Structure and motion of edge turbulence in the National Spherical Torus Experiment and Alcator C-Mod

Zweben, S. J.; Maqueda, R. J.; Terry, J. L.; Munsat, T.; Myra, J. R.; D’Ippolito, D. A.; Russell, D. A.; Krommes, John A.; LeBlanc, B.; Stoltzfus-Dueck, T.; Stotler, D.P.; Williams, Kyron; Bush, C. E.; Maingi, R.; Grulke, O.; Sabbagh, S.A.; White, A. E.

doi:10.1063/1.2177132

Cited by 69 publications

(64 citation statements)

References 30 publications

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“…[1][2][3][4][5] These filaments appear as blobs of plasma in the plane perpendicular to the magnetic field and may propagate across the SOL to the main chamber walls. [6][7][8][9][10] The average SOL plasma density and the particle and heat fluxes due to the radial motion of plasma filaments depend on their velocity, amplitude, and frequency of occurrence. [11][12][13][14][15] The turbulence-driven transport results in broad plasma profiles in the SOL and enhanced levels of plasma--wall interactions that may be an issue for the next generation plasma confinement experiments and future fusion power reactors.…”

Section: Introductionmentioning

confidence: 99%

Stochastic modelling of intermittent fluctuations in the scrape-off layer: Correlations, distributions, level crossings, and moment estimation

et al. 2016

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A stochastic model is presented for intermittent fluctuations in the scrape-off layer of magnetically confined plasmas. The fluctuations in the plasma density are modeled by a super-position of uncorrelated pulses with fixed shape and duration, describing radial motion of blob-like structures. In the case of an exponential pulse shape and exponentially distributed pulse amplitudes, predictions are given for the lowest order moments, probability density function, auto-correlation function, level crossings, and average times for periods spent above and below a given threshold level. Also, the mean squared errors on estimators of sample mean and variance for realizations of the process by finite time series are obtained. These results are discussed in the context of single-point measurements of fluctuations in the scrape-off layer, broad density profiles, and implications for plasma--wall interactions due to the transient transport events in fusion grade plasmas. The results may also have wide applications for modelling fluctuations in other magnetized plasmas such as basic laboratory experiments and ionospheric irregularities. Published by AIP Publishing.

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Section: Introductionmentioning

confidence: 99%

Stochastic modelling of intermittent fluctuations in the scrape-off layer: Correlations, distributions, level crossings, and moment estimation

et al. 2016

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“…The scrape-off layer in a tokamak fusion plasma is replete with incoherent and coherent fluctuations -the latter being intermittent and in the form of blobs and filaments [1][2][3][4][5][6][7][8][9]. The edge plasma plays an important role in the transport of energy and particles to the divertor region and the plasma facing components, as well as in the fusion performance of the core plasma.…”

Section: Introductionmentioning

confidence: 99%

Scattering of radio frequency waves by cylindrical density filaments in tokamak plasmas

Ram

Hizanidis

2016

Physics of Plasmas

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In tokamak fusion plasmas, coherent fluctuations in the form of blobs or filaments are routinely observed in the scrape-off layer. Radio frequency (RF) electromagnetic waves, excited by antenna structures placed near the wall of a tokamak, have to propagate through the scrape-off layer before reaching the core of the plasma. While the effect of fluctuations on the properties of RF waves has not been quantified experimentally, it is of interest to carry out a theoretical study to determine if fluctuations can affect the propagation characteristics of RF waves. Usually, the difference between the plasma density inside the filament and the background plasma density is sizable; the ratio of the density difference to the background density being of order one. Generally, this precludes the use of geometrical optics in determining the effect of fluctuations since the relevant ratio has to be much less than one; typically, of the order of 10% or less. In this paper, a full-wave, analytical model is developed for the scattering of a RF plane wave by a cylindrical plasma filament. It is assumed that the plasma inside and outside the filament is cold and uniform, and that the major axis of the filament is aligned along the toroidal magnetic field. The ratio of the density inside the filament to the density of the background plasma is not restricted. The theoretical framework applies to the scattering of any cold plasma wave. In order to satisfy the boundary conditions at the interface between the filament and the background plasma, the electromagnetic fields inside and outside the filament need to have the same k ∥ , the wave vector parallel to the ambient magnetic field, as the incident plane wave. Consequently, in contrast to the scattering of a RF wave by a spherical blob [A. K. Ram, K. Hizanidis, and Y. Kominis, Phys. Plasmas 20, 056110-1-056110-10 (2013)], the scattering by a field-aligned filament does not broaden the k ∥ spectrum. However, the filament induces side-scattering leading to surface waves, and can also couple some power to the cold plasma wave different from the incident wave. The changes induced by a filament in the propagation of electron cyclotron waves and lower hybrid waves are illustrated by numerical results displaying the properties of the Poynting vector. The Poynting flux in the wake of the filament, and directed towards the core of the plasma, develops a spatial structure due to diffraction and shadowing. Thus, the fluctuations affect the uniformity of power flow into the plasma.

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“…In NSTX device the GPI consists of a double array of photomultiplier tubes that observes the radial-poloidal plane, i.e., the plane perpendicular to the magnetic field at the edge of a tokamak device (see references [19,20]). The signals are sampled at 0.5 Msamples/s.…”

Section: The Gpi Diagnosticsmentioning

confidence: 99%

On the statistics of edge fluctuations: comparative study between various fusion devices

Sattin

Agostini

Scarin

et al. 2009

Plasma Phys. Control. Fusion

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In this paper we present a statistical study of edge fluctuations taken with the Gas Puffing Imaging (GPI) diagnostics. We carry out a comparison of GPI signal from an extensive database including four devices (two Tokamaks and two Reversed Field Pinches). The data are analyzed in terms of their statistical moments Skewness and Kurtosis, as done in [B. Labit, et al, Phys. Rev. Lett. 98, 255002 (2007)]. The data align along parabolic curves, although different from machine to machine, with some spread around the best-fitting curve. A discussion about the meaning of the parabolic trend as well as the departure of real data from it is provided. A phenomenological model is finally provided, attempting to accomodate experimental evidence.

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Structure and motion of edge turbulence in the National Spherical Torus Experiment and Alcator C-Mod

Cited by 69 publications

References 30 publications

Stochastic modelling of intermittent fluctuations in the scrape-off layer: Correlations, distributions, level crossings, and moment estimation

Stochastic modelling of intermittent fluctuations in the scrape-off layer: Correlations, distributions, level crossings, and moment estimation

Scattering of radio frequency waves by cylindrical density filaments in tokamak plasmas

On the statistics of edge fluctuations: comparative study between various fusion devices

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