Measurement of poloidal flow, radial electric field and E x B shearing rates at ASDEX Upgrade

The theoretical model of transport reduction by E x B shear decorrelation i s tested experimentally for ASDEX Upgrade discharges. The radial force bala nce is used to determine the radial electric field from charge exchange rec ombination spectroscopy measurements. As the effective rate coefficient for photon emission of the charge exchange process depends on the collision en ergy, the alignment of the lines of sight with respect to the neutral beam gives rise to apparent velocities and temperatures. In addition, the gyro-m otion of the observed species along with the finite lifetime of the observe d excited state leads to lineshifts in spectra measured in the poloidal dir ection. Both effects require corrections, which will be discussed. The corr ections are tested using the measurements of a discharge with a locked mode . From the profiles of an H mode discharge with improved confinement and a discharge with an internal transport barrier (ITB) the ion heat transport c oefficients, E x B shearing rates and the maximum linear growth rates of th e instabilities are calculated. Comparison of these results supports the as sumption that turbulent transport due to the ion temperature gradient insta bility is suppressed inside the transport barrier in the ITB discharge. How ever, due to the dominant influence of the toroidal rotation velocity on th e central E x B shear, they do not prove the shear decorrelation model, bec ause E-r naturally rises during the phases with improved confinement if unb alanced neutral beam heating is applied.