The effects of gas puff locations and divertor closure on detachment conditions in MAST-U

Abstract The effect of different D 2 fueling locations and divertor closure on MAST-U is studied in detail with the SOLPS-ITER code to gain insights into detachment physics of H-mode plasma experiments in conventional divertor configuration. The SOLPS-ITER simulations reveals that changing D 2 fueling location significantly impacts divertor conditions: Under lower divertor (LD) fueling, the total power loss at the lower outer divertor (LOD) is higher compared to the midplane fueling scenario for the same electron density at the outboard midplane side ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msubsup> <mml:mi>n</mml:mi> <mml:mrow> <mml:mi mathvariant="normal">e</mml:mi> <mml:mo>,</mml:mo> <mml:mi>sep</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>OMP</mml:mi> </mml:mrow> </mml:msubsup> </mml:mrow> </mml:math> ). With LD fueling in closed configuration, the analysis demonstrates substantial reductions on the peak heat flux and electron temperature at the LOD, facilitating the detachment onset due to an increased D neutral density and enhanced radiation, while suppressing carbon (C) sputtering. The closed divertor shows higher neutral trapping capability under both midplane and LD fueling. With LD fueling, the peak plasma temperature ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>T</mml:mi> <mml:mrow> <mml:mi mathvariant="normal">e</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> ) show greater reduction in the closed divertor compared to the open divertor and the roll over of main ion flux ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi mathvariant="normal">Γ</mml:mi> <mml:mrow> <mml:mi mathvariant="normal">i</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> ) happens at <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:mo>∼</mml:mo> </mml:mrow> <mml:mn>40</mml:mn> <mml:mi mathvariant="normal">%</mml:mi> </mml:mrow> </mml:math> lower <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msubsup> <mml:mi>n</mml:mi> <mml:mrow> <mml:mi mathvariant="normal">e</mml:mi> <mml:mo>,</mml:mo> <mml:mi>sep</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>OMP</mml:mi> </mml:mrow> </mml:msubsup> </mml:mrow> </mml:math> in the closed divertor. These differences between divertor closure diminish when the midplane fueling is used. The analysis of all four scenarios (midplane/LD fueling in closed/open divertor) show that divertor closure and localized fueling work in synergy to create the optimized neutral trapping and energy dissipation, promoting detachment onset at lower <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msubsup> <mml:mi>n</mml:mi> <mml:mrow> <mml:mi mathvariant="normal">e</mml:mi> <mml:mo>,</mml:mo> <mml:mi>sep</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>OMP</mml:mi> </mml:mrow> </mml:msubsup> </mml:mrow> </mml:math> . This work demonstrates that divertor closure and localized fueling can facilitate detachment onset at lower <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msubsup> <mml:mi>n</mml:mi> <mml:mrow> <mml:mi mathvariant="normal">e</mml:mi> <mml:mo>,</mml:mo> <mml:mi>sep</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>OMP</mml:mi> </mml:mrow> </mml:msubsup> </mml:mrow> </mml:math> , highlighting the importance of an integrated approach to divertor optimization.