Wavelet and Fourier analysis of zonal flows and density fluctuations in JIPP T-llU tokamak plasmas

Abstract

Wavelet and two-dimensional Fourier analyses of local potential and density signals were conducted. These signals were obtained in the core region of tokamak plasmas by a multiple-sample-volume heavy ion beam probe. In the low-density Ohmic plasma where the electron temperature is much higher than that of the ions, the high-frequency (HF) zonal flow in geodesic acoustic mode frequency region is more energetic than the low-frequency zonal flow from 10 to 1000 Hz in terms of integrated intensity. This result is in sharp contrast to the results of ITG simulations of the tokamak plasmas. The HF zonal flow has a short lifetime (a few cycles). The wavelet spectra of density are much more chaotic than those of potential turbulence, changing the amplitude and frequency of the dominant modes more rapidly within the lifetime of the HF zonal flows. It was also found that HF parts of the density fluctuations are highly modulated by the HF zonal flows.