An Experimental Study of the Helium-Cooled Modular Divertor with Multiple Jets at Nearly Prototypical Conditions

A new helium (He) loop was used to study the helium-cooled modular divertor with multiple jets (HEMJ) at incident heat fluxes q″ ≤ 6.6 MW/m² as part of the joint US-Japan effort on plasma-facing components evaluation by tritium plasma, heat, and neutron irradiation experiments (PHENIX). These studies were performed at prototypical pressures of 10 MPa and inlet temperatures ranging from 30 °C to 300 °C. The effect of varying the distance between the inner jets cartridge and the outer shell from 0.44 to 0.9 mm was also investigated.

The Nusselt number Nu results for two different tungsten-alloy test sections were in good agreement for q″ = 1.5−6.6 MW/m². The experiments also suggest that the loss coefficient K_L is essentially constant. These Nu and K_L results were used to estimate the maximum heat flux q′′_max that can be accommodated by the divertor under prototypical conditions and the coolant pumping power as a fraction of the incident thermal power β. The agreement over the broad range of experimental parameters studied suggests that these results at near-prototypical conditions can be extrapolated with reasonable confidence to the operating conditions expected for the HEMJ design.