Loss of confinement due to reduction of the edge pedestal in JET

Abstract

There are various conditions in JET under which the energy confinement of a plasma is reduced from H mode towards L mode levels. Examples are reported here for which the loss of confinement is associated with a reduction of the electron pressure pedestal. This loss is brought about by strong gas puffing that increases the frequency of edge localized modes (ELMs). The effect of ELMs on confinement is modelled, and used to explain the observed degradation of confinement. The model is generalized for application to other machines.