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.

Phenomenological Classification of Turbulence States in Linear Magnetized Plasma PANTA

“…The parameter scan experiments were conducted in a linear magnetized plasma PANTA [23,24]. As shown in Fig.…”

“…where b 2 (r, f, f ) is the auto bicoherence of the ion satu- ration current fluctuation in which the matching condition f = f ± f is satisfied [6,24,29]. The higher total squared bicoherence at high p n and intermediate B region corresponds to the peak in the fluctuation power.…”

Two-dimensional bispectral analysis of drift wave turbulence in a cylindrical plasma

“…32 A 64-channel poloidal Langmuir probe array 33 has been installed to take 2D measurements in poloidal wave number and frequency, in order to clarify the structure of nonlinear coupling in drift wave turbulence. The measurements have provided several interesting results, [34][35][36] such as the first experimental identification of streamers. In this paper, we present a full description of the results from the 2D bispectral analysis, e.g., the existence of nonlinear coupling between peaks and broadband fluctuations.…”

“…The formation processes of drift wave turbulence were studied on KIWI. 7 In the case of LMD-U, the excited mode changes into drift wave turbulence when the magnetic field is raised above 0.04 T or the argon pressure is reduced to less than 0.4 Pa. 35 The spatiotemporal pattern of the fluctuation is measurable with the 64-channel poloidal probe array. The waveform of nonturbulent plasma without turbulence is a periodical pattern.…”

“…As is reported in Ref. 35, the radial power spectrum profile of the normalized ion saturation-current fluctuation was measured using a radially mobile probe. The fluctuations above 2 kHz have a maximum amplitude around r = 30 mm, where the density gradient is steep.…”