Alfven Wave Excitation in a Cavity with a Transverse Magnetic Field

Abstract

A transversely magnetized cylindrical plasma model with an internal rod conductor is used to approximate the FIVA internal ring device of Spherator type with a purely poloidal magnetic field. It is shown that an excitation asymmetry along the plasma column, i.e. with a wave number k2 ≠ 0, introduces a coupling between the magnetoacoustic and shear Alfven waves in the frequency range ω ≪ ωci. The introduction of an equilibrium mass motion along the plasma cylinder introduces a flow continuum. Simultaneously the Alfven resonance frequency becomes Doppler shifted. The experimental observations indicate that cavity modes do not build up in the FIVA device in the case of nonsymmetric excitation. If on the other hand the exciting structure becomes symmetric, i.e. with k2 = 0, the magnetoacoustic resonances become excited. The resulting Q values are rather low which indicates that the coupling to the shear wave through the Hall electric field cannot be neglected