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 (ITB), R ∼ 3.7 m, are formed at ITER relevant triangularity δ ∼ 0.45, with ne/nG ∼ 60% and ELMs (edge localized modes) moderated by Ne injection. At higher current (IP ≤ 3.5 MA, δ 0.25) wide ITBs sitting at R ≥ 3.5 m (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 are obtained with plasma target preformed by opportune timing of LHCD (lower hybrid current drive), pellet injection and small amount of NBI (neutral beam injection) power. ITB starts with toroidal rotation 4 times lower than the standard NBI heated ITBs. Full CD (current drive) is achieved in reversed shear ITBs at 3 T / 1.8 MA, by using 10 MW NBI, 5 MW ICRH and 3 MW LH. Wide ITBs located at R = 3.6 m, without impurity accumulation and type-III ELMs edge can be sustained for a time close to neo-classical resistive time. These discharges have been extended to the maximum duration allowed by subsystems (20 s) with the JET record of injected energy: E ∼ 330 MJ. Integrated control of pressure and current profiles is an essential feature used in these discharges. Central ICRF mode conversion electron heating, added to about 14 MW NBI power, produced impressive ITBs with equivalent QDT ∼ 0.25. Conversely ion ITBs are obtained with low torque injection, by ICRH He3 minority heating of ions, on pure LHCD electron ITBs. Similarity experiments between JET and AUG have compared the dynamics of ITBs and have been the starting point of Hybrid Scenarios activity, then developed at ρ* as low as ρ* ∼ 3*10-3. The development of hybrid regime with dominant electron heating has also started. Injection of trace of tritium and a mixture of Ar/Ne allowed studying fuel and impurities transport in many of the explored advanced tokamak scenarios. (authors)