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

Divertor detachment with the 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 ELMs operation, characterized by the reduced pedestal ion temperature gradient ∇T_i and the enhanced electron density gradient ∇n_e. The presence of minority nitrogen at the edge plasma, which results from the divertor nitrogen seeding, contributes to the rise of ion temperature T_i in the confinement region by suppressing the turbulence through the impurity dilution effect and E×B shear. The increased ion temperature T_i and electron density n_e compensate the energy loss resulted 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 on the fundamental physics governing the closed divertor detachment with sustainable high-performance plasmas through divertor nitrogen seeding.