High-Recycling Characteristics in the KSTAR Tokamak Divertor by Using Two-Dimensional Transport Simulations

Abstract

The operation space in the conduction-limited divertor regime of the KSTAR (Korea Superconducting Tokamak Advanced Research) tokamak is obtained in terms of the upstream density and the input power through numerical simulations using a two-dimensional two-fluid edge plasma transport code coupled with a two-dimensional Monte Carlo recycling neutral transport code in which the electron impact ionization and the charge exchange of recycling neutrals are taken into account. Two major high-recycling characteristics, the parallel temperature gradient and plasma pressure conservation, are identi ed in this operation space along the magnetic ux tubes between the upstream position and the divertor target plate in the KSTAR tokamak. Inclusion of ion pressures in the present simulations for total plasma pressures shows firm evidence of pressure conservation in the high-recycling regime. In addition, scalings of the plasma temperature and density at the divertor plate with the upstream plasma density are derived, and they are compared with those in a simple one-dimensional analytic transport model, the so-called two-point model. Finally, the simulation shows that the peaked feature of the upstream ion temperature pro le adjacent to the separatrix a ects the distribution of the divertor heat flux. This indicates that the ion parallel heat conduction near the separatrix plays an important role in determining the radial pro le of the heat flux onto the divertor target, as the electron parallel heat conduction does in the conduction-limited regime. It is, therefore, suggested that modification of the upstream plasma property profiles will make it possible to control the power dispersal on the divertor plate.