Impurity dynamics in plasma turbulence: multiscale analysis, intermittency, and non-diffusive transport

Impurity transport in tokamak plasmas is investigated using a three-dimensional fluid global code. The impurities are treated as an active scalar and the self-consistent interaction between the impurity concentration and the turbulence is studied in detail. A multiscale analysis based on proper orthogonal decomposition methods reveals that the impurity concentration gives rise to strong intermittency in the ${\bf E} \times {\bf B}$ flow and the ion temperature flux. The probability density functions of fluctuations exhibit a transition from Gaussian (for low Z impurities) to exponential (for high Z impurities). Spatio-temporal flux-gradient cross correlation functions are used to characterize the level of non-diffusive, non-local transport in the system.