Understanding of H mode pedestal characteristics using the multimachine pedestal database

With use of a multimachine pedestal database, essential issues for each regime of ELM types areinvestigated. They include (i) understanding and prediction of pedestal pressure during type I ELMs,a reference operation mode of a future tokamak reactor; (ii) identification of the operation regime oftype II ELMs, which have small ELM amplitude with good confinement characteristics; (iii) identificationof the upper stability boundary of type III ELMs for access to the higher confinement regimes withtype I or II ELMs; (iv) understanding the relation between core confinement and pedestal temperaturein conjunction with the confinement degradation in high density discharges. Both scaling and modelbased approaches for expressing pedestal pressure are shown to roughly scale the experimental datawell and could be used to make initial predictions for a future reactor. q and δ are identifiedas important parameters for obtaining the type II ELM regime. A theoretical model of type III ELMs isshown to reproduce the upper stability boundary reasonably well. It is shown that there exists somecritical pedestal temperature below which the core confinement starts to degrade. It is also shown thatit is possible to obtain improved pedestal conditions for good confinement in high density dischargesby increasing the plasma triangularity.