The Effects of Gas Puff Locations on the Symmetry of Divertor Conditions in MAST-U

To mitigate the issue of plasma exhaust in tokamaks double-null (DN) configuration is thought to be advantageous over a single-null (SN) configuration, due to its potential benefits for power exhaust arising from the use of four active divertors and magnetically disconnected low and high-field sides. Different gas puff locations can potentially break the up-down symmetry of heat load on upper and lower divertor targets, which may lead to excessive heat loading of upper or lower divertor target. The effect of different D₂ fueling locations in the MAST-U tokamak is studied in detail with the SOLPS-ITER code to gain insights to detachment conditions in H-mode plasma experiments in conventional divertor configuration. Two fueling locations “Middle” (inner midplane) and “Bottom” (lower outer divertor) were chosen. When the fueling location is changed from Middle to Bottom with the same puffing rate, the peak heat flux density at the lower outer target is reduced by 64% and the peak heat flux density at the outer upper target is increased by 29%. The result demonstrates that a change in the gas puff location can break the symmetry between upper and lower divertors and that an optimized control of the location is beneficial to avoid excessive heat loading on the upper or lower divertor target.