Ion orbital behavior in diverted tokamak geometries

Ion particle transport in diverted tokamak geometries is investigated employing analytical models for the equilibrium magnetic field. In the presence of magnetic stochasticity, magnetic field lines inside the separatrix can be connected to the open magnetic field line regions. After crossing the separatrix, passing particles can easily reach the divertor plates within finite toroidal evolutions while trapped particles persist due to conservation of second adiabatic invariant. Interestingly, a steady state H-mode is sustained with RMPs [T.E.Evans, R.A.Moyer et al., Nature Phys. 2, 419 (2006).] even in the presence of an enhanced ion particle loss. Global plasma profiles and distribution function at the steady state with the RMPs is computed. The computational model is also applied to study ion transport in negative triangularity tokamaks. While they are expected to reduce the heat flux because of the larger major radius (at the radius where the separatrix crosses the divertor plates), radial extent of the particle deposition can be localized due to small magnetic drifts at the outboard side which has nearly a vertical shape. Computation of heat loads on the divertor plates, with an optimized magnetic configuration is discussed.