The edge operational space in JET

In this paper we investigate differences of the ELM behaviour between RF and NE heated PI-mode discharges in JET. The main result of this investigation is that the edge pedestal pressure with NE heating is higher than with RF heating for equal power fluxes crossing the separatrix. This can be explained by a higher population of fast ions in the edge region in the case of NB heating. Using data from NE heated steady-state PI-modes we derive a scaling law for the width of the transport barrier. We find that the barrier width is proportional to the poloidal Larmor radius, which in turn is controlled by the ion population with the highest energy in the plasma edge. (C) 1999 JET Joint Undertaking, published by Elsevier Science B.V. All rights reserved.