Non-diffusive turbulent transport of impurities in fusion plasmas

Non-diffusive 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. It is shown that the impurity concentration triggers intermittency that gives rise to a transition from Gaussian to stretched-exponential probability density functions of the ${\bf E} \times {\bf B}$ fluctuations. Proper orthogonal decomposition methods are used to unveil the multiscale spatio-temporal dynamics of the impurity concentration, the turbulence fluctuations, and the ion thermal flux. Spatio-temporal flux-gradient cross correlation functions are used to characterize the level of non-diffusive transport in the system. A novel diagnostic based on the use of Fourier-Laplace transforms is proposed and implemented to characterize the level of non-locality in space and time.