Elementary Processes of Free-decaying Two-dimensional Turbulence in Magnetized Pure Electron Plasmas

Elementary processes of two-dimensional (2D) turbulence have been examined by extensive analyses of finescale structures in the density distribution of a magnetized pure electron plasma that evolves from an unstable initial state to a single-peaked stable distribution through successive mergers of vortex patches. Fourier-based analyses have revealed that the spectral dynamics in the wave-number k space is qualitatively consistent with the theoretical picture of 2D turbulence, i.e., while the energy is transferred downward, the enstrophy cascades upward in the wave-number region larger than kin j corresponding to the size of vortex patches, and the energy spectrum E(k) shows a power-law scaling k−α with α > 3. By applying wavelet analyses to the observed density distributions, this spectral dynamics is connected directly to the vortex dynamics in the physical space. With the simultaneous resolution in the physical coordinates and wave numbers, we have observed that the enstrophy cascade is associated with the filamentation process of vortex structures. Moreover, controlled discrimination of the coherent component in terms of the wavelet coefficients indicates significant contribution of coherent vortices in steepening the energy spectrum far above the theoretical prediction of k−3.