A new collision module for predicting divertor heat flux in axisymmetric discharges*

Particles in fusion plasmas carry immense heat flux to the divertor targets in tokamak fusion devices. In future tokamaks, including ITER, this heat flux is predicted to exceed the limits of the chosen material, tungsten. Predicting the heat flux distribution is a goal of active research for current and future devices. A model was developed (Wingen, et al 2021 Nucl. Fusion 61 016018) based on an ion and electron guiding center drift approximation to simulate convective heat flux in perturbed plasmas. The model focuses on non-axisymmetric, perturbed plasmas, neglecting inter particle collisions. For this reason, the model does not reproduce the correct divertor heat flux profile, an Eich profile (Eich, et al 2011 Phys. Rev. Lett. 107 215001), in an unperturbed axisymmetric case. A collision module has been developed in the MAFOT orbit tracing code that allows for collisional particle transport across the separatrix. Using this module, the divertor heat flux profile for an axisymmetric discharge will be simulated and compared to an Eich profile. The heat flux layer width will be determined and compared with experimental observations from the DIII-D tokamak.