Design of 3D plasma facing components using the DIV3D code

The DIV3D code calculates heat fluxes to plasma facing components (PFCs) in 3D geometry, and has been used to design components for the W7-X stellarator. DIV3D traces magnetic field lines with diffusion determined by a user-specified diffusivity which can be related to the cross-field thermal conductivity and the parallel sound speed. The field lines are initiated on a closed flux surface for which the power density can be specified. In this way, the code essentially models parallel heat convection with cross-field diffusion, appropriate for scrape off layer transport without dissipation. The code has recently been applied to study PFC designs for the DIII-D tokamak and stellarator private industry concepts, and results have shown agreement with experimental data and EMC3 simulations. The code accepts magnetic field data from a number of tokamak and stellarator magnetic equilibrium codes, from coil filaments, and on a general 3D grid of field data. In addition to computing the intersection points and heat flux density, the code can return flux bundle data which can aid in the design of divertor and limiter components. The code has recently been improved for more efficient computation for tokamak applications, leading to a 30x speed up (40% in stellarators). Further advances include the use of two diffusivity values to model both near- and far- SOLtransport to better match experimental data, and the specification of the poloidal distribution of heat on the closed flux surface, e.g. to mimic ballooning transport.