Study of MHD Oscillations in TEXT Using Magnetic and Soft X Ray Diagnostics

摘要

MHD fluctuations in TEXT were observed with poloidal and toroidal arrays of external Mirnov coils. Correlation and Fourier analyses in the spatial domain were performed to obtain time dependent mode spectra. Nonlinear mode coupling during disruptions was studied with bispectral analysis techniques. A decreasing mode hierarchy was observed during the current rise with q/sub lim//m approx. = 1.2. An inverse relationship between the amplitude and frequency of Mirnov oscillations was found. Disruptions were accompanied by a significant decrease in frequency. Both m/n = 3/2 and 2/1 modes were observed before a disruption, however, identification of modes was not possible during the time interval between the precursor and the disruption. The apparent poloidal rotation of the plasma was in the electron diamagnetic drift direction and the opposite rotation appears to be highly unstable. Phase locking of the internal m = 1 mode and external m = 2 mode was also observed. Soft x ray fluctuations were studied to reveal the evolution of internal MHD activity. (ERA citation 09:017762)