Control of divertor heat load by Ar injection with keeping high performance in ELMy H-mode plasmas on JT-60U

In ELMy H-mode plasmas of Japan Atomic Energy Research Institute Tokamak-60 Upgrade, extension of a high confinement regime toward high density and high radiation-loss-power fraction has been investigated by Ar injection. With injecting Ar and putting the outer strike point on the top of divertor dome, confinement improvement, electron density, and radiation-loss-power fraction reached the ITER relevant regime; the thermal energy confinement time was as high as that the International Tokamak Experimental Reactor ELMy H-mode scaling IPB98(y,2), the electron density is ∼80% of the Greenwald density, and the radiation-loss-power fraction is ∼0.8. Although electron density profile is slightly peaked with Ar injection, the confinement improvement is mainly attributed to the improvement of ion transport. Moreover, the maximum divertor heat load due to ELMs has been reduced by a factor of 3–5 with keeping high confinement. ELM activity can be controlled by injecting Ar and changing the strike point position.