Characteristics of fluctuations in the equatorial and polar directions of a compact dipole plasma driven at steady state.

The fluctuations in the plasma potential ( V s ̃ ) and electron density ( N e ̃ ) are measured in the steady-state dipole plasma confined in a spherical vacuum chamber using a single permanent dipole magnet. Measurements are made from a radial distance r = 0.5–17 cm, from the surface of the magnet in the equatorial (θ = 90 °) and polar (θ = 180 °) directions, using a 4-pin probe setup, and have been characterized by power spectra, cross-phase, cross-coherence, induced transport, and energy spectra. The fluctuations are stronger near the surface of the dipole magnet for θ = 90 ° , thereafter their magnitude decreases gradually with the radial distance. However, a peaked profile of potential fluctuations with the peak around r = 9 cm is observed for θ = 180 °. The locations of strong fluctuations are around the locations of smaller values of the electron neutral collision frequency. Frequency-resolved power spectra show that the fluctuations in the dipole plasma, predominantly, belong to the very low-frequency range. The values of cross-phase (≤ 45 °) and | V s ̃ / T e | / | N e ̃ / N e | ≤ 1 indicate the presence of drift wave instability in both planes, where T e and N e are equilibrium values of the electron temperature and density. The radial variation of fluctuation-induced electron flux ( Γ r ) verifies the "inward diffusion" of electrons in the equatorial plane. [ABSTRACT FROM AUTHOR]