Transport Induced by Large Scale Convective Structures in a Dipole-Confined Plasma

Grierson, B. A.; Mauel, M. E.; Mw, Worstell; Klassen, Mikhail

doi:10.1103/physrevlett.105.205004

Cited by 8 publications

(9 citation statements)

References 20 publications

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“…These intermittent fluctuations resemble previous observations of dipole plasma turbulence 28 where global diagnostics showed the bursty fluctuations to be slowly rotating field-aligned filaments that move rapidly in radius.…”

Section: Observation Of Turbulent Transportsupporting

confidence: 66%

“…27 Local turbulent transport is intermittent, consisting of inward and outward moving plasma filaments that are field-aligned and can move radially at speeds reaching 10% of the sound speed. 28 The PDF of the radial particle transport is non-Gaussian with high kurtosis and skewness. Furthermore, the PDF measured in a dipole-confined plasma torus resembles the probability distribution measured in the same way at the edges of tokamaks and stellarators.…”

Section: Discussion and Summarymentioning

confidence: 99%

“…The fluctuations observed in the large LDX experiment resemble the fluctuations observed in a smaller magnetic dipole experiment where the spatial and temporal structures of the fluctuations are characterized as chaotically rotating flute-like modes. 27,28 While not on-topic to the investigations reported in this paper, the largest low-frequency mode is axisymmetric (m ¼ 0) with a frequency near 100 Hz. This global mode is described in Ref.…”

Section: Low-frequency Turbulent Fluctuationsmentioning

confidence: 99%

“…28 The density profile evolution determined the inward particle flux to equal the product of a quasilinear diffusion coefficient, D ¼ R 2 h e E 2 u is cor , with the gradient of the particle flux-tube number, @ðndVÞ=@w. Whole plasma imaging of interchange convection was seen to be "bursty," consisting of outward moving and field-aligned dense "filaments" and inward moving less-dense "filaments".…”

Section: Observation Of Turbulent Transportmentioning

confidence: 99%

“…Broadband electrostatic interchange turbulence develops consisting of many global modes with chaotic amplitudes and phases 27 that cause intermittent transport. 28 Although the energy flux is always outward, theory and simulation show that the radial particle and temperature flux can be either inward or outward depending upon the ratio of temperature to density gradient scale lengths, g d ln T e =d ln n. When g ¼ ðc À 1Þ ¼ 2=3, the MHD condition of marginal stability to pressure-driven interchange motion coincides with the "stationary" profile, where both @ðndVÞ=@w % @ðpdV c Þ=@w % 0. For a "stationary" profile at marginal stability, interchange motion leaves the profile unchanged.…”

Section: Introductionmentioning

confidence: 99%

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Turbulent fluctuations during pellet injection into a dipole confined plasma torus

et al. 2017

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We report measurements of the turbulent evolution of the plasma density profile following the fast injection of lithium pellets into the Levitated Dipole Experiment (LDX) [Boxer et al., Nat. Phys. 6, 207 (2010)]. As the pellet passes through the plasma, it provides a significant internal particle source and allows investigation of density profile evolution, turbulent relaxation, and turbulent fluctuations. The total electron number within the dipole plasma torus increases by more than a factor of three, and the central density increases by more than a factor of five. During these large changes in density, the shape of the density profile is nearly “stationary” such that the gradient of the particle number within tubes of equal magnetic flux vanishes. In comparison to the usual case, when the particle source is neutral gas at the plasma edge, the internal source from the pellet causes the toroidal phase velocity of the fluctuations to reverse and changes the average particle flux at the plasma edge. An edge particle source creates an inward turbulent pinch, but an internal particle source increases the outward turbulent particle flux. Statistical properties of the turbulence are measured by multiple microwave interferometers and by an array of probes at the edge. The spatial structures of the largest amplitude modes have long radial and toroidal wavelengths. Estimates of the local and toroidally averaged turbulent particle flux show intermittency and a non-Gaussian probability distribution function. The measured fluctuations, both before and during pellet injection, have frequency and wavenumber dispersion consistent with theoretical expectations for interchange and entropy modes excited within a dipole plasma torus having warm electrons and cool ions.

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Section: Observation Of Turbulent Transportsupporting

confidence: 66%

Section: Discussion and Summarymentioning

confidence: 99%

Section: Low-frequency Turbulent Fluctuationsmentioning

confidence: 99%

Section: Observation Of Turbulent Transportmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Turbulent fluctuations during pellet injection into a dipole confined plasma torus

et al. 2017

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Local regulation of interchange turbulence in a dipole-confined plasma torus using current-collection feedback

2015

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Turbulence in plasma confined by a magnetic dipole is dominated by interchange fluctuations with complex dynamics and short spatial coherence. We report the first use of local current-collection feedback to modify, amplify, and suppress these fluctuations. The spatial extent of turbulence regulation is limited to a correlation length near the collector. Changing the gain and phase of collection results in power either extracted from or injected into the turbulence. The measured plasma response shows some agreement with calculations of the linear response of global interchange-like MHD and entropy modes to current-collection feedback. V C 2015 AIP Publishing LLC.

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Imaging free-falling particles for multipoint measurement of plasma fluctuations

Roberts

Mauel

Abler

et al. 2015

Review of Scientific Instruments

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The measurement of plasma fluctuations by insertable probes is sometimes limited by the perturbation of the probe on the plasma, and some non-invasive diagnostics such as photodiode arrays can only measure integrated values. In this paper, we introduce a new approach to plasma fluctuation measurement using small, free-falling particles imaged with a fast camera to provide simultaneous multipoint measurement of visible light emissions surrounding each particle. We find that the fluctuations measured in this manner are in agreement with existing diagnostics, and the particle signals are correlated to those measured on inserted floating potential probes. Signals from multiple particles demonstrate an application of multipoint measurement of the plasma spatial structure and coherence.

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Transport Induced by Large Scale Convective Structures in a Dipole-Confined Plasma

Cited by 8 publications

References 20 publications

Turbulent fluctuations during pellet injection into a dipole confined plasma torus

Turbulent fluctuations during pellet injection into a dipole confined plasma torus

Local regulation of interchange turbulence in a dipole-confined plasma torus using current-collection feedback

Imaging free-falling particles for multipoint measurement of plasma fluctuations

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