Application of a bandpower correlation method to the statistical analysis of MHD bursts in quiescent Wendelstein-7 AS stellarator plasmas (original) (raw)
2007, Plasma Physics and Controlled Fusion
This paper presents the analysis of Mirnov coil data from pure electron-cyclotron resonance heated Wendelstein-7 AS discharges with transient magnetohydrodynamical (MHD) mode activity in otherwise MHD inactive plasmas. Amplitude modulations were found on the 100 µs time scale, expected to originate from transient changes of the plasma pressure profile by anomalous transport events. The analysis was done using our custom developed bandpower correlation method, which combines short-time Fourier transform for the decomposition of the signal with a correlation analysis to quantitatively characterize the statistical connection between the modulation in the power of different MHD modes. The effect of a confinement transition (near a rational rotational transform) on the correlation between the power modulation of different frequency modes has been studied. As high as 50% correlation has been found between different frequencies in 'bad confinement' shots with enhanced transient transport, while for 'good confinement' shots no significant correlation was observed.
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