Kinetic theory of electromagnetic geodesic acoustic modes

Abstract

The electromagnetic effects on geodesic acoustic modes due to electron parallel motion are investigated by employing the kinetic theory and appropriate expansion of the electron distribution function. The existence of several electromagnetic modes involving average geodesic curvature with different frequencies and polarization are revealed. It is shown that there are two Alfven side-band modes with different polarizations which also have different values of adiabatic indices due to average geodesic compressibility. The dispersion corrections to the eigen-frequencies of geodesic acoustic and related electromagnetic modes are investigated. It is shown that the dispersion due to electron dynamics is different depending on whether the electron response is adiabatic or hydrodynamic, i.e. depends on the ratio of the parameter, . It is noted that for m = n = 0 only the hydrodynamic regime is possible, . Principal electron effects leading to the dispersion involve a finite ion-sound Larmor radius , electron inertia and a finite electron magnetic drift frequency, .