LAUSR

Improved (I) mode operation maintains the beneficial improved energy confinement of high (H) mode operation while also providing natural fueling to compensate for impurity removal. We show that outward collisional radial impurity flux occurs for I-mode, making the presence of turbulence compatible but unnecessary to explain I-mode impurity removal. We propose that the neoclassical radial impurity flux direction is a robust characteristic distinction 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 observed E × B flow shear can break up eddies to reduce the turbulence level, leading to good bulk energy confinement.