Propagation of magnetic islands in the Er=0 frame of co-injected neutral beam driven discharges in the DIII-D tokamak

Measurements are made of the propagation frequency ω of tearing mode magnetic islands in the local Er=0 frame in co-injected neutral beam heated H-mode discharges in the DIII-D tokamak [J. L. Luxon et al., Plasma Physics and Controlled Fusion Research (International Atomic Energy Agency, Vienna, 1987), Vol. 1, p. 159]. Propagation is found to be in the ion diamagnetic drift direction with a frequency more than that of the diamagnetic drift frequency ωi* for modes near the axis and less than ωi* off-axis. This is consistent with the predicted stabilizing polarization current threshold for neoclassical tearing modes for all modes observed only if the condition 0<ω<ωi* is modified by |ωe*| or ηi effects, for example.