Stellarator Impurity STRAHL Code Development in NIFS

Abstract

The new Stellarator Impurity Transport (SIT) code is an extended version of STRAHL code [1], which can be used for non-axisymmertic magnetic configurations to evaluate impurity behavior in the frame of the stellarator-specific neoclassical transport, which is strongly dependent on magnetic topology and the radial electric field. The code solves the system of 1D continuity equations (averaged over the magnetic flux surfaces) for impurity ions of each charge state, coupled due to the ionization and recombination. It calculates the time and space evolution of density and emission of impurity ions coming from the wall or deposited within the plasma during the pellet ablation. An analytical description of the neoclassical transport coefficient for the background plasmas was generalized to impurity ions of arbitrary mass and charge state and used in the code as a neoclassical transport model for impurities. Calculations of the electric field and transport coefficients are included within the time dependent iterative loop. Various models of anomalous drift velocities and diffusion coefficients were incorporated. The code can be used as an interpretative and predictive tool for simulation of impurity behavior in arbitrary non-axisymmetric configurations.