Description
The experiments performed at the Joint European Torus (JET) in the final years of operation give the unique opportunity to investigate future reactor relevant issues. In preparation to the second deuterium–tritium campaign (DTE2) JET team developed a high-current baseline scenario capable of sustaining high performance for 5 s. The scenario was developed in D plasmas through a stepwise increase in plasma current (2.5-4.0 MA), optimised for high performance and repeatability, while minimising particle throughput. However, when reproduced in T and D-T mixtures, with Ip=3.5 MA and BT=3.3 T, the discharge duration was limited to 2–3 s due to weakened ELM activity.
The modelling presented starts from predictive core simulations of these D, T and D-T pulses, performed with JINTRAC equipped with the reduced first-principle based transport model QuaLiKiz. Plasma kinetic profiles, core performance as well as the isotope mixture are well reproduced with a realistic impurity mixture of beryllium, nickel and tungsten. Using COCONUT we extend the simulation domain from core-pedestal to the Scrape-off layer imposing the nominal gas puffing throughput to investigate the role of fuelling in achieving a 50-50 D-T mixture via T gas, D pellets, and neutral beam injection. We are presenting a novel framework of validation with the state-of-the-art models that are being used in ITER re-baselining with D-T isotope segregation and impurities (including W). COCONUT modelling results across isotope mixtures reveal a reduction of core ionisation sources in T and D-T (particularly at low particle throughput) consistent with the experimentally observed weakened ELM activity. Moreover, experiments performed during DTE3 confirmed within the same plasma scenario the possibility of sustaining the pulse in D-T with higher gas puff nominal throughput. Despite the critical importance of density and fuel mix control for future devices, these aspects remain only sporadically explored due to large uncertainties in edge particle sources. The JET baseline scenario offers a unique opportunity to address these ITER relevant conditions (e.g. small compound ELMs, competition between pellet and gas puffing), as it employs multiple fuelling channels with different isotopes, enabling the measured isotope ratio to serve as a constraint for the analysis.