JET and the Road to ITER

JET experimental results directly relevant to ITER design are presented. From recent experiments in DT mixtures varying from 100:0 to 10:90, it is inferred that an inverse mass dependence should be included in the H-mode power threshold scaling. Using ITER similarity experiments, the global energy confinement time in JET discharges with type I ELMs is found to be consistent with the gyro-Bohm physics form which has no dependence on plasma β. This form has a weak negative mass dependence but a stronger density dependence than the ITERH93-P scaling. Using the JET MkIIa pumped divertor with N₂ seeding, ITER-relevant highly radiative regimes (P_R up to 75%) accompanied by type III ELMs have been studied. It is found that the confinement degrades progressively with increasing radiative power fraction. Power loading of divertor tiles with type I ELMs appears to be excessive with NBI whereas it is less of a concern with ICRH. Preliminary assessement of the ITER reference second harmonic (2ɷCT) ICRH scenario with and without the addition of a small amount of He3 is also presented. High performance optimised shear discharges with potentially ‘well aligned’ bootstrap current scenarios consistent with ITER-relevant steady-state operation have also been studied. Internal transport barriers featuring peaked plasma profiles have been demonstrated in DT plasmas in JET. Preliminary results of α-particle driven toroidal Alfven eigenmodes (TAEs) in the ‘after-glow’ of NBI heated 50:50 DT plasmas are also presented.