Transport barriers in electron acid ion transport dominated regimes

Confinement improvement beyond the usual L-mode proceeds in most cases thro ugh the formation of localized transport barriers in the edge (H-mode) or i n the interior regions of the plasma (ITBs). The standard interpretation of this is the quenching of the usually prevailing turbulence by the formatio n of layers of sheared E x B rotation. Regarding interior transport barrier s, this phenomenon has been observed in two distinctively different situati ons, with predominant ion or electron heating, and T-e either significantly smaller or larger than T-i. The reactor relevant regime is, however, one w ith approximately equal T-e and T-i. The availability of ECRH (and, to a le sser degree, also that of LH or FW heating) has allowed the study of the ef fect of the T-e/T-i ratio in a controlled way. The standard transport model of ion-temperature-gradient and trapped-electron-mode-driven turbulence pr edicts (for situations with significant ion heating) a negative effect of a n increase in this ratio. Experimental results show, however, that this con finement deterioration can be avoided in certain situations. These observat ions can be reconciled with theoretical expectations, if the simultaneous i ncrease in Shafranov shift, which can reverse the theoretical predictions, is taken into account.