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.

Oxygen impurity transport in the typical discharges of the Aditya tokamak was investigated using emissivity radial profile of emissivity of the spectral line (2p3p ³D₃–2p3d ³F₄) at 650.024 nm from the Be-like oxygen ion. This O⁴⁺ spectral line was recorded using a 1.0 m multi-track spectrometer capable of simultaneous measurements from eight lines of sight passing through the plasma. The oxygen transport coefficients were determined by reproducing the experimentally measured emissivity profiles of O⁴⁺, using a one-dimensional impurity transport code, STRAHL, and photon emissivity coefficient (PEC) belonging to that transition. The PEC values were obtained from both ADAS and NIFS atomic databases. Using both the databases, much higher values of diffusion coefficients compared to the neo-classical values were observed in both high and low magnetic field edge regions of typical Aditya tokamak Ohmic plasma. Although, almost similar profiles of diffusion coefficients were obtained using PEC values from both databases, the magnitude differs considerably. The maximum values of diffusion coefficients in the plasma edge at low field side of tokamak were ~45 and ~25 m²·s⁻¹ when modeling was done using the ADAS and NIFS databases, respectively. Further analysis on the atomic data used in the calculation indicates that the difference in diffusion coefficients is mainly related to the variation in the values of atomic data of the two databases.

The present study is an analysis between radial emissivity profiles of the 650.024 nm transition of the O4+ ion obtained using two separate Photon Emissivity Coefficient (PEC) databases. Emissivity values of the 650.024 nm O4+ transition in visible-spectral region have been experimentally obtained for the Aditya tokamak. The radial number density distributions of different charge states of oxygen are estimated using a semi-implicit numerical method applied over the radial impurity transport equation. The 650.024 nm emissivity is calculated using the obtained impurity number density and with PECs from two separate databases namely the ADAS (Atomic Data and Analysis Structure) and the NIFS (National Institute for Fusion Science) database. Although impurity diffusivity profiles must not be dependent upon the choice of PEC databases; yet a requirement of separate impurity (oxygen) diffusivity profiles for the two PEC databases is observed, such that their corresponding calculated O4+ emissivities best depict the experimental emissivity data. A difference in the ionization and recombination rate coefficients provided in the ADAS and NIFS databases can lead to discrepancies in the impurity number densities calculated. The effects upon the impurity diffusivity while using ionization and recombination rate coefficients from two separate databases are further studied.