Characterization of instability regimes in the Helimak, a simple magnetic torus

Plasma instability regimes are investigated in the Texas Helimak, a toroidal magnetic confinement device that acts as a physical approximation of the theoretical sheared cylindrical slab. The transition from a regime dominated by the ideal interchange instability to one dominated by drift waves is investigated through experimental measurements of the parallel wavenumber, k [parallel symbol], and other statistics, such as the measurement of applicable power spectra. It is shown that the ideal interchange instability dominates in Helimak plasma at high pitch while drift waves dominate at low pitch. Investigations relative to the effects of an applied bias voltage, both positive and negative, are also carried out. In these it is shown that the application of bias greatly influences both the nature and the amplitude of the turbulence.