Role of Te/Ti and delνtor in ion heat transport of ASDEX Upgrade H-mode plasmas

Experiments in H-mode plasmas have shown that both heat and particle transport are sensitive to the ratio between electron and ion temperature (T-e/T-i). While decreasing T-e/T-i is beneficial for confinement, an increased electron heating in these so called 'hot ion plasmas' deteriorates the confinement. H-mode plasmas with low T-e/T-i are often accompanied by high toroidal rotation velocity (nu(phi)). Its gradient (del nu(phi)) can destabilize the ion temperature gradient mode (ITG) through its parallel component in the parallel velocity shear, but it has also stabilizing effects since it produces an E x B shearing rate (omega(ExB)). In this paper, the effects of electron heating on the ion heat transport is investigated in H-mode plasmas heated by neutral beam injection (NBI) and electron cyclotron heating (ECH). In particular, the correlation on T-e/T-i and del nu(phi) is studied and compared with calculations made with GLF23 and GS2. Experimentally it is shown that the normalized gradient length of the ions (R/L-Ti) is correlated with both T-e/T-i and del nu(phi): peaked ion temperature profiles are only obtained with low T-e/T-i and high del(nu phi), and vice-versa. When ECH is added, both ion heat and momentum transport are enhanced, leading to a drop of both the T-i and nu(phi) profiles. The effective growth rate gamma eff = gamma - omega(ExB) is calculated, with the mode growth rate gamma determined with GS2 and omega(ExB) with GLF23. The ion transport is enhanced due to the decrease of the ITG R/L-Ti threshold with increasing T-e/T-i. Comparison of the dependence of R/L-Ti on Te/Ti and del nu(phi) between experiments and modelling indicates that the deterioration of confinement cannot be explained by the changes in only T-e/T-i or del nu phi, but by the combined effects of both parameters. The changes in T-e/T-i act directly on the ITG threshold, while the ones in del(nu phi) modify the omega(ExB) shearing rate leading to changes in the effective threshold.