Description
The study here shows the effects of shape optimization parameters such as plasma triangularity (δ) on anomalous transport of impurity species within high density L-mode spherical tokamak plasmas. Impurities are non-fuel species within plasma that can hinder the confinement by means of radiation losses or fuel dilution and therefore prevent a long-pulse sustenance. The impurity element analyzed here is the low Z carbon (C, Z = 6). Theoretical design of a spherical tokamak (ST) configuration is used for simulating varying triangularity steady-state plasma conditions within them using the open-source Grad-Shafranov equation solver FreeGS. While the theoretical ST design shown here does not belong to any current operational systems, the design parameters and the parameters characterizing the plasmas simulated within them are in accordance with the existing ST systems worldwide. Shape optimization parameters influence the kinetic (parameter) profile distributions within plasmas which in turn influence the type of microinstability that may dominate at a given region of a plasma. Effects from impurity transport on such microinstabilities in varying triangularity, high-density plasmas are analysed in this study using the gyro-kinetic code GENE. Analyses shown here based on GENE results of the FreeGS simulated plasmas provide with insights regarding first, the effects of change in δ on impurity distribution(s) within a plasma and second, whether such change in impurity distribution(s) influence the nature of local microturbulences.