Edge Pedestal Deterioration

摘要

A model for calculating edge gradients in density and temperature from transportand atomic physics considerations is combined with a model for calculating the enhancement of edge transport by thermal instabilities, the onset and strength of which in turn depend on edge gradients and atomic physics. A minimum threshold value of the non-radiative power flux passing through the edge that is needed to suppress transport enhancing thermal instabilities and a maximum allowable value of the power flux through the plasma edge are established. When the power flux through the edge is less than this minimum threshold value, the model predicts a deterioration of the edge gradients as the neutral concentration, the impurity concentration and/or the impurity radiation emissivity in the edge plasma increase, which is consistent with experimental observations in many instances. Model problem calculations are presented to illustrate the predicted pedestal deterioration for representative experimental conditions.