Wobble motion on field-reversed configuration plasmas

Abstract

A wobble motion on a field-reversed configuration plasma is investigated in detail. It is found from magnetic and optical measurements of the wobble motion that a few magnetic islands appear inside a separatrix at the formation phase and merge with each other at the axial contraction phase. Due to the radial and azimuthal asymmetries of the merging plasmas, the wobble motion is triggered. To assist the symmetrical formation of the plasma, conducting rings are installed near the ends of the theta-pinch coil. Using the effect of the conducting rings, the amplitude of the wobble motion is controlled to approximately one-half that without using the conducting rings and the extreme degradation of particle confinement time is not observed. An analysis of the plasma affected by a restoring force of open field lines well explains an experimental result that the period of wobble motion depends on the square root of mass density. © 2005 American Institute of Physics.