A set of dedicated JET experiments is described where the plasma elongation (k) and triangularity (δ) were varied separately in order to study the influence of plasma magnetic topology on the internal transport barrier (ITB). With low δ, type III ELMs were observed and ITBs readily generated. At the highest δ, large type I ELMs and ELM free phases were observed but, at best, only marginal ITBs. At fixed δ the increase of the elongation of internal magnetic surface have a beneficial effect on the transport quality of the ITB.
Characteristics and scaling of energy and particle losses during Type I ELMs in JET H-modes