Radiative power loading in the ITER divertor

In ITER, steady state burning plasma operation will require a partially detached divertor state in order to reduce the peak power flux density to technologically achievable values at the actively cooled target plates (∼10 MW m−2). Such partially detached solutions require high radiative power dissipation in the divertor volume, with 60–70 MW expected in the baseline H-mode operating scenario. Power levels of this magnitude pose potential difficulties for divertor substructures, which, although also actively cooled, are not designed to withstand very high heat fluxes. This paper estimates the radiative power flux densities falling on critical divertor substructures during ITER burning plasma operation using commercial optical ray-tracing software to project radiation distributions simulated with the SOLPS plasma boundary simulation code onto a full 3D description of the divertor. The results indicate that inclusion of the real geometry provides heat flux densities due to photon illumination not higher than quasi-analytic estimates used in the original divertor design stages, and in some cases lower. When applied to the specific simple geometries used to develop the analytic expressions, the raytracing fully validates the analytic approach.