Structure of edge-plasma turbulence in the Caltech tokamak

Zweben, S. J.; Gould, R. W.

doi:10.1088/0029-5515/25/2/005

Cited by 149 publications

(141 citation statements)

References 20 publications

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“…Despite the significant development of fluctuation diagnostics, there are remarkably few that can measure fluctuations in 2D. Such diagnostics have included probe arrays [4], gas puff imaging systems [5][6][7] and an earlier generation beam emis-sion spectroscopy system [8][9][10]. These diagnostics were limited to the edge, separatrix, and scrape off regions or cold plasmas due to the various diagnostic limitations.…”

Section: Introductionmentioning

confidence: 99%

Plasma Turbulence Imaging via Beam Emission Spectroscopy in the Core of the DIII-D Tokamak

McKee

Fonck

Gupta

et al. 2007

Plasma and Fusion Research

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Beam Emission Spectroscopy (BES), a high-sensitivity, good spatial resolution imaging diagnostic system, has been deployed and recently upgraded and expanded at the DIII-D tokamak to better understand density fluctuations arising from plasma turbulence. The currently deployed system images density fluctuations over an approximately 5 × 7 cm region at the plasma mid-plane (radially scannable over 0.2 < r/a ≤ 1) with a 5 × 6 (radial × poloidal) grid of rectangular detection channels, with one microsecond time resolution. BES observes collisionally-induced, Doppler-shifted D α fluorescence (λ = 652-655 nm) of injected deuterium neutral beam atoms. The diagnostic wavenumber sensitivity is approximately k ⊥ < 2.5 cm −1 , allowing measurement of longwavelength (k ⊥ ρ I < 1) density fluctuations. The recent upgrade includes expanded fiber optics bundles, customdesigned high-transmission, sharp-edge interference filters, ultra fast collection optics, and enlarged photodiode detectors that together provide nearly an order of magnitude increase in sensitivity relative to an earlier generation BES system. The high sensitivity allows visualization of turbulence at normalized density fluctuation amplitudes ofn/n < 1%, typical of fluctuation levels in the core region. The imaging array allows for sampling over 2-3 turbulent eddy scale lengths, which captures the essential dynamics of eddy evolution, interaction and shearing.

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Section: Introductionmentioning

confidence: 99%

Plasma Turbulence Imaging via Beam Emission Spectroscopy in the Core of the DIII-D Tokamak

McKee

Fonck

Gupta

et al. 2007

Plasma and Fusion Research

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“…This paper will discuss the diagnostic system, examples of turbulence imaging measurements, and progress on development of new analysis techniques. We note that twodimensional turbulence images have been obtained in relatively cold plasmas using Langmuir probe arrays, 7 and a gas puff imaging system has been recently developed to image light emission from edge/scrape-off layer turbulence in C-MOD and NSPX. 8 …”

Section: Introductionmentioning

confidence: 99%

Turbulence imaging and applications using beam emission spectroscopy on DIII-D (invited)

McKee

Fenzi

Fonck

et al. 2003

Review of Scientific Instruments

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Two-dimensional measurements of density fluctuations are obtained in the radial and poloidal plane of the DIII-D tokamak with the Beam Emission Spectroscopy ͑BES͒ diagnostic system. The goals are to visualize the spatial structure and time evolution of turbulent eddies, as well as to obtain the 2D statistical properties of turbulence. The measurements are obtained with an array of localized BES spatial channels configured to image a midplane region of the plasma. 32 channels have been deployed, each with a spatial resolution of about 1 cm in the radial and poloidal directions, thus providing measurements of turbulence in the wave number range 0Ͻk Ќ р3 cm Ϫ1 . A 5 (radial) ϫ6 (poloidal) channel grid provides time-resolved images near the outer midplane at the sampling frequency of 1 MHz, thus providing a modest spatial resolution, high throughput, high time resolution turbulence imaging system. The images and resulting movies have broad application to a wide variety of fundamental turbulence studies: imaging of the highly complex, nonlinear turbulent eddy interactions, measurement of the 2D correlation function, and S(k r ,k ) wave number spectra, and direct measurement of the equilibrium and time-dependent turbulence flow field. The time-dependent, two-dimensional turbulence velocity flow-field is obtained with time-delay-estimation techniques.

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“…22.) It was also found that the saturation amplitude and the associated quasilinear diffusion were greatly en- [11][12][13] which indicate that in the edge region, the fluctuation amplitude is rather insensitive to collisions whereas diffusion increases with density (i.e.. sensitive to collisions). We will elaborate on these points later.…”

Section: Introductionmentioning

confidence: 99%

Nonlinear evolution of drift instabilities in the presence of collisions

Federici

Lee

Tang

1987

The Physics of Fluids

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PPPL-2354 DE86 013642Nonlinear evolution of drift instabilities in the presence of electron-ion collisions in a shear-free slab has been studied by using gyrokinetic particle simulation tech niques as well as by solving, both numerically and analytically, model mode-coupling equations. The purpose of the investigation is to determine the mechanisms respon sible for the nonlinear saturation of the instability and for the ensuing steady-state transport. Such an insight is very valuable for understanding drift wave problems in more complicated geometries. The results indicate that the electron E x B convection is the dominant mechanism for saturation. It is also found that the saturation amplitude and the associated quasilinear diffusion are greatly enhanced over their collisionless values as a result of weak collisions. In the highly collisional (fluid) limit, there is an upper bound for saturation with e/T e ~ (<^i/tti)/(k±p,) 2 .The associated quasilinear diffusion, which increases with collisionality, takes the form of D q i ~ -yi/k±, where u>; and 7; are the linear frequency and growth rate, re spectively. In the steady state, the diffusion process becomes stochastic in nature.The relevant mechanisms here are related to the velocity-space nonlinearities and DISTRIBUTION OF THIS DOCUMENT IS UNLIMITED background fluctuations. The magnitude of the diffusion at this stage can be com parable to that of quasilinear diffision in the presance of collisions, and it remains finite even in the collisionless limit.

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Structure of edge-plasma turbulence in the Caltech tokamak

Cited by 149 publications

References 20 publications

Plasma Turbulence Imaging via Beam Emission Spectroscopy in the Core of the DIII-D Tokamak

Plasma Turbulence Imaging via Beam Emission Spectroscopy in the Core of the DIII-D Tokamak

Turbulence imaging and applications using beam emission spectroscopy on DIII-D (invited)

Nonlinear evolution of drift instabilities in the presence of collisions

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