The divertor detachment is important for the improved confinement mode (I-mode) to serve as a reliable operating scenario in future fusion reactors. A reproducible steady-state I-mode operation with the energy detachment of the inner target has been achieved with the lower single-null configuration on the Experimental Advanced Superconducting Tokamak (EAST). Compared to the high confinement mode (H-mode), I-mode has a lower electron temperature on the inner divertor target and can achieve energy detachment at a lower density. In addition, dedicated experiments on neon (Ne) seeding to assist the exhaust of steady-state heat flux in I-mode discharges have also been successfully carried out on EAST. A significant reduction of the particle flux caused by the Ne impurity radiation was observed at both inner and outer divertor targets without I-L back-transition on EAST for the first time. This may be due to the ‘corner effect’ of the EAST right-angled divertor with a high divertor closure, which can effectively trap the impurity particles and thus reduce the influence of impurity on the main plasma. Furthermore, good core-edge compatibility was also obtained in the detached I-mode plasma with a radiative divertor. This study offers an attractive scenario of I-mode operation for avoiding excessively high transient and steady-state heat loads simultaneously in future fusion reactors.
This paper reports the achievement of a steady-state I-mode operation with energy detachment on the EAST tokamak, which is important for future fusion reactors. I-mode has lower electron temperature and can achieve detachment at lower density compared to H-mode. Neon seeding experiments successfully reduced particle flux without I-L back-transition, likely due to the 'corner effect' of EAST's divertor design. This study offers an attractive scenario for avoiding high heat loads in future fusion reactors.