Azimuthal Plasmoid Motion in a Coaxial Source with Bz Bias

Abstract

Photographic evidence is presented for the presence of an azimuthal component of the plasmoid motion in a coaxial source of small aspect ratio when operated with an applied Bz field comparable in magnitude to the mean, self-induced Bθ field. The series of displaced images obtained suggests that the rotation is of the correct sense, and that restrikes of the source rotate in alternate directions with the current reversal in the source every half-wave. Photographs taken without bias field confirm the fact that the plasmoid does not form a continuous torus, and the theoretical consequences of this upon the simple hydromagnetic model are examined. This model is used also to derive an approximate equation of azimuthal motion which predicts an amount of rotation about three times larger than that observed. The amount of rotation does, nevertheless, scale with the bias field strength, as predicted by the model.