TIME-SERIES ANALYSIS OF NONSTATIONARY PLASMA FLUCTUATIONS USING WAVELET TRANSFORMS

A wavelet or time-scale approach to analyzing a single time series and two time series, in which the fluctuating quantities are statisticall y nonstationary, is presented. The time scale and scale ''power spectr a'' are introduced and utilized to analyze transient potential fluctua tions measured at the core of sawtoothing TEXT-U plasmas. The results show features that have not been previously observed using any Fourier techniques. In addition, the linear time-scale ''coherence spectrum'' is developed to quantify the degree of Linear relationship between tw o nonstationary fluctuating quantities in the time-scale domain. Such a spectrum is also useful in tracking the time-varying phase differenc e. A numerical example is provided to demonstrate the efficacy of the time-scale spectra. (C) 1997 American Institute of Physics.