold power although rarely demonstrated.