Effects of nitrogen seeding in a tokamak plasma

Abstract

The effects of nitrogen gas seeding in the edge and scrape-off layer (SOL) regions of a tokamak plasma are studied through 2D fluid simulations using the BOUT++ code. Proper account is taken of the presence of multiple charged states of nitrogen ions due to ionization, recombination, and dissociation processes, and a self-consistent study of the interaction of these ions with the turbulent plasma in the edge and SOL regions is carried out. The self-consistent model includes the effects of polarization drifts of the main plasma and impurity ions for determining the plasma vorticity. Nitrogen seeding is found to modify the turbulence as well as to influence the profiles of the equilibrium plasma density and the electron temperature. The densities of N3+ to N5+ ions are found to be relatively higher than the other charged states. This is understood and further validated by a 0D simulation. The radial profiles of these impurity ions are mapped, and their radiation energy losses are estimated. The radial profile of the radiation losses is maximum near to the edge-to-SOL transition region and becomes broader in the edge region than the SOL region.