Facilitated core-edge integration through divertor nitrogen seeding in the HL-2A tokamak

Abstract

A divertor detachment with sustainable high-performance plasmas has been achieved through divertor nitrogen seeding in the HL-2A tokamak. The closed divertor structure facilitates achieving high divertor neutral pressure due to its efficient particle containment effect as demonstrated by both experimental and SOLPS simulation results, which aids in achieving the divertor detachment. The radiative divertor is conducive to high-frequency small edge localized modes (ELMs) operation, characterized by a reduced pedestal ion temperature gradient $\nabla {T_{\text{i}}}$ and the enhanced electron density gradient $\nabla {n_{\text{e}}}$ . The presence of minority nitrogen at the edge plasma, which results from the divertor nitrogen seeding, contributes to the increase of ion temperature ${T_{\text{i}}}$ in the confinement region by suppressing the turbulence through the impurity dilution effect and ${\mathbf{E}} \times {\mathbf{B}}$ shear. The increased ion temperature ${T_{\text{i}}}$ and electron density $n_e$ compensate the energy loss resulting from the increased edge radiation during detachment, which contributes to the confinement sustainment combined with reduced pedestal energy loss caused by small ELMs. This work advances our understanding of the fundamental physics governing closed divertor detachment with sustainable high-performance plasmas through divertor nitrogen seeding.

Keywords

• core-edge integration
• detachment
• small edge localized mode
• closed divertor
• nitrogen seeding
• HL-2A