Experimental Study of Drift Wave Turbulence in Linear Plasmas

Abstract

Linear plasmas allow multi-point, low-temperature measurements with Langmuir probes. We measured ion saturation-current fluctuations of a Large Mirror Device-Upgrade linear plasma using a poloidal Langmuir probe array. By varying the discharge conditions, the spatiotemporal behavior showed a change from a coherent sine wave to a turbulent waveform through a periodic, modulated sine wave. The two-dimensional (poloidal wave number and frequency) power spectrum for each regime showed a single fluctuation peak, a peak and its harmonics, and a number of peaks in the poloidal wave number-frequency space. Bi-spectral analysis was performed for the turbulent regime, and showed the existence of nonlinear couplings among fluctuation peaks and broadband components.