Shear damping of two-dimensional drift waves in a large-aspect-ratio tokamak

Abstract

In a uniform plane slab, with shear in the magnetic field, damping of drift waves is due to the outward convection of energy by the wave. It is known, however, that the inclusion of two-dimensional effects, such as toroidal modulation of shear or magnetic field, can inhibit propagation of the wave and so reduce shear damping. This effect is investigated by using a two-dimensional model representing long-wavelength drift waves in a large-aspect-ratio tokamak. It is shown that this two-dimensional problem can be reduced to a one-dimensional eigenvalue equation from which the shear damping can readily be computed. It is confirmed that toroidal effects can annul the shear damping, and some examples are given.