Radiation enhancement and impurity behavior in JT-60U reversed shear discharges

Abstract In order to extend the high-confinement reversed shear regime with an internal transport barrier (ITB) toward high radiation loss power, Ne and Ar injection have been investigated in JT-60U. With Ne injection, high confinement ( H 89PL >2.4, HH 98(y,2) >1.6) and high radiation loss power fraction (>80%) were simultaneously obtained at high density (>0.7 n GW ). The radiation loss power was enhanced both in the main plasma and in the divertor plasma. With divertor plasma detachment and an X-point MARFE, the ITB was pronounced and the H 89PL factor reached 1.8. However, Ar injection resulted in excessive radiation loss enhancement inside the ITB. The Ne and the C density profile were similar to the electron density profile, and their accumulation was not significant. On the other hand, Ar showed accumulation inside the ITB.