MHD instabilities in TEXT discharges with high magnetic perturbation levels and ergodic magnetic limiter effects

Summary Form only given, as follows. Nondisrupting, high-MHD (large-amplitude B/sub Theta /) discharges have been investigated on TEXT. The MHD instability has been studied over a wide range of q/sub a/ for this type of discharge. Three diagnostic systems were used to explore the internal model structure of the perturbation: two soft X-ray arrays to provide tomographic data, a 36-channel FIR interferometer, and a heavy ion beam probe. The results indicate a different mode pattern from that associated with low-amplitude-B/sub Theta /, sawtoothing plasmas. During the discharges, the ergodic magnetic limiter is pulsed to perturb the magnetic configuration of the edge. Both an amplitude and frequency change of B/sub Theta / are observed during this pulse. These changes have been examined at different values of q/sub a/. With the aid of a nonlinear toroidal MHD code, a comparison has been made between modeled results and experimental data.<>