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.

The first linear global electromagnetic gyrokinetic particle simulation on the excitation of toroidicity induced Alfven eigenmode (TAE) by energetic particles is reported.With an increase in the energetic particle pressure, the TAE frequency moves down into the lower continuum. PACS numbers: 52.55.Fa, 52.35.Bj, 52.65.Tt Toroidicity induced Alfven eigenmode (TAE) 1-3 can play important roles in burning plasmas. The TAE modes can be excited when energetic particles, for example fusion born alpha particles, resonate with the phase velocity of the shear Alfven wave which resides within the frequency gap of the Alfven continuum.Shear Alfven wave oscillations, continuum damping, and the appearance of the frequency gap in toroidal geometries by gyrokinetic particle simulation have been recently reported. 4The simulation of Ref.4 is demonstrated in the long wavelength magnetohydrodynamic (MHD) like limit in the absence of kinetic ions. In this letter, taking exactly the same parameters 3,4 but adding the energetic ion particles, the first linear particle simulation on the excitation of the TAE modes is reported. The simulation is done without employing

Significant progress has been made on ASDEX Upgrade during the last two years in the basic understanding of transport, in the extension of the improved H-mode in parameter space and towards an integrated operating scenario and in the development of control methods for major performance limiting instabilities. The important features were the understanding of particle transport and the control of impurity accumulation based on it, the satisfactory operation with predominantly tungsten-clad walls, the improved H-mode operation over density ranges and for temperature ratios covering (non-simultaneously) the ITER requirements on ν*, n/nGW and Te/Ti, the ELM frequency control by pellet injection and the optimization of NTM suppression by DC-ECCD through variation of the launching angle. From these experiments an integrated scenario has emerged which extrapolates to a 50% improvement in n T τ or a 30% reduction of the required current when compared with the ITER base-line assumptions, with moderately peaked electron and controllable high-Z density profiles.

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.