The electron temperature gradient (ETG) driven drift mode is studied using an advanced fluid model retaining effects of nonadiabatic ions, Debye shielding and the electron diamagnetic heat flow. The derived eigenmode equation is solved analytically in the strong ballooning limit. Both the toroidal and the slab branch of the ETG mode are included and the fluid growth rates are compared with gyrokinetic results. The role of nonadiabatic ion response is found to have a stabilizing effect on ETG-mode in the lower-hybrid regime. Strong stabilization is also found due to Debye shielding effect for λDe2/ρe2>1. In particular, it is shown that nonadiabatic ion response can result in inward flows of particles for peaked density profiles.

Dissipation range spectra for incompressible magnetohydrodynamic turbulence are derived for isotropic viscosity μ and resistivity η. The spectra are obtained from heuristic closures of spectral transfer correlations for cases with Pm=μ/η≤1, where Pm is the magnetic Prandtl number. Familiar inertial range power laws are modified by exponential factors that dominate spectral falloff in the dissipation range. Spectral forms are sensitive to alignment between flow and magnetic field. There are as many as four Kolmogorov wavenumbers that parametrize the transition between inertial and dissipative behavior and enter corresponding spectral forms. They depend on the values of the viscosity and resistivity and on the nature of alignment in inertial and dissipation ranges.

A simple large-aspect-ratio (R 0 =r) circular equilibrium model is developed for low-beta reversed field pinch (RFP) geometry. The model is suitable for treating small scale instability and turbulent transport driven by ion temperature gradient (ITG) and related electron drift modes in gyrokinetic simulations. The equilibrium model is an RFP generalization of the common tokamak s-a model to small safety factor (q), where the poloidal field dominates the toroidal field. The model accommodates the RFP toroidal field reversal (where q vanishes) by generalizing the cylindrical force-free Bessel function model (BFM) [J. B. Taylor, Phys. Rev. Lett. 33, 1139 (1974)] to toroidal geometry. The global equilibrium can be described in terms of the RFP field reversal and pinch parameters ½F; H. This new toroidal Bessel function model (TBFM) has been incorporated into the gyrokinetic code GYRO [J. Candy and R. E. Waltz, J.Comput. Phys. 186, 545 (2003)] and used here to explore local electrostatic ITG adiabatic electron instability rates for typical low-q RFP parameters. V

A simple generic one-dimensional continuum model of driven dissipative systems is proposed to explain self-organized bursty heat transport in tokamaks. Extensive numerical simulations of this model reproduce many features of present day tokamaks such as submarginal temperature profiles, intermittent transport events, 1/f scaling of the frequency spectra, propagating fronts, etc. This model utilizes a minimal set of phenomenological parameters, which may be determined from experiments and/or simulations. Analytical and physical understanding of the observed features has also been attempted.

Analytical investigations of several linear and nonlinear features of drift resistive ballooning mode (DRBM) have been carried out. The physics of this mode has been elucidated, as well as the parameter space where it is important. Based on the linear theory, it is shown that the growth of the high-m DRBM is crucially dependent on the poloidal mode number and finite Larmor radius effects i.e., drift parameter). The modulational instability of the zonal flow in a background of DRBM turbulence (using the parametric instability methods) has also been presented. Furthermore, an estimate of the particle transport due to DRBM (with its amplitude level limited by zonal flows) has also been computed. Finally, comparison with the transport estimated from the mixing length arguments and earlier simulations by Rogers and Drake [B. N. Rogers and J. F. Drake, Phys. Rev. Lett. 81, 4396 (1998)] are also presented.