Scrape-off layer intermittency in the Castor tokamak

Abstract

Spatial–temporal intermittency of floating potential and ion saturation current fluctuations is analyzed by using data obtained from two probes arrays in the scrape-off layer of the CASTOR tokamak [Proceedings of the 1996 International Conference on Plasma Physics (Nagoya) (International Atomic Energy Agency, Vienna, 1997), Vol. I, p. 322]. For these ion saturation current fluctuations with non-Gaussian probability density functions, a conditional averaging analysis shows coherent structures with correlation lengths and lifetimes larger for larger amplitude conditions. Nevertheless, there is no evidence of such large structures in the potential fluctuations. Furthermore, wavelet transforms are used to analyze these nonstationary fluctuations and obtain details not observed with the Fourier technique. So, examining wavelet power and coherence spectra, strong intermittency is found for both kinds of fluctuations, in a time scale two orders of magnitude higher than that observed in the conditional analysis. Moreover, during the discharges the observed wavelet quadratic coupling alters intermittently for some low-frequency components.