The temporal evolution of the kinetic drift-Alfven instability of plasma shear flow

Abstract

The linear non-modal kinetic theory of the kinetic drift-Alfven instability, in the presence of shearing plasma flow, exhibits temporal non-modal amplitude growth with time-increasing growth rate. The drift-Alfven instability develops when the evolving frequencies of the density-gradient-driven drift wave and the kinetic Alfven wave become comparable and mode coupling increases significantly. Because the development of the instability depends on the plasma density gradient, drift-Alfven turbulence may be invoked as a possible turbulence driver in the edge pedestal, limiting the pedestal density gradients during the edge localized modes crash. In contrast to the case of shear-modified electrostatic drift-wave turbulence, the scattering of plasma ions by the shear-modified electromagnetic drift-Alven turbulence does not only suppress the turbulence, but can be responsible for transient increase in the instability's growth rate. The instability, i.e., turbulence, stabilizes when the drift and Alfven wave frequencies eventually become different enough that effective coupling between the two modes ends. So, perpendicular-flow shear can cause the growth rate to increase, decrease, become zero, and become negative as a result of shear's time-changing modification to the frequencies of the drift and Alfven waves.