On the possibility of determining the sawtooth location from impurity ion density profiles

Abstract

A new method is proposed for determination of the magnetic island location from the density profiles of multiply charged impurity ions. The method is based on (1) measuring the impurity ion’s emissivity profiles in T-10 tokamak experiments and (2) a theoretical model for the behavior of the impurities under conditions of sawtooth oscillations. The main physical basis of the method is the fact that the impurity is forced out from the sawtooth region in such a way that the profile of impurity ions appears to be a composition of two different profiles. These two profiles are determined by the Braginskii mechanism of impurity diffusion sustained in the regions r≳rs and r<(rs−Δ), whereas in the transient region (rs−Δ)≤r≤rs the impurity density has a sharp drop with decreasing minor radius. Interpretation of T-10 tokamak experimental data within the frame of a theoretical model allows one to determine the location of the surface q=1 and the width of magnetic islands. The method appears to be very sensitive to the level of large-scale MHD activity of the plasma.