Numerical estimation of the oxygen impurity transport in the Aditya tokamak

Abstract

The present study illustrates an approach to solving the one-dimensional impurity transport equation in tokamak plasma, without the loss of generality, using a semi-implicit numerical method. The radial profiles of number density distribution of different ionization states of oxygen (Z = 1 to Z = 8) have been estimated using the ionization and recombination rate coefficient data from the Atomic Data and Analysis Structure database. The rate coefficients are determined based on the electron temperature and number density distribution in the Aditya tokamak. The radial number density profile of the O4+ ion, obtained using the semi-implicit impurity transport equation, has been applied further in determining the radial emissivity profiles of the characteristic 650.024 nm transition of the Be-like O4+ ion. The simulated O4+ emissivity is then matched with respect to the experimental emissivity values along inboard (high toroidal magnetic field) and outboard (low toroidal magnetic field) regions of the Aditya tokamak. The comparison estimates the nature of the radial diffusivity profile of oxygen ions, which in turn demonstrates the nature of oxygen transport in Aditya plasma. Large values of oxygen ion diffusivity (> neo-classical values) are observed toward the plasma edge in both regions of the Aditya tokamak. These diffusivity values point toward a fluctuation induced transport in the edge region of Aditya plasma. The simulated results are benchmarked with the STRAHL code. The semi-implicit form of the radial impurity transport equation can be extended to deduce the distributions of other light impurities in tokamak plasma.