Modeling of nano-meter scale dust grains in tokamak*

In this work, the NDS (Nano-meter Dust Simulation), which evaluates the charging and ablation processes of the dust grains, has been done under BOUT++ framework. The guiding-center orbits of dust particles are tracked in tokamak plasmas, whose parameters are obtained from BOUT++, a highly desirable C++ code package for performing parallel plasma fluid simulations with an arbitrary number of equations in 3D curvilinear coordinates. The Hamiltonian guiding center equation of motion is utilized to describe the velocity and acceleration of dust grains at arbitrary time step. Calculations with the coupled NDS-BOUT++ codes provide results such as trajectories and distributions of dust particles with different components, sizes, and velocities for different tokamak geometries. The distribution of tungsten impurity, resulted from ablated tungsten dust grains for several typical scenarios, is also assessed. Preliminary results show in some cases, tungsten dust grains can cross the seperatrix and survive for several ms before ablated completely, which will significantly contribute to core contamination.