The collisionality dependence of intermittency level in drift-wave turbulence in the stellarator TJ-K

Garland, S.; Reuther, K.; Ramisch, M.; Mänz, P.

doi:10.1063/1.4991609

Cited by 7 publications

(7 citation statements)

References 45 publications

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“…studied the effect of collisionality on the intermittency of the density and potential fluctuation in the TJ-K stellarator (Garland et al. 2017). In those stellarator experiments the collisionality was varied from the collisionless drift-wave regime to resistive drift waves using different plasma species.…”

Section: Discussionmentioning

confidence: 99%

“…Moreover, this is the region of the plasma where the impact of neutrals cannot be neglected (Fülöp, Catto & Helander 1998;Omotani et al 2016). The complex two-dimensional geometry in a tokamak with poloidal asymmetries, magnetic field (B-field) curvature and gradients makes the study of fundamental drift-wave turbulence more complicated, whereas linear machines such as the Large Plasma Device (LAPD) provide the ideal conditions to measure the changes in drift-wave turbulence and plasma parameters (Gekelman et al 2016).…”

Section: Introductionmentioning

confidence: 99%

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Impact of the electron density and temperature gradient on drift-wave turbulence in the Large Plasma Device

Perks

Mordijck²,

Carter³

et al. 2022

J. Plasma Phys.

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In this paper we present an experimental study of edge turbulence in the Large Plasma Device at UCLA. We utilize a scan of discharge power and prefill pressure (neutral density) to show experimentally that turbulent density fluctuations decrease with decreasing density gradient, as predicted for resistive drift-wave turbulence (RDWT). As expected for RDWT, we observe that the cross-phase between the density and potential fluctuations is close to 0. Moreover, the addition of an electron temperature gradient leads to a reduction in the amplitude of the density fluctuations, as expected for RDWT. However, counter to theoretical expectations, we find that the potential fluctuations do not follow the same trends as the density fluctuations for changes either in density gradients or the addition of a temperature gradient. The disconnect between the density and potential fluctuations is connected to changes in the parallel flows as a result of differences in the prefill pressure, i.e. neutral density. Further analysis of the density and potential fluctuation spectra show that the electron temperature gradient reduces the low frequency fluctuations up to $10 \,{\rm kHz}$ and the introduction of a temperature gradient leads to an unexpected ${\sim }{\rm \pi}$ shift of the density–potential cross-phase at ${\sim }10\,{\rm kHz}$ , while maintaining the typical resistive drift-wave cross-phase at lower frequencies. These experiments partly confirm existing knowledge on resistive drift-wave turbulence, but also introduce new observations that indicate a need for dedicated nonlinear three-dimensional turbulence simulations that include neutrals.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Impact of the electron density and temperature gradient on drift-wave turbulence in the Large Plasma Device

Perks

Mordijck²,

Carter³

et al. 2022

J. Plasma Phys.

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“…In the adiabatic limit of drift-wave turbulence, where the collisionality is very low, the density field is strongly coupled to the electrostatic potential resulting in electrically unpolarised density perturbations. A previous study 11 has shown that a decoupling of density and potential in drift-wave turbulence via increased collisionality leads to intermittency in the density fluctuations. It is thus reasonable to assume that a magnetic field curvature driven polarisation of density perturbations could have a similar effect on the intermittency of the turbulence.…”

Section: Introductionmentioning

confidence: 94%

“…The main feature in the EHW 1 simulation poloidal µ n profile is a higher intermittency parameter on the low-field side, where κ n < 0 as compared to at θ = π, where κ n > 0. This can be explained by the decoupling of the density and potential fluctuations through the curvature terms in equations 6 when the normal curvature is negative, in a similar way to which the density-potential coupling is influenced by the collisionality parameter in the classic HW model 11,12 . However, the coupling terms in the EHW model, κ n ∂ y (φ − n) and κ g ∂ x (φ − n), in- volve taking the spatial gradients ∂ x and ∂ y of the term (φ − n).…”

Section: Extended Hasegawa-wakatani Simulationsmentioning

confidence: 99%

The influence of magnetic field curvature on intermittency in drift-wave turbulence in the stellarator TJ-K

2020

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The influence of magnetic field curvature on the intermittency in density and potential fluctuations in driftwave turbulence has been investigated in the stellarator TJ-K in the framework of an extended Hasegawa-Wakatani model. A structure function analysis was used to estimate the intermittency level of poloidally resolved drift-wave turbulence measurements of a deuterium plasma in TJ-K. Potential fluctuations were found to be broadly self-similar, whereas density fluctuations were found to be more intermittent in the region with negative normal and positive geodesic curvature. This behaviour could be understood by comparing the data to two-dimensional extended Hasegawa-Wakatani simulations which retain gradients in the magnetic field strength, giving rise to curvature effects. The model is able to reproduce the trends in the experimental data if both normal and geodesic curvature effects are accounted for, as well as the local anisotropy of turbulent length scales. The analysis indicates the importance of local magnetic geometry as a factor in the decoupling of density and potential fluctuations, leading to intermittency in drift-wave turbulence.

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“…[5], the authors showed that turbulence fluctuations have non-Gaussian characteristics, while the radial flux of plasma density is similar to Bohm diffusion. Garland et al [6] presented a study investigating the influence of collisionality on intermittency in drift-wave turbulence using both numerical and experimental approaches, the latter for the TJ-K stellerator; they showed an increase in intermittency with increasing collisionality for density fluctuations. The study in [7] revealed the importance of considering local curvature properties as a factor in the decoupling of density and potential fluctuations leading to intermittency in drift-wave turbulence.…”

Section: Introductionmentioning

confidence: 99%

Transport, flow topology and Lagrangian conditional statistics in edge plasma turbulence

Kadoch¹,

del‐Castillo‐Negrete²,

Bos³

et al. 2022

Preprint

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Lagrangian statistics and particle transport in edge plasma turbulence are investigated using the Hasegawa-Wakatani model and its modified version. The latter shows the emergence of pronounced zonal flows. Different values of the adiabaticity parameter are considered. The main goal is to characterize the role of coherent structures, i.e., vortices and zonal flows, and their impact on the Lagrangian statistics of particles. Computationally intensive long time simulations following ensembles of test particles over hundreds of eddy turnover times are considered in statistically stationary turbulent flows. The flow topology is characterized using the Lagrangian Okubo-Weiss criterion, and the flow can thus be split into topologically different domains. In elliptic and hyperbolic regions, the probability density functions (pdfs) of the residence time have self-similar algebraic decaying tails. However, in the intermediate regions the pdfs do exhibit exponentially decaying tails. Topologically conditioned pdfs of the Lagrangian velocity, and acceleration and density fluctuations are likewise computed. The differences between the classical Hasegawa-Wakatani system and its modified version are assessed and the role of zonal flows is highlighted. The density flux spectrum which characterizes the contributions of different length scales is studied and its inertial scaling is found to be in agreement with predictions based on dimensional arguments. Analyzing the angular change of particle tracers at different time scales, corresponding to coarse grained curvature, completes the study and the multiscale geometric statistics quantify the directional properties of the particle motion in the different flow regimes.

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The collisionality dependence of intermittency level in drift-wave turbulence in the stellarator TJ-K

Cited by 7 publications

References 45 publications

Impact of the electron density and temperature gradient on drift-wave turbulence in the Large Plasma Device

Impact of the electron density and temperature gradient on drift-wave turbulence in the Large Plasma Device

The influence of magnetic field curvature on intermittency in drift-wave turbulence in the stellarator TJ-K

Transport, flow topology and Lagrangian conditional statistics in edge plasma turbulence

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