The tokamak plasma edge for a high confinement mode (H-mode) forms a pedestal structure which leads to favorable boundary conditions for the core plasma region. The success of the International Thermonuclear Experimental Reactor (ITER) is dependent upon the achievability of H-mode operation with a sufficient edge pedestal. The associated behavior is not only dependent on the edge turbulence physics but also on the collisional (“neoclassical”) physics. Many experiments have demonstrated the critical importance of the edge neoclassical dynamics in the open field-line (scrape-off) and pedestal regions, as well as the neutral particle dynamics there. The study of neoclassical physics in the edge region is particularly difficult due to the existence of the combination of a magnetic separatrix with an X-point, open field lines in the scrape-off layer, and a steep plasma gradient -- all of which contribute to breaking the conventional neoclassical orderings. In the present work [as part of the SciDAC Prototype FSP, Center for Plasma Edge Simulation (CEPS)], we have obtained neoclassical solutions in the pedestal and scrape-off region for the first time, using a 5-D gyrokinetic particle simulation code (XGC). Particles are moved in a cylindrical coordinate system consistent with the particle dynamics at the plasma edge, and a field-line tracking mesh is used to study the physics. Both ions and electrons are modeled with the full distribution function of marker particles. The inner radial boundary of the simulation domain is set at a core-edge boundary and the outer boundary is the material wall. The heat flux from the core and the neutral recycling flux from the wall define the particle and energy sources. A significant variation of the electrostatic potential and the pressure along the field line is observed in the open field line region, as anticipated. The ion particle distribution is highly non-Maxwellian. Other findings include: (1) the importance of ExB sheared flow on the plasma flow and the first wall heat load; (2) neutral penetration and ionization effects on the pedestal growth; (3) the role of magnetic field ripple on the pedestal physics; and (4) the plasma rotation generation in the pedestal and scrape-off region. Limited results on edge electrostatic turbulence solutions, self-consistent with the neoclassical physics, will also be presented.
1 SciDAC Fusion Simulation Project Proto-type Center for Plasma Edge Simulation