Determination of Spatiotemporal Structure of Fluctuations by Statistical Averaging Method

Abstract

Spatiotemporal structure of fluctuation with 11 kHz excited in a linear magnetized plasma was observed in details by applying pattern recognition method based on statistical averaging. Statistical behaviors of instantaneous period of the fluctuation and the temporal behavior of the radial profile of the fluctuation are clarified. Two-dimensional structure of the fluctuation is reconstructed and distortion of the wave-front of the fluctuation was inferred.

Observation of spatiotemporal structures of temperature fluctuations by using of a statistical phase detection method in a linear magnetized plasma

“…Figures 12 (a the m = 1 mode, the m = 4 component should disapper. These results indicate m = 1 is nonlinearly coupled with the m = 4 mode and agree with bicoherence analysis [13]. Te / Te contains more harmonics components than ñe /n e .…”

“…Here, ñe /n e was evaluated as ñe /n e ≈ Ĩis / Īis − 0.5 × Te / Te We succeeded to observe electron temperature fluctuations of the m = 4 mode. Conditional averaging is also applied to ion saturation current measurement with the same trigger obtained by the template method [13]. A comparison of the normalized waveforms obtained from conditional sampling and averaging is shown in figure 9.…”

“…Therefore, a method to detect emergence timings of not only spiky but also sinusoidal-like waveforms is required. To determine the emergence timings of sinusoidal-like waveforms, we used s statistical phase detection method, the template method [12,13]. The template method determines the fluctuation emergence timings based on the peaks of crosscorrelation between the original signal and the template waveform obtained through the iteration process.…”

Comparison of Conditional Average Using Threshold and Template Methods for Quasi-Periodic Phenomena in Plasmas

“…In this paper, we call this author's e-mail: kin.fumiyoshi@qst.go.jp a) Current affiliation: National Institutes for Quantum and Radiological Science and Technology, Naka 311-0193, Japan technique the threshold method. The other technique developed recently is called the template method [7,8], in which the clocks are determined as the times when the cross-correlation between the template and the signal is sufficiently high, in other words, when the signal resembles to some degree of the standard pattern defined as 'template'. This article presents the results of conditional averaging applied on the intermittent bursts observed during the I-mode plasma of ASDEX Upgrade (AUG) [9][10][11], and shows the excellent features of the template methods by the comparison to the threshold methods.…”

Sparsity-Promoting Dynamic Mode Decomposition of Plasma Turbulence

“…Usually, ensemble averaging is replaced by time averaging [6], which can mask the non-stationarity of the signals. Actually, structure in plasma turbulence varies in time [7], and thus new analysis tools, which can extract the non-stationary spatiotemporal structure of the turbulence, are required. Here we apply a dynamic mode decomposition (DMD) analysis to signals of turbulence in a magnetized laboratory plasma.…”