Controlled Experiment of Relaxation Processes of Many-Particle System Using Strongly Magnetized Nonneutral Plasma

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Collective interactions among particles of strongly magnetized pure electron plasma appear as vortex motion. The phenomena that string-shaped high-density groups (clumps) of electrons form highly symmetric arrays have been coined "vortex crystal formation" and attracting much attention as a representative example of self-organization processes. In spite of high academic curiosity, the physical mechanism leading to the ordered states is far from full understanding. The purpose of this project is to physically explore each stage of the self-organization process on one hand and to build an instrumental and methodical basis for next generation of experimental studies by employing strong magnetic field on the other.Major steps toward physical understanding consist of three achievements : (1) Bifurcation between merger and closely-separated states of clumps is found to critically depend on the depth and width of the depletion belt self-generated in the background distribution between the clu … More mps. [Soga, Phys. Plasmas 2003] (2) The background populations curb the clumps' orbital motion, guide them to symmetric configurations and eventually keep them at the crystal lattice. [Sanpei, Phys. Rev. E (2003)] (3) Application of a rotating wave field to a distribution of magnetized electrons leads to a substantial compression of the density distribution when the dispersion of the wave satisfies the radical boundary conditions imposed by the conducting wall and the plasma density profile. However the matching condition includes self-adjustment of the density profile and resonance broadening, suggesting another type of self-organization of the plasma coupled with external fields. [Soga, JPFR-SR6 2004]A new plasma trap operatable with strong magnetic filed up to 2.2T is constructed together with the installation of a newly developed optical transfer system for observation of fine structures in the electron density distribution from a weal magnetic field zone.[Aoki, JJAP 2004] It has been successfully observed that finer structures are generated under the higher magnetic field. The Malmberg trap configuration, best suited to vortex experiments, has not shown confinement time longer than 200s. The Mohri trap configuration, suited to generate Penning type equilibria, has led to the confinement time exceeding500s. The long confinement time is the basis for the advanced study of relaxation toward equilibrium or transition between equilibrium states. This program has successfully prepared the starting point for the next generation of experimental studies of relaxation. Less