Abstract
The cesium magnetoplasma was chosen as the ideal environment in which to study what is perhaps the best known of all plasma instabilities, the helical instability. Extant theories are shown to make assumptions regarding electron density profiles that may not represent actual conditions in laboratory plasmas. The theoretical dependencies of the onset criteria for the helical instability is investigated to determine the sensitivity to a variety of radial electron density profiles.In order to compare the results of these measurements with available theories for the helical instability, experimental values for the electron mobility were obtained by measuring the Hall potential developed between probes placed in the cesium discharge. These measurement were then compared to Langmuir probe measurements in cesium. Measurements were made of critical values of the onset criteria for this instability, in a cylindrical cesium plasma, in a longitudinal magnetic field. The experimental values for critical electric and magnetic fields at onset together with experimental values of the electron mobility were then compared with theoretical predictions.It is shown that detailed knowledge of the radial electron density profile in a cylindrical plasma, in a longitudinal magnetic field, is crucial to accurately predicting the critical onset criteria for the helical instability in terms of axial electric field axial magnetic field and wavenumber.