Neoclassical tearing modes are shown to be the MHD phenomenon that limits the achievable in long pulse discharges both in ASDEX Upgrade and in COMPASS-D. The experimental data are consistent with a generalized Rutherford equation including the effect of polarization currents induced by the motion of the island through the plasma. Possible strategies to avoid or reduce the effect of neoclassical tearing modes are discussed.
Influence of rotation on the (m, n) = (3, 2) neoclassical tearing mode threshold in the ASDEX Upgrade