The characteristics of the internal transport barrier under reactor relevant conditions in JT-60U weak shear plasmas

Abstract

The characteristics of the internal transport barrier (ITB) have been investigated under reactor relevant conditions with edge fuelling and electron heating in JT-60U weak shear plasmas. In order to investigate the effects of edge fuelling and electron heating separately, two independent classes of experiments were performed, i.e. one with edge fuelling and ion dominant heating and the other with central beam fuelling and additional electron heating. High confinement was sustained at high density with edge fuelling by shallow pellet injection or supersonic molecular beam injection. The ion temperature (Ti) in the central region inside the ITB decreased due to cold pulse propagation even with edge fuelling. By optimizing the injection frequency and the penetration depth, the decreased central Ti recovered and a good ITB was sustained with enhanced pedestal pressure. The Ti-ITB also degraded significantly with electron cyclotron heating (ECH), when the stiffness feature was strong in the electron temperature (Te) profile. The ion thermal diffusivity in the ITB region increased with the electron thermal diffusivity, indicating the existence of a clear relation between ion and electron thermal transport. On the other hand, the Ti-ITB remained unchanged or even grew, when the stiffness feature was weak in the Te profile. The density fluctuation level at the ITB seemed unchanged during ECH; however, the correlation length became longer in the Ti-ITB degradation case and shorter in the Ti-ITB unchanging case.