Optimization of the thermal-hydraulic performance of the helium-cooled modular divertor with multiple jets
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The divertor is a key plasma-facing component of future commercial magnetic fusion energy (MFE) reactors that helps sustain fusion reactions by removing helium ash particles and impurities from the core plasma. The divertor target plates are therefore subject to high steady-state incident heat fluxes, expected to be at least 10 MW/m^2 in the international demonstration (DEMO) fusion reactor. The helium-cooled modular divertor with multiple jets (HEMJ), which uses 25 impinging jets of helium to cool plasma-facing tungsten tiles, is a leading candidate for DEMO. Experiments were performed on a single HEMJ module to characterize its thermal-hydraulic performance 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 closed helium loop. The effect of the jets-to-impingement surface separation distance was experimentally investigated. A numerical model was developed with a commercial software package, and validated against experimental data. The model was used to evaluate the thermo-mechanical performance of the HEMJ, and to optimize the divertor geometry toward a design that is more favorable to fabricate. The optimized HEMJ variant was fabricated and tested in the helium loop. The experimental results were used to develop parametric design charts that predict the HEMJ thermal performance at prototypical inlet temperatures of 600 °C and heat fluxes of 10 MW/m^2. The simulation results provide estimates of thermally-induced stresses and expansion. The results suggest that the HEMJ can accommodate 10 MW/m^2 while keeping the pumping power requirements within specified limits. The simpler HEMJ variant can accommodate 8 MW/m^2 under the same conditions, which could simplify manufacturing and reduce fabrication costs for O(10^6) modules.