Transport in JET high performance plasmas

Two types of high performance scenario have been produced in JET during the DTE1 campaign. One of them, the ELM free hot ion H mode scenario, which is well known and has been extensively used in the past, has two distinct regions: the plasma core and the edge transport barrier. The results obtained during the DTE1 campaign with D, DT and pure T plasmas confirm the JET Teamʹs previous conclusion that the core transport scales as a gyro-Bohm in the inner half of the plasma volume, recovers its Bohm type nature closer to the separatrix and behaves as neoclassical ion transport in the transport barrier. Measurements on the top of the barrier suggest that the width of the barrier is dependent on isotope and that fast ions play a key role. The other high performance scenario is a relatively recently developed optimized magnetic shear scenario with small or slightly negative magnetic shear in the plasma core. Different mechanisms of internal transport barrier (ITB) formation were tested by predictive modelling and the results compared with experimentally observed phenomena. The observed non-penetration of heavy impurities through the strong ITB, which contradicts a prediction of the conventional neoclassical theory, is discussed.