Core and edge confinement studies with different heating methods in JET

Abstract

A detailed comparison of core and edge confinement with different heating methods - NBI and ICRH - has been carried out in the ELMy H mode regime in JET with the Gas Box divertor. Transport in the core and characteristics of the edge pedestal have been assessed in discharges at 2.0 MA/2.6-2.7 T at a total input power level of 11-12 MW. The thermal core confinement has been found to be higher by about 10% in ICRH dominated discharges. Although this difference is well within the uncertainties of the thermal confinement estimation, it has been consistently found in similar experiments in the past and it may be related to the more peaked power deposition provided by ICRH. Local transport analysis carried out with the TRANSP code indicates that, independently of the NBI versus ICRH mix, ion conduction losses are the dominant energy loss channel. In contrast to previous experiments, the gas flow and density of NBI and ICRH discharges have been closely matched. In these conditions it has been found that both types of heating yield similar values of edge density and temperature and produce similar ELMs. The fact that the edge fast ion concentration can be varied from roughly 0.4% up to 4% without producing significant changes in the edge pedestal parameters is an indication that fast ions do not always play a dominant role in the edge stabilization between ELMs, especially in discharges with strong gas fuelling.