Application of wavelet spectral analysis to plasma fluctuation measurements using beam emission spectroscopy

Beam emission spectroscopy (BES) measures localized density fluctuations in fusion plasma turbulence. A wavelet transform method of spectral analysis is applied to BES data to extract fluctuations without the long time-averag ing characteristic of Fourier transform spectral analysis methods. This tec hnique is used to observe an abrupt (similar to 100 mu s) L-H transition on DIII-D. Wavelet-based cross correlation analysis can be used to obtain flu ctuations of poloidal rotation velocity, and suggests opportunity for measu rement of electrostatic potential fluctuation measurements. (C) 1999 Americ an Institute of Physics. [S0034-6748(99)64901-2].