No abstract

Turbulence and transport due to fully toroidal ion temperature gradient driven drift waves and a collisionless trapped electron mode have been studied by mode coupling simulations and with the quasi-linear theory. Diffusion coefficients in good agreement with the simulations have been obtained. The observed tendency for equilibration of the temperature and density scale lengths leads to particle or heat pinch effects that are in agreement with experimental trends.

A simple quadratic dispersion relation is derived for electrostatic ion temperature gradient driven modes without expansion in the inverse aspect ratio. It is also shown that these modes experience the local curvature only on the outside of the magnetic surface.

It is shown that the toroidal ion temperature gradient (ITG) mode has an upper η i (higher η i ) stability regime for experimentally relevant parameter values in addition to the lower regime with the stability threshold (η ilow ) at η i around one (η i = L n /L T i where L n and L T i are the characteristic lengths for the density and ion temperature gradients). The ITG mode is studied with a focus on the upper η i stability regime and the β dependence (β = plasma pressure/magnetic pressure). The results of a gyrokinetic and a two-fluid model as well as a semilocal approximation are compared. It is shown that the upper stability threshold (η iup ) is very sensitive to and considerably reduced by finite-β effects. It is also sensitive to finite Larmor radius (FLR) effects and to ε n = 2L n /L B (L B is the characteristic length for the toroidal magnetic field gradient). Predictions and comparisons are made with data from a joint European torus (JET) optimized shear discharge and a JET hot ion H-mode (high-performance mode) discharge.

The ion temperature gradient driven ballooning mode is investigated using two-fluid, gyrofluid, and gyrokinetic descriptions. The linear eigenmode equation is solved numerically in a model equilibrium with shifted circular magnetic surfaces. The localization of the eigenmodes, which persist in the magnetohydrodynamic (MHD) second stability region, and the mode structure, are displayed. The role of finite-Larmor radius (FLR) and magnetic drift resonance effects on the growth rate are elucidated. Negative magnetic shear is found to have a stabilizing effect on the mode.