Understanding of H mode pedestal characteristics using the multimachine pedestal database

With use of a multimachine pedestal database, essential issues for each reg ime of ELM types are investigated. They include (i) understanding and predi ction of pedestal pressure during type I ELMs, a reference operation mode o f a future tokamak reactor; (ii) identification of the operation regime of type II ELMs, which have small ELM amplitude with good confinement characte ristics; (iii) identification of the upper stability boundary of type III E LMs for access to the higher confinement regimes with type I or II ELMs; (i v) understanding the relation between core confinement and pedestal tempera ture in conjunction with the confinement degradation in high density discha rges. Both scaling and model based approaches for expressing pedestal press ure are shown to roughly scale the experimental data well and could be used to make initial predictions for a future reactor. q and delta are identifi ed as important parameters for obtaining the type II ELM regime. A theoreti cal model of type III ELMs is shown to reproduce the upper stability bounda ry reasonably well. It is shown that there exists some critical pedestal te mperature below which the core confinement starts to degrade. It is also sh own that it is possible to obtain improved pedestal conditions for good con finement in high density discharges by increasing the plasma triangularity.