Fluctuations and turbulence in an electric field bumpy torus plasma

Abstract

In this experiment, strong radial electric fields were imposed along the minor radius of a steady-state bumpy torus plasma by biasing it with electrodes maintained at kilovolt potentials. Digitally implemented spectral analysis techniques were used to experimentally investigate the characteristics of the fluctuations of plasma number density and electrostatic potential below the ion plasma and ion cyclotron frequencies. The dispersion relation between ω and k for azimuthally propagating waves was determined experimentally, and, when linear, was consistent with the E/B drift velocity. Above 100 kHz, the power spectra of both density and potential fluctuations obeyed a power law of the form P(ω) α ω−p. The spectral index p of this plasma turbulence assumed values which varied with operating conditions. The fluctuations of density and potential ranged from highly coherent rotating spokes, to highly turbulent conditions with a Gaussian distribution in amplitude.