T-rich scenario for the record fusion energy plasma in JET DT

One of the main goals of the recent JET DT experimental campaign with ITER-like wall was to achieve high fusion power >10MW steady for 5 seconds. Scenarios developed for that purpose were utilizing close to 50/50 DT plasma mixture and balanced D-NBI and T-NBI injected heating power.

A different route to achieve this goal used D-NBI heating into a tritium plasma to maximize the number of beam-target D-T reactions. This was predicted to produce higher net fusion power in comparison to 50/50 DT plasmas of similar performance. Providing low deuterium concentration in such a plasma, it could also be combined with fundamental D-minority ICRH for additional boost to the fusion power. At JET, this scheme is accessible at the lowest ICRH frequency 29MHz and high BT=3.86T which is an engineering limit for 5s flattop plasma.

A mock up experiment with D-NBI heating of hydrogen plasma was performed prior to the DT campaign to test the isotope control aspect. 15/85 DH composition was readily achieved without excessive core accumulation of deuterium despite intensive core fuelling by NBI particles. That confirmed the fast isotope mixing effect previously observed at JET albeit at lower plasma current and heating power.

Subsequently, a stable hybrid scenario pure tritium plasma with T-NBI was demonstrated and served as a reference discharge for the DT. After a few minor modifications this plasma was finally performed with D-NBI and 29MHz ICRH to produce a series of record fusion energy pulses, with the highest E_fus=59MJ and 5s-averaged Q=0.33. As expected, the plasma remained Tritium-rich with approximately 15/85 DT composition. Somewhat surprisingly, this plasma had rather small and fast (80-100Hz) ELMs, despite the high tritium content and high additional heating power injected.

In this contribution, the main experimental results related to the record fusion energy pulse will be shown, together with the first analysis and modelling.