Numerical study of limits of neoclassical theory in the plateau regime in the presence of impurities

This paper presents a numerical simulation to test the corrections to the radial electric field in the presence of impurities for tokamak devices whose main ions are in the plateau regime. The effects due to the presence of impurity density variation in a pedestal tokamak are known to generate conditions where conventional neoclassical theory is no longer valid. It is found that for a specific axisymmetric concentric magnetic field, the presence of steep radial gradients for both temperature and density translates in a correction to the radial electric field. We anticipate that comparisons to the Landreman–Fülöp–Guszejnov model display good agreement for both the analytic approximation and numerically solved value of the normalized density when low impurity concentration and atomic charge state cases are considered, coupled with values of the ordering parameter (Formula presented.). Higher values of the latter reveal better agreement to the neoclassical Hazeltine–Hinton formula, suggesting a discrepancy with the validity threshold of the model.