Radial structure of electron drift waves and anomalous transport in the edge plasma

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 the problem of the radial structure of drift waves in toroidal geometry is amenable to a two-step solution; in 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 second approximation, the mode amplitude is expanded in ascending powers of the parameter (k Ln)ʹ-1/2 where k is the magnitude of the lowest-order wavevector and Ln is the radial density scale length. It is shown that the radial structure of drift-type modes can depend strongly on the magnetic shear and the scalar magnetic curvature. Numerical calculations for plasma parameters relevant to the edge region of medium-size tokamaks are presented.