Spectrum of low-frequency, nonaxisymmetric oscillations in a cold, current-carrying plasma column

Abstract

The spectrum of low‐frequency, m= ±1 oscillations in a cold, collisionless, cylindrical plasma comprises the frequencies of the lowest radial eigenmodes and the surface modes of the fast magnetosonic wave, all the global eigenmodes of the Alfvén wave (ion‐cyclotron wave), and the Alfvén continuum. The spectrum of a homogeneous, currentless plasma cylinder is obtained from an analytical dispersion relation. This spectrum is compared with numerically obtained spectra of nonuniform plasmas with and without axial current. The connection of the magnetohydrodynamic (MHD) kink and internal kink instabilities with the global eigenmodes of the Alfvén wave is evidenced. Among all the modes of the magnetosonic wave which have frequencies in the Alfvén continuum, the (m= −1, k<0) ‐surface mode is the best candidate for antenna–plasma coupling because its conversion layer is located well into the plasma interior.