A two-term model of the confinement in Elmy H-modes using the global confinement and pedestal databases

Abstract

Two different physical models of the H-mode pedestal are tested against the joint pedestal–core database. The first is a confinement model in which the transport down the steep edge gradient is assumed to be dominated by thermal conduction. The second model is a magnetohydrodynamics (MHD) limit model in which it is assumed that the dominant loss mechanism is by the edge localized modes (ELMs), the pressure gradient being determined by a MHD stability limit. These models are then combined with models for the core and shown to give a good fit to the ELMy H-mode database. The resulting two-term scaling expressions are shown to give very similar predictions for the confinement time, in the next step machines ITER and FIRE, to that of the one-term model IPB98(y,2). The predicted stored energy in the pedestal is 28–50% of the total stored energy.