Fundamental ICRF heating of deuterium ions in JET-DTE2

Beam-target reactions are responsible for a substantial fraction of the fusion power generated in D-T plasmas in JET-ILW (Be/W-wall), with ion temperatures of 10-12keV and large neutral-beam injection (NBI) power. It is known that injecting D beam ions with energies of ∼100-150keV in T-rich plasmas has a larger potential for beam-target fusion than in 50:50 D:T plasmas, but such a scenario was never developed in the past D-T experiments performed in JET-C (Carbon-wall) and in TFTR in the 90's. On top of the intrinsic advantages of using D beams in T-rich plasmas for D-T neutron production, simulations have shown that fundamental ion-cyclotron resonance heating (ICRH) of the D ions can significantly boost the net fusion reactivity, since both the thermalized D ions and the fast D-NBI ions are accelerated to energy ranges that are optimal for the D-T reaction cross-section. The beneficial effect of fundamental D ICRH on thermal D minorities in tritium plasmas (without NBI) was identified in the JET-C D-T experiments, but was not tested in high performance H-mode discharges with D-NBI heating. In 2021, dedicated JET-ILW DTE2 [1] experiments confirmed - for the first time - the improved fusion performance of T-rich plasmas with high D-NBI power and highlighted the key impact of fundamental D ICRH on the fusion reactivity. This new scenario lead to the world-wide 5s averaged fusion power (and energy) record in D-T tokamak plasmas with dominant beam-target reactions. A brief experimental overview followed by detailed RF wave / Fokker-Planck simulations including NBI-ICRH synergy will be presented, to disentangle the different components contributing to the high neutron yield achieved in these experiments.