Theoretical explanations of I-mode impurity removal and H-mode poloidal pedestal asymmetries

Usage of high-z wall materials switches the fusion challenge from heat handling to impurity removal. I propose the first method of measuring the radial impurity flux from available diagnostics. H-mode was discovered 35 years ago to quadruple fusion power, and later explained by turbulence reduction by sheared flows. A decade ago, I-mode operation was discovered to have the same property, while removing impurities and providing free fueling. Thanks to the measuring method developed, I explain the outward radial impurity flux without invoking a sometimes undetected turbulent mode. This is supported by the observed E×B flow shear, whch also explains the desired energy confinement via turbulence reduction.

Stronger poloidal asymmetries than predicted by the most comprehensive neoclassical models have been measured, calling into question the reduction of turbulence in H-mode tokamak pedestals. I have developed the first self-consistent theoretical model retaining the impurity diamagnetic flow and the two-dimensional radial flow features. It successfully explains collisionally the experimental in-out asymmetries; thus making them consistent with H-mode pedestal turbulence reduction.