Wave‐particle transport from density drift instabilities: A comparison of local and nonlocal theories

Abstract

A plasma density gradient perpendicular to an ambient magnetic field is unstable to the growth of electrostatic waves. The objective of this paper is to describe the rate at which these density drift instabilities transport plasma across the magnetic field lines. This objective is accomplished as follows: The plasma density irregularity is represented as a Fourier series. Using linear Vlasov theory, the nonlocal dispersion equation is derived, relating the Fourier amplitudes to the eigenvalues (i.e., wave frequencies and growth rates) for the electrostatic fluctuations. For each complex eigenvalue, an electrostatic eigenmode is computed. These eigenmodes grow to saturation and are summed, yielding the total electrostatic turbulence. The flux of plasma across the magnetic field lines is computed from the turbulence. The transport derived from the nonlocal theory is compared with that derived by using the less complicated local approximation. Wave‐particle transport based on the local approximation is shown to be valid only in regions where variations in the density gradient are small.