Improvement of angular momentum confinement with density peaking on ASDEX

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Abstract
Toroidal rotation velocity profiles during neutral beam injection on ASDEX have been investigated by means of charge exchange recombination spectroscopy. For both co- and counter-injection of neutral beams the ratio of the injected power and the line averaged electron density is found to be an essential experimental, parameter for the central rotation speed. With counter-injection, a continuous rise of rotation velocity and density is observed, indicating strong improvement of angular momentum confinement. This improvement is found to be strongly correlated with the peakedness of the density profile. Simple model calculations of momentum transport indicate that the increase of momentum confinement with density peaking can be partly attributed to the variation of torque deposition with the shape of the density profile.