High βN conditions have been sustained in JET discharges with an internal transport barrier (ITB) by controlling edge conditions and pressure peaking. The behaviour of ideal and resistive MHD instabilities at high βN has been studied as a function of pressure peaking. The duration of the high βN phase was limited by interaction with the septum of the Gas Box divertor. ITB triggering and evolution are in good agreement with the condition for turbulence suppression by E × B shear flow.
The role of zonal flows and predator–prey oscillations in triggering the formation of edge and core transport barriers