Radial Structure of Electron Drift Waves in Tokamak Geometry

The radial structure of electron drift waves in a low-pressure tokamak plasma is presented. The ions are cold and an electrostatic approximation for the fluctuating potential is used. It is shown that problem of the radial structure of drift waves in toroidal geometry is amenable to a two-step solution; in the first approximation, the radial structure of the mode is neglected and the problem to be solved is the usual eigenmode equation along the (extended) poloidal angle; in the second approximation, the mode amplitude is expanded in ascending powers of the parameter (k⊥Ln)–1/2, where k⊥ is the magnitude of the lowest-order wavevector and Ln is the radial density scalelength. The implications of these radially-extended drift-type modes for the anomalous cross-field diffusion are discussed.