Isotope scaling of the H mode power threshold on JET

TLDR

The study investigates how the H‑mode power threshold depends on plasma isotopic mass using experiments on JET with tritium, DT, deuterium, and hydrogen plasmas. The experiments measured the H‑mode threshold and, for some discharges, pedestal electron and ion temperatures to assess the influence of isotopic mass on the critical edge temperature. The H‑mode threshold scales as \(P_{\text{thr}}\propto A_{\text{eff}}^{-1}\) across the isotopic range, implying a 20 % power reduction for a 50:50 DT reactor compared to a DD mixture, and the power needed for the type I ELM transition also follows this scaling.

Abstract

Results are presented from a series of dedicated experiments carried out on JET in tritium, DT, deuterium and hydrogen plasmas to determine the dependence of the H mode power threshold on the plasma isotopic mass. The Pthr ∝ Aeff-1 scaling is established over the whole isotopic range. This result makes it possible for a fusion reactor with a 50:50 DT mixture to access the H mode regime with about 20% less power than that needed in a DD mixture. Results on the first systematic measurements of the power necessary for the transition of the plasma to the type I ELM regime, which occurs after the transition to H mode, are also in agreement with the Aeff-1 scaling. For a subset of discharges, measurements of Te and Ti at the top of the profile pedestal have been obtained, indicating a weak influence of the isotopic mass on the critical edge temperature thought to be necessary for the H mode transition.