Dynamic behavior of structure trnsition phenomena in nonequilibrium and nonlinear plasmas in open systems

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Nonlinear MHD simulations on relaxation phenomena in spherical tokamak and helical plasmas, including 3D HINT equilibrium computations, are executed. The dynamics of global relaxation phenomena in spherical tokamak have been revealed. We analyze the sawtooth and the internal reconnection event (IRE). For the sawtooth case, a new nonlinear trigger mechanism is found, in which the n=1 activity in the core region is subsequently excited by development of higher n ballooning modes in the periphery region. After a process of pressure collapse, the torus returns to a state close to the axisymmetric initial configuration but with a broader pressure profile. The overall shape of the torus surface does not change throughout the event. On the other hand, simulations for IRE show a large distortion of the torus. The differences arise from only slight discrepancies in the initial profiles. The 3D equilibrium code HINT, which does not assume the existence of magnetic surfaces, is modified in a couple of directions to extend the functions. A new MHD simulation code for a full three dimensional geometry of helical plasmas were developed. A relaxation phenomenon driven by pressure driven instabilities in the LHD configuration was observed, which was not destructive but caused transition to a new equilibrium. An initial phase of plasma deformations is dominated by medium-n resistive ballooning instability. In the later stage, a well-confined state is recovered by having spontaneous evolution to a broader pressure profile. Virtual reality display system was developed as an advanced visualization method to understand complex phenomena.