Phenomenological Classification of Turbulence States in Linear Magnetized Plasma PANTA

Abstract

Changing the experimental conditions such as the neutral pressure and the magnetic field strength provides a drastic change in the turbulence states in linear magnetized helicon plasmas. In order to define the turbulence states and their occurrence region a throughout parameter scan in the two-dimensional parameter space was performed. The classification of the turbulence states is carried out phenomenologically based on the turbulence spectrum and the waveform.

Reconstruction of Time Series Observed in Linear Magnetized Plasma PANTA via a Machine Learning Algorithm

“…Due to the periodicity, statistical characteristics of time series data obtained by each probe are similar. The data used in this study show the formation of the streamer [7], which is an azimuthal bunching of fluctuation. In this study, the drift waves and the nonlinear quasimode (mediator), which has much longer time scale than that of the drift wave, coexist.…”

“…1 and 2 (a), reconstructions by the linear interpolation with N = 1, 2 are fairly accurate, while correlation coefficients decrease with increasing N(≥ 3). It is because the distance between two probes (coarse-graining scale 2N + 1) is longer than the wavelength of the drift waves [7] when N ≥ 3. On the other hand, reconstructions by the random forest (black marks) with six probes are much better than those by the simple linear interpolation.…”

Impact of helium neutral gas puff on plasma turbulence in linear magnetized argon plasmas

“…7 However, nonlinear mesoscale fluctuating structures, such as zonal flows and streamers, formed in a saturated drift wave turbulence system are found to vary according to the ion-neutral collision frequency or the neutral pressure. 6,[8][9][10] Nonlinear fluid simulation involving the neutral particle dynamics was recently implemented for calculating nonlinear turbulence evolution in the realistic experimental situation. 11 By taking into account the ionization process of neutrals in the ion fluid equation, a new instability can be derived as well.…”

“…21 In order to experimentally assess the impact of the neutrals on the turbulence and flow dynamics, neutral pressure scan experiments are occasionally performed in basic devices as one of the most simple operations. 2,9,10,14 In the case of PANTA linear magnetized plasma, increasing the neutral pressure leads to not only an increase in the neutral density but also concomitant growth of the electron density gradient. 10 Therefore, not only damping but also the growth rate of the drift wave is simultaneously varied, which is unsuitable for interpretation of the background physics.…”

Ion Mass Dependence of Resistive Drift Wave Turbulence in Cylindrical Plasmas

“…Since turbulence structures have great influence on plasma transport [1], understanding of their formation mechanism is important for the control of fusion plasmas. Experiments in linear device PANTA have shown that there exist several types of nonlinear structures generated by drift wave instabilities, depending on parameters [2], such as streamers [3], zonal flows and solitary drift waves [4]. Numerical simulations also have shown structural bifurcation [5,6].…”