SUMMARY

The divertor is a key plasma-facing component of future magnetic fusion energy reactors, helping to sustain fusion reactions by removing helium ash and impurities from the core plasma. The divertor target plates are therefore subject to steady-state incident heat fluxes of at least 10 MW/m^2. The helium-cooled modular divertor with multiple jets (HEMJ), which uses 25 impinging jets of helium to cool the plasma-facing tungsten tiles, is a leading candidate for the proposed international fusion reactor DEMO. Experiments were performed on a single HEMJ module to characterize its thermal-hydraulics at coolant inlet temperatures up to 425 °C, inlet pressures of 10 MPa, and incident heat fluxes up to 6.6 MW/m^2 using a helium loop for mass flow rates up to 10 g/s. The effect of varying the jets impingement distance from 0.5 mm to 1.5 mm was investigated. The data were used to develop correlations for the average Nusselt number over the cooled surface and loss coefficient, which were then used to develop parametric design charts that predict performance at prototypical inlet temperatures of 600 °C and heat fluxes of 10 MW/m^2. A numerical model was developed using commercial software, and validated by experimental data. The model was used to study the thermo-mechanical performance of the HEMJ at prototypical conditions, and estimate thermally-induced stresses and deformation. The results suggest that the HEMJ can accommodate 10 MW/m^2 while keeping pumping power requirements within reasonable limits. Numerical simulations were also performed to optimize the divertor geometry; based on these numerical optimizations, a simplified design, which could reduce manufacturing costs for the large number (O(10^6)) of modules required, was fabricated and tested in the helium loop. This variant can accommodate 8 MW/m^2 at prototypical conditions.