Theoretical explanation of I-mode impurity removal and energy confinement

Improved (I) mode operation maintains the beneficial high energy confinement of high (H) mode while also providing natural fueling to compensate for impurity removal. We show outward collisional radial impurity flux is the robust distinguishing characteristic between I-mode and H-mode, rather than the turbulent weakly coherent mode that is sometimes undetected, perhaps due to its strong spatial localization. In both regimes the E x B flow shear observed may break up eddies to reduce the turbulence level, leading to good bulk energy confinement.