FIREFLY: heat load and particle exhaust approximations for rapid evaluation of divertor designs

Abstract The divertor in a magnetic confinement fusion reactor is an essential
component for power dissipation and particle removal. This article introduces the
FIREFLY package for rapid evaluation of divertor designs based on an extension of
the FLARE code for field line reconstruction from an unstructured flux tube mesh. First, divertor heat
loads are approximated with a simplified heat transport model. Neutralized particles
are then sampled from the resulting distribution, and the EIRENE code is used to
track molecules and atoms in a plasma background while accounting for dissociation,
charge exchange and ionization. Particles are removed on pumping surfaces in order
to estimate the exhaust efficiency for a given divertor geometry. Optimization of the
divertor geometry for more efficient particle exhaust is explored by using W7-X as an
example, and the sensitivity to model parameters for the plasma background in the
proxy calculations is evaluated.