Spatiotemporal Behavior of Drift Waves in LMD-U

Abstract

In the LMD-U linear magnetized plasma, fluctuation measurements have been performed with multi-channel poloidal Langmuir probe arrays to investigate the spatiotemporal behaviors of drift wave turbulence. Twodimensional (poloidal mode number-frequency) power spectrum showed not only fluctuation peaks but also the existence of a broadband fluctuation. The broadband fluctuation developed at high poloidal mode number and high frequency regions and not along the linear dispersion relation curve of drift wave modes. It showed shorter correlation time and poloidal length than the peaked fluctuations. Two-dimensional axial coherence was measured with two poloidal probe arrays separated in the axial direction. The axial coherence was strong for both the broadband fluctuation and peak fluctuations, suggesting the quasi-two-dimensional structure of the drift wave turbulence.

Azimuthal inhomogeneity of turbulence structure and its impact on intermittent particle transport in linear magnetized plasmas

“…By decreasing the neutral pressure, the turbulence regime changes to streamer-type structures. 29,30 A radially movable Mach probe is installed at h ¼ p/4, z ¼ 1.625 m, whose probe head can be scanned from r ¼ 2 cm (r/a ¼ 0.4) to r ¼ 6 cm (r/a ¼ 1.2) on a shot-to-shot basis. The diameter of the probe head is $5 mm, and the probe head houses four probe tips each of which are 0.5 mm in diameter.…”

A Review -Observations of Turbulence and Structure in Magnetized Plasmas

“…For instance, in linear cylindrical devices, such as the Kiel Instruments for Wave Investigation (KIWI) [21] and the Large Mirror Device Upgrade (LMD-U) [22,23] and a toroidal device, TJ-K [24], the Langmuir probe arrays surrounding the plasma surface in the azimuthal direction are used to measure both the spatial and temporal evolution of fluctuations. Figure 3 (a) shows an example of 2D Fourier spectra, S (k θ , ω), measured with a 64 channel azimuthal probe array in an LMD-U linear cylindrical plasma [25][26][27]. Here, the power spectrum can be defined by the ensemble average of the auto-powers asS auto (k θ , ω) = |ũ(k θ , ω)| 2 .…”

Bispectral Analysis of Density and Potential Fluctuations in a High Neutral Density Cylindrical Plasma

“…The envelope modulations of turbulent drift wave fluctuations are observed. Moreover, bispectral analysis is used to identify the mutual interaction of drift waves [9][10][11][12][13]. A convergence study of bispectral analysis results [14] has indicated that a large number of repetitions are required to obtain a precise value for the author's e-mail: kobayashi@riam.kyushu-u.ac.jp bicoherence.…”