Coupled Surface Flute Waves Propagating in Current-Carrying Plasma Waveguides

Abstract

To produce and sustain gaseous plasmas in various laboratory devices one can often apply direct electrical currents, for example, in magnetically confined fusion plasmas in tokamaks or for plasma production in various technological devices. Possible flowing of charged plasma particles has not been taken into account in the previous Chapter, which is devoted to the study of the basic features of transverse eigen modes propagating in simple models of cylindrical waveguides with plasma filling. That is why in the present Chapter the influence of an axial electric current on the dispersion properties of eigen flute modes propagating in various cylindrical waveguide structures with plasma filling is under consideration. The plasma is assumed to be sufficiently dense so that the electron cyclotron frequency is less than the electron plasma frequency. However unlike in Chap. 2, here the plasma is affected by an azimuthal magnetic field, which is produced by the axial electric current. The value of this axial electric current is supposed to be sufficiently small so that either the azimuthal component of the external magnetic field is much less than its axial component or the cyclotron frequency due to the azimuthal magnetic field is much less than the eigen frequency of the flute modes in the case if there is no axial magnetic field. In this case Maxwell equations cannot be solved separately for any independent mode. Therefore the dispersion relation of flute X- and O-modes becomes a coupled form. This leads to the appearance of new wave phenomena compared with Chap. 2, such as mode coupling, forbidden bands in the frequency spectrum of the coupled flute modes, mode damping or radiation of their power out of the waveguide.