Overview of Thermal Hydraulics of Helium-Cooled Solid Divertors

Developing ways to effectively remove the extremely high heat fluxes incident on the plasma-facing components is an important challenge for magnetic fusion energy (MFE). In most cases, the target plates of the divertor, which removes helium ash and other impurities from the core plasma, are subject to the most extreme conditions, with steady-state incident heat fluxes of at least 10 MW/m². Starting from the early 1990s, a variety of divertor designs with target plates of tungsten (W), cooled for the most part by impinging jets of helium (He), have been investigated.

This paper reviews and discusses a number of these impinging-jet concepts, including the modular He-cooled finger-type configurations developed by the Karlsruhe Institute of Technology (KIT), as well as the T-tube divertor, the helium-cooled flat-plate (HCFP) divertor, and the combined plate/finger divertor, all evaluated as part of the ARIES studies. Over the last 15 years, a number of studies have shown that the steady-state thermal and structural performance of single units of a number of these divertor designs can be evaluated with reasonable accuracy under prototypical conditions using a combination of numerical simulations and experimental studies. The helium-cooled modular jet (HEMJ) design has been successfully tested at incident heat fluxes as great as 13 MW/m² at prototypical conditions. Although it remains unclear how much neutron irradiation damage will affect W, or other armor materials, He jet-impingement cooling is a leading candidate for resolving power exhaust heat removal issues in plasma-material interactions.