Propagation of axisymmetric Trivelpiece-Gould mode along vortex columns generated by diocotron instability

Abstract

A high-frequency (HF) oscillation has been observed to propagate along magnetic field lines with an axisymmetric profile extending over multiple columns of magnetized pure electron plasma which undergo two-dimensional vortex motions. The observed frequency is a few hundred times higher than the rotation frequency of the vortices and varies in time as the density distribution of electrons deforms from an unstable hollow profile into vortex columns and approaches a single-peaked distribution. Experimental examinations reveal that the HF oscillation is excited by the gate pulse applied to prepare the initial profile and that the oscillation does not influence the subsequent dynamics of vortex columns. Further examinations including detailed observations and theoretical analyses indicate that the HF oscillation represents a profile-dependent eigenfunction of the Trivelpiece-Gould mode wave that consists of a dominant axisymmetric component and small fractions of higher azimuthal modes associated with the density distribution separated into columns.