The dissipative self-orgmization of the plasma pressure and current in tokamaks is investigated through interactions between boorsuap cumnt and the anomalous transpoa due to self-sustained turbulence. The seongly reduced magnetic shea due to the press-driven current and the mametic m is shift cause B reduction in the anomalous mspott, which enhances the plasma pressure and bootstrap current and leads to a transition to a high-fi, plasma. The threshold is given by 0.2 1. Simulation results are compared with experimental obscmations.Plasma transport studies in toroidal devices have shown, for a wide range of parameters, that the energy confinement time SE, the ratio of the internal energy W, to the input power P,,, decreases with increase in the heating power. This phenomenon has been known as L-mode confinement [l]. Attention has been directed to improved confinement modes in tokamak plasmas [Z, 31. A spontaneous and rapid change in the transport fluxes was found in the transition from the L-mode to an improved mode known as the H-mode [Z]. One of the working hypotheses for the H-mode is a bifurcation in the radial electric field, E, [4]. The existence of a sudden change in E, [5] and rapid reduction in ion losses [6] has been confirmed experimentally. Although the electric-field bifurcation seems to explain the Hmode phenomena, different mechanisms could cause other improved modes. Understanding anomalous fm~~sport and the improved modes in tokamaks is a real challenge for modem plasma physics.Recently, high-p, plasmas have been studied experimentally [7, XI; pp is the ratio of

The effect of electron temperature perturbation induced by local heating on the tearing mode activity is investigated by simulations based on the reduced set of resistive MHD equations, with the transport equation of electron temperature. The effect of poloidal plasma rotation is also considered in the simulations. It is shown that the local heating can suppress the m = 2 tearing mode instability when the 0 point of the rotating magnetic island is effectively heated.While perpendicular thermal conduction imposes a lower limit on the degree of localization of the achievable heating, the ratio of parallel to perpendicular conduction is shown to determine the heating power necessary for complete stabilization of the tearing mode.

Simulations of dynamics of tearing modes based on a 4-field reduced magneto hydro dynamics model are performed, laying an emphasis on interaction with microscopic and transport processes. The simulation results show the importance of turbulent fluctuations for the onset of tearing mode. The helical current perturbation associated with a magnetic island is studied. The perturbed bootstrap current has a structure in the magnetic island (including a phase difference), indicating the need to improve assumptions in the theory of neoclassical tearing mode.

Novel features of the rapid growth and the nonlinear dynamics of driven magnetic islands in rotating plasmas are studied by nonlinear magnetohydrodynamics simulations. The transition phase of the magnetic island evolution is found between the rapid growth phase and the Rutherford-like phase in the low resistivity regime. It is shown that the rapid growth of the magnetic island is associated with its deformation that leads to the secondary magnetic island formation around the original X-points. The suppressed state is characterized by the asymmetric deformation of the magnetic island caused by the non-monotonic torque profile within the island separatrix. In the regime of the high magnetic flux input rate, the critical magnetic island width shows weak dependence on viscosity while it noticeably depends on resistivity. It is conjectured that this is a result of the effect of the Alfven type interaction between the rotating plasma and the fast growing external magnetic perturbation.

The effect of poloidally mode coupled, ballooning type electrostatic drift waves on a magnetic island has been studied both analytically and numerically. It has been shown quantitatively that particle orbits become stochastic and their behavior can be a possible candidate for the radial plasma transport across a magnetic island of a tokamak. The transport is significant in that it takes place even when the flux surface is not destroyed. The mechanism of the stochasticity generation is understood as an overlapping of secondary islands caused by resonance between periodic particle motions in the magnetic island and Fourier modes of E×B drift due to the electrostatic drift waves. The diffusion process perpendicular to magnetic surface has been analyzed by approximating the distribution to the Gaussian type. In addition, local diffusion process in the vicinity of Kolmogorov, Arnold, and Moser surfaces has been discussed.