Oscillations of a coronal plasma slab excited by an external source

Abstract

ABSTRACT The dispersive properties of fast oscillations in a coronal plasma slab are studied. These oscillations are assumed to be generated by an external source, located at a finite distance from the slab. It is shown that the problem reduces to examination of the normal modes of a system, consisting of a slab cavity and a finitely distant rigid boundary. The relation that governs the eigenfrequencies of the system is derived. Both the kink and the sausage modes are excited. The main finding indicates that the principal kink mode is trapped not for all axial wavenumbers. It has a non-zero cut-off wavenumber and can exist either as a trapped mode or as a leaky mode. This cut-off tends to zero for infinitely distant sources, in accordance with the well-known result from the normal mode analysis. The expressions for the frequency and damping rate of the leaky principal kink mode are derived. The effect of a finitely distant rigid boundary on the higher transverse-order kink modes and all the sausage modes is found to be only minor, when the distance between the source and the slab is much more than the transverse size of the slab. The applications of the obtained results in coronal seismology are discussed.