Ion gyro orbit heat load simulations on real CAD using open source software

Accurate and precise heat load predictions are critical to ensuring that plasma facing component (PFC) designs meet performance targets in high power density tokamaks. Recently, the open source Heat flux Engineering Analysis Toolkit (HEAT) was developed to compute time-evolving PFC heat loads incident upon fully featured 3D PFC CAD geometries. Up until now, HEAT has simulated heat loads under the 'optical approximation' - the assumption that heat is transported directly along the magnetic field lines. In reality, particles follow helical 'gyro orbit' trajectories as they precess about the magnetic field lines at finite Larmor radii. Including the effects of gyro orbit trajectories in the heat load calculations can result in deviations from the optical approximation for the ion heat flux, as particles can access regions that are magnetically shadowed from straight field line fluxes. This effect is increased during transients such as ELMs where free streaming of ions at the pedestal temperature can increase the radius. A new HEAT module has been developed that enables users to calculate gyro orbit heat loads. A side by side comparison between optical and gyro orbit results will be presented using castellated tile geometries for the NSTX-U divertor.