Neoclassical transport analysis of titanium impurity in plasmas with strongly peaked density profiles

The full neoclassical multi-ion calculation required for the interaction between titanium and light impurities like carbon and oxygen is presented. Intrinsic titanium impurity behavior in pellet fuelled plasmas was studied by applying the neoclassical impurity transport calculation to temporal evolutions of Ti XX and Ti XXI spectroscopically observed. Ti impurity accumulates in the plasma core region, correlated with peaked density profile and the absence of sawtooth oscillation. Impurity accumulation is caused by a strong ion density gradient driving force and collisions with light impurities, as the neoclassical impurity transport theory predicts. This impurity behavior is well described by the combination of reduced anomalous diffusion and neoclassical transport in the plasma interior. The reduced anomalous diffusion at the central region inside the q=1 is estimated to be 0.2 m2/s. The outer zones continue to be dominated by anomalous transport. (author)