Wavelet analysis of turbulent structures in a magnetized pure electron plasma

Abstract

Wavelet analysis is applied to examine two-dimensional (2D) structures of pure electron plasma density distribution observed in a free-decaying turbulent stage starting from an unstable distribution. In contrast to the traditional Fourier analysis, the simultaneous resolution of the structures in terms of the physical coordinates and length scales (or wave numbers) allows us to discriminate instrumental dot noises without generating spurious high wave-number components that tend to distort the energy and enstrophy spectra. With this analysis at each time segment, the following features are clearly observed: Intermittency in the structures of electron density distribution, that is equivalent to the 2D vorticity distribution, is clearly demonstrated in terms of the scale-resolved kurtosis. The upward cascade of the enstrophy in the wave-number space is associated with the development of vortex filamentation in the physical space. Controlled discrimination of the coherent component in terms of the wavelet coefficients of the observed density distribution indicates significant contribution of persisting coherent vortices in steepening the energy spectra of the 2D turbulence far above the theoretically predicted power law of k(-3).