Structure of short-wavelength drift modes and transport in a toroidal plasma

Abstract

Short-wavelength fluctuations, such as electron and ion drift waves, may be one cause of anomalous transport in toroidal plasmas. The purpose of this paper is to establish the radial structure of these modes and to clarify some discrepancies in the literature. The conventional form of toroidal drift modes can occur only at isolated plasma radii and are unlikely to be the source of a universal transport. However, a more recently described class of electron and ion drift modes can occur at all plasma radii. They have a structure consistent with an anomalous transport exhibiting the Bohm scaling with magnetic field and decreasing with plasma rotation.

Geometric stabilization of the electrostatic ion-temperature-gradient driven instability. I. Nearly axisymmetric systems

“…[35]. Similar results apply in the context of driftwave turbulence [32,36,37], see Fig. (6) of Ref [37].…”

“…Radially global structures of drift-wave-like linear modes [31,32] (as the ITG mode) generally form on time scales too long to be observed before turbulent radial decorrelatation would suppress them. On the other hand, fast variations of equilibrium quantities in y (α) are mostly given by the machine design, they are externally imposed, and they are in fact likely to manifest even nonlinearly [17,33] .…”

Drift waves and transport

“…The toroidal theory with sheared flow requires an extension of the standard ballooning transformation (Pegoraro, 1989;Miller and Waltz, 1994;Kim et al, 1996). The Taylor, Wilson, and Connor (1996) analysis shows that sheared rotation annuls the toroidal coupling between perturbations associated with neighboring magnetic surfaces, so that the problem closely resembles that of the modes in a cylinder than in a torus. In the cylindrical limit the reduction of the growth rate is a function of the ratio of EϫB flow shear to magnetic shear SϭL n /L s .…”

Sheared rotation effects on kinetic stability in enhanced confinement tokamak plasmas, and nonlinear dynamics of fluctuations and flows in axisymmetric plasmas

“…An alternative w ould be to average the eigenfrequency over 0 0 2 , as speci ed in Ref. 21. However, a better prescription could in principle be determined as follows: One-dimensional (ballooning representation) and two-dimensional calculations for toroidal drift modes have been compared for the older rotation model of Refs.…”