Reduced model (nSOLT) simulations of neutral-plasma interaction in the edge and SOL: verification, equilibrium profiles and turbulent momentum transport*

The 2D scrape-off-layer turbulence code (SOLT) has been extended to include neutral-plasma interactions (nSOLT). A Boltzmann equation describes the evolution of the bi-normally (y) averaged neutral distribution function, G(x,v_x,t), in the radial dimension. Neutral-plasma interactions are mediated by charge-exchange and ionization rates based on poloidally-averaged plasma density and temperature. As a verification exercise, equilibrium neutral density profiles from nSOLT simulations and from the Monte Carlo neutral transport code DEGAS 2 are compared, for time-averaged NSTX H-mode plasma profiles, and are found to be in good agreement.  nSOLT simulations that evolve the plasma in 1D, using radial diffusion as a proxy for turbulent (blob) transport, illustrate the convergence to self-consistent neutral-plasma equilibria sustained by a neutral source in the far-SOL and plasma heating in the core. In 2D nSOLT turbulence simulations, the effect of neutral friction on the radial transport of injected poloidal plasma momentum is studied. Neutral friction and plasma cooling are compared as modifiers of the plasma flows.