Fast Responses of Core Plasma to Dithering ELMs

A non-local transport model is applied to describe the fast propagations of the pulses induced in the edge by dithering Edge Localized Modes (dithering ELMs). A small fraction of non-local component is found to be very eectiv e in modifying the response of the core electron temperature. A phase reversal of the perturbed electron temperature is predicted in the plasma core based on the non-local transport model. I. Introduction The studies of the improved connemen t have been developed extensively. Although the ELMy H-mode is one of the improved connemen t modes and is considered as a candidate for ITER’s operational scenario, the inuence of the dithering ELMs on the plasma core connemen t has not been fully understood yet. Transient responses in high temperature plasmas have been studied in a lot of fusion devices [1] to investigate the transport mechanism. Recent experiments on transient transport have shown that the eectiv e heat diusivit y seems to change much faster than the change of the local plasma parameter. The pulses are triggered not only at the plasma core but also plasma edge. They are induced at the plasma center both externally by the heating power switching [2] and heating power modulation [3], and spontaneously by the sawtooth crash [4]. Also, they are induced at the plasma edge both externally by impurity injection [5] and spontaneously through L/H (H/L) transition [6] and ELMs [7]. It has been observed in W7-AS that when the periodic heat pulses are induced at the core plasma by the heating power modulation, the phase of the Fourier-decomposed perturbation of the electron temperature is reversed at the plasma edge [3]. This phenomenon, i.e., the phase reversal, has been explained by the non-local transport model [8], in which it is assumed that the plasma has a long range radial correlation. This model has been also applied to the power switching experiment [8], L/H (H/L) transition [9, 10] and impurity injection [11], and successfully explained the fast responses of the heat ux and electron temperature. If the plasma has a long range radial correlation, the similar phase reversal is expected to appear at the plasma core when the dithering ELMs occur at the plasma edge. In this paper, we apply the non-local model to the dithering ELMs and study the response of the electron temperature. The fast response in the core plasma is obtained and phase reversal of the perturbed electron temperature is predicted. II. Non-local Transport Model In this section, we present our model and explain its properties. To investigate the transient response of the electron temperature, let us start with the transport equation for the electron temperature, @ @t