Identification of Quasi-Periodic Nonlinear Waveforms in Turbulent Plasmas

Abstract

A new method is presented for identifying waveforms of fluctuations in turbulent plasmas. The method is based on heartbeat analysis in which the convolution of a waveform is obtained by employing the phase tracking method. Phase tracking is performed by correlating raw time-series data with a template waveform; the template is evaluated through iteration procedure. The method is applied to fluctuations in a PANTA plasma, and the nonlinear waveform and its distribution of periods are obtained. The identification of nonlinear waveforms is an essential task in the study of turbulent plasmas. The waveform, which includes information on higher harmonics (i.e., amplitude as well as phase), is the fundamental information that reflects nonlinearity in plasmas. A standard experimental approach is the convolution (i.e., conditional averaging) of time-series data. This approach has been applied to turbulent plasmas in the LMD-U device, and this has led to identification of large-amplitude solitary wave structures [1]. However, simple convolution within a prescribed period is not always sufficient because the period of oscillations can change over time. Intermittent variations in fluctuation periods, which often occur in turbulent plasmas, require a new method for identifying nonlinear waveforms.In this article, a new method is presented for identifying the waveforms of perturbations in turbulent plasmas. Convolution of a waveform is performed by employing the phase tracking method, which is based on heartbeat analysis [2]. The method is applied to fluctuations in PANTA plasmas [3], and the nonlinear waveform and its distribution of periods are obtained.At this point, we explain the new method. Figure 1 (a) illustrates a time series of observed fluctuations for a floating potential, which was observed in PANTA plasmas [1]. In this case, the perturbation is quasi-periodic, as can be

Eddy, drift wave and zonal flow dynamics in a linear magnetized plasma

“…A local peak of density bump rotates in the azimuthal direction quasi-periodically. The time at the peak of density bump in each period, t 0 , is detected with the azimuthal probe array at r 0 = 4 cm by using the template method 28 . Then the delay time for i -th period, τ , is defined as τ = t − t 0 ( i ).…”

Determination of Spatiotemporal Structure of Fluctuations by Statistical Averaging Method

“…The template is converged after 3 iterations. More iterations are required in some cases [10]. We assume that high probability timing of appearance of the template is given by local maximum of the C j (t) and then the trigger function is given by a delta function ( i δ(t − t i ), where t i is the time-to-peak of C j (t)).…”

Measurement of Electron Density and Temperature Using Laser Thomson Scattering in PANTA

“…Measurement of turbulent n e and T e fluctuations is important to identify the instability in plasma and evaluate the particle and heat transport driven by the turbulence. For time-resolved measurement, the conditional averaging technique can be used [24]; that is, in PANTA, a strong quasi-coherent mode is excited in the low-frequency region. These low-frequency components of T e and n e are extracted by the conditional averaging technique.…”