Influence of neoclassical tearing modes on energy confinement

The degradation in confinement due to neoclassical tearing modes has been i nvestigated for the (3, 2) mode at ASDEX Upgrade. Besides the increased hea t transport across the magnetic island, a decreased plasma density after th e onset of the mode leads to a further deterioration in confinement. The re lative energy loss compared to the prediction of standard scaling law satur ates for large pressures at around 25%. The experimental results have been compared with numerical simulations of the nonlinear growth of neoclassical islands accounting for the increased heat transport induced by the magneti c islands. Except for the effect of the density decrease, good agreement be tween the observations and the simulation results is found.