(TH/P8-38) Non-local Models of Perturbative Transport: Numerical Results and Application to JET Experiments
1) Oak Ridge National Laboratory, Oak Ridge, TN, United States of America
2) Istituto di Fisica del Plasma, Associazione Euratom-ENEA-CNR, Milano, Italy
3) Association EURATOM - Risoe National Laboratory Technical University of Denmark, Denmark
Abstract. Perturbative experiments in fusion plasmas have shown that edge cold pulses travel to the center of the device on a time scale much faster than expected on the basis of diffusive transport. An open issue is whether the observed fast pulse propagation is due to non-local transport mechanisms or if it could be explained on the basis of local transport models. To elucidate this distinction, perturbative experiments involving ICRH power modulation in addition to cold pulses have been conducted in JET for the same plasma. Local transport models have found problematic to reconcile the fast propagation of the cold pulses with the comparatively slower propagation of the heat waves generated by power modulation. In this paper, a non-local model based on the use of fractional diffusion operators is used to describe these experiments. The proposed non-local model is able to reproduce the profiles of the amplitude and the phase of the dominant harmonics of the electron temperature corresponding to the propagation of heat waves excited by the ICRH modulation in JET. Most importantly, for the same model parameter values, the model can successfully accommodate the propagation of pulses with time delays comparable to those in the experiment, ∼ 4 ms. We also present a detailed numerical study of the parameter dependence of the transport properties of the fractional model. In addition, we present preliminary results on the role of non-locality in the propagation of pulses in the presence of internal transport barriers.
Full paper available (PDF)