Development on JET of advanced tokamak operations for ITER

Recent research on advanced tokamak in JET has focused on scenarios with both monotonic and reversed shear q -profiles having plasma parameters as relevant as possible for extrapolation to ITER. Wide internal transport barriers (ITBs), r / a ∼ 0.7, are formed at ITER relevant triangularity δ ∼ 0.45 and moderate plasma current, I P = 1.5–2.5 MA, with n e / n G ∼ 60% when ELMs are moderated by Ne injection. At higher current ( I P ≤ 3.5 MA, δ ∼ 0.25) wide ITBs sitting at r / a ≥ 0.5, in the positive shear region, have been developed. Generally MHD events terminate these barriers otherwise limited in strength by power availability. ITBs with core density close to Greenwald value, T e ∼ T i and low toroidal rotation (4 times lower than standard ITBs) are obtained in plasma target preformed by opportune timing of lower hybrid current drive (LHCD), pellet injection and a small amount of NBI power. Wide ITBs, r / a ∼ 0.6, of moderate strength, can be sustained without impurities accumulation for a time close to neoclassical resistive time in 3 T/1.8 MA discharges that exhibit reversed magnetic shear profiles and type-III ELMy edge. These discharges have been extended to the maximum duration allowed by JET subsystems (20 s) bringing to the record of injected energy in a JET discharge: E ∼ 330 MJ. Portability of ITB physics has been addressed through dedicated similarity experiments. The ITB is identified as a layer of reduced diffusivity studying the propagation of the heat wave generated by modulating the ICRF mode conversion (MC) electron heating. Impressive results, Q DT ∼ 0.25, are obtained in these deuterium discharges with 3 He minority when the MC layer is located in the core. The ion behaviour has been investigated in pure LHCD electron ITBs optimizing the 3 He minority concentration for direct ion heating. Preliminary results of particle transport, studied via injection of a trace of tritium and an Ar–Ne mixture, will be presented.