Mode-analytical Examination of Vortex Dynamics of a Pure Electron Plasma in the Relaxation to a Meta-equilibrium Distribution.

Vortex patches of intense density generated by the diocotron instability in a magnetized pure electron plasma merge each other accompanied by the production of filaments and finally relax to a bell shape distribution surrounded by a halo of low-density electrons. Here we reexamine the vortical dynamics in terms of the time evolution of the power spectrum in the mode-number space. Triggered by the instability, the initial axisymmetric ring distribution is deformed and torn into mesoscopic blobs, and a distribution of radial flux is generated around the blobs. In the merging process between vortex patches, the energy spectrum expands toward higher mode-number space, while the dominant mode shifts downward to lower mode numbers as this process proceeds. The turbulent period characterized by the repeated mergers is accompanied by a fast reduction of the enstrophy. During this relaxation the energy and the angular momentum of the whole plasma system remain conserved. In a slow process after the rapid relaxation a convex profile appears in the density distribution accompanied by the recovery of a symmetric distribution of the azimuthal flux. The spectra in the final state concentrate at symmetric modes with a slight contribution from orbiting motion of the plasma column. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]