Studies on MHD oscillations on the TEXT tokamak

Low-frequency MHD oscillations in the TEXT tokamak are studied using an array of 40 soft-x-ray detectors and three arrays of magnetic pick-up coils including TEXT standard diagnostics. First, double-sawtooth oscillations observed during low q/sub lim/ discharges are presented. A partial reconnection of magnetic fields under a hollow current profile appears to be responsible for the oscillations. A condition for a partial reconnection in terms of the ratio of the two q = 1 radii is obtained with a simple analytical model based on Kadomtsev's argument, and compared with the experimental results. Second, experimental evidence of the correlation between sawtooth period and energy confinement time is presented. Inconsistency between the scaling of sawtooth period by Jahns et al. and the reconnection time of magnetic field lines due to m = 1 mode by Kadomtsev is discussed. Finally, the geometric characteristics of magnetic-field fluctuations is presented. Correlations dimensions are estimated for Mirnov oscillations and magnetic turbulence. In a stationary state, the attractor for the Mirnov oscillations is basically circular