A toroidal, nonlinear, electrostatic fluid-kinetic hybrid electron model is formulated for global gyrokinetic particle simulations of driftwave turbulence in fusion plasmas. Numerical properties are improved by an expansion of the electron response using a smallness parameter of the ratio of driftwave frequency to electron transit frequency. Linear simulations accurately recover the real frequency and growth rate of toroidal ion temperature gradient (ITG) instability. Trapped electrons increase the ITG growth rate by mostly not responding to the ITG modes. Nonlinear simulations of ITG turbulence find that the electron thermal and particle transport are much smaller than the ion thermal transport and that small scale zonal flows are generated through nonlinear interactions of the trapped electrons with the turbulence.

A new ⌬Ј shooting code has been developed to investigate tokamak plasma tearing mode stability in a cylinder and large aspect ratio (⑀р0.25) toroidal geometries, neglecting toroidal mode coupling. A different computational algorithm is used ͑shooting out from the singular surface instead of into it͒ to resolve the strong singularities at the mode rational surface, particularly in the presence of the finite pressure term. Numerical results compare favorably with Furth et al. ͓H. P. Furth et al., Phys. Fluids 16, 1054 ͑1973͔͒ results. The effects of finite pressure, which are shown to decrease ⌬Ј, are discussed. It is shown that the distortion of the flux surfaces by the Shafranov shift, which modifies the geometry metric elements, stabilizes the tearing mode significantly, even in a low-␤ regime before the toroidal magnetic curvature effects come into play.

A new phenomenon has been found during the nonlinear stage of the tokamak sawtooth crash in relatively high ␤ plasmas. The m/nϭ1/1 magnetic island evolution gives rise to convection of the pressure inside the qϭ1 radius and builds up steep pressure gradient across the island separatrix, and thereby trigger ballooning instabilities below the threshold at the equilibrium. Effects of the ballooning modes on the magnetic reconnection process during the sawtooth crash are discussed.

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Electromagnetic gyrokinetic simulation in toroidal geometry is developed based on a fluid-kinetic hybrid electron model. The Alfven wave propagation in a fully global gyrokinetic particle simulation is investigated. In the long-wavelength magnetohydrodynamic limit, shear Alfven wave oscillations, continuum damping, and the appearance of the frequency gap in toroidal geometries are demonstrated. Wave propagation across the magnetic field ͑kinetic Alfven wave͒ is examined by comparing the simulation results with the theoretical dispersion relation. Furthermore, finite-beta stabilization of the ion temperature gradient mode and the onset of the kinetic ballooning mode are demonstrated.