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Abstract:
The development of a predictive capability for the characteristics of the H-mode pedestal and ELMs is important in predicting tokamak reactor performance. The H-mode pedestal effects core confinement through temperature profile stiffness. The ELM power flux can significantly impact divertor design. We discuss progress in these areas through inter-machine comparison under the venue of the International Tokamak Physics Activity, ITPA. The pressure in the H-mode transport barrier region is typically set by the ELM cycle rather than transport. Several features of the ELM onset conditions are consistent with an ideal peeling-ballooning mode instability: 1) strong shape dependence, 2) mode structure, 3) reduced p' at high collisionality, 4) p' dependence on transport barrier width. Type I ELM energy loss is found to be proportional to the energy in the H-mode pedestal. There is some consistency between the peeling-ballooning mode radial width and the ELM size. Type I ELM energy loss is reduced at high density to levels that would be tolerable in a reactor scale device through reduced conductive loss and possibly shift to a more radially localized instability.
