Beyond paradigm: Turbulence, transport, and the origin of the radial electric field in low to high confinement mode transitions in the DIII-D tokamak

Moyer, R. A.; Burrell, K.H.; Carlstrom, T. N.; Coda, S.; Conn, R.W.; Doyle, E. J.; Gohil, P.; Groebner, R. J.; Kim, J.; Lehmer, R.; Peebles, W. A.; Porkoláb, M.; Rettig, C. L.; Rhodes, T. L.; Seraydarian, R.; Stockdale, R. E.; Thomas, D.M.; Tynan, G. R.; Watkins, J.G.

doi:10.1063/1.871263

Cited by 263 publications

(275 citation statements)

References 42 publications

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“…The results strongly suggest that the intermittency is part of the turbulence. It can therefore be stated that the intermittency, and its response to sheared electric fields that decorrelate turbulent transport resulting in reduced transport and enhanced confinement conditions, has been indirectly characterized extensively in many devices such as CCT, 30,31 PBX-M, 32,33 DIII-D, 34 TEXT, 35,36 and TEXTOR. 37,38 Density profiles from Thomson scattering in the SOL, normalized to the value at the LCFS, are shown for L-and H-mode discharges in Fig.…”

Section: Results: L-h Mode Comparisonmentioning

confidence: 99%

Transport by intermittent convection in the boundary of the DIII-D tokamak

et al. 2001

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Intermittent plasma objects ͑IPOs͒ featuring higher pressure than the surrounding plasma, and responsible for ϳ50% of the EϫB T radial transport, are observed in the scrape off layer ͑SOL͒ and edge of the DIII-D tokamak ͓J. Watkins et al., Rev. Sci. Instrum. 63, 4728 ͑1992͔͒. Conditional averaging reveals that the IPOs, produced at a rate of ϳ3ϫ10 3 s Ϫ1 , are positively charged and also polarized, featuring poloidal electric fields of up to 4000 V/m. The IPOs move poloidally at speeds of up to 5000 m/s and radially with EϫB T /B 2 velocities of ϳ2600 m/s near the last closed flux surface ͑LCFS͒, and ϳ330 m/s near the wall. The IPOs slow down as they shrink in radial size from 4 cm at the LCFS to 0.5 cm near the wall. The IPOs appear in the SOL of both L and H mode discharges and are responsible for nearly 50% of the SOL radial EϫB transport at all radii; however, they are highly reduced in absolute amplitude in H-mode conditions.

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Section: Results: L-h Mode Comparisonmentioning

confidence: 99%

Transport by intermittent convection in the boundary of the DIII-D tokamak

et al. 2001

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“…Also evident is a sharp reduction in the fluctuations near 2.55 sec when the plasma undergoes a transition from a low-confinement mode (L-mode) to a high-confinement mode (H-mode). While the LH transition is primarily associated with the rapid development of a strong radial electric field shear layer and fluctuation suppression near the plasma pedestal (r/a > 0.9) [21], it is clear that fluctuations in this deeper core region are also affected and suppressed on a short time scale.…”

Section: Measured Turbulence Characteristicsmentioning

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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“…In this section, several aspects of the terminology and experimental technique are reviewed in order to facilitate commUncation. Techniques for studying the formation of E, and its role in H-mode physics have been recently discussed ( Burrell et al 1994a, Moyer et al 1995 and will not be repeated here.…”

Section: Terminology and Techniquementioning

confidence: 99%

Transition physics and scaling overview

Carlstrom

1996

Plasma Phys. Control. Fusion

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This paper presents an overview of recent experimental progress towards understanding H-mode transition physics and scaling. Terminology and techniques for studying H-mode are reviewed and discussed. The model of shear E × B flow stabilization of edge fluctuations at the L-H transition is gaining wide acceptance and is further supported by observations of edge rotation on a number of new devices. Observations of poloidal asymmetries of edge fluctuations and dephasing of density and potential fluctuations after the transition pose interesting challenges for understanding H-mode physics. Dedicated scans to determine the scaling of the power threshold have now been performed on many machines. A clear B t dependence is universally observed but dependence on the line averaged density is complicated. Other dependences are also reported. Studies of the effect of neutrals and error fields on the power threshold are under investigation. The ITER threshold database has matured and offers guidance to the power threshold scaling issues relevant to next-step devices.

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Beyond paradigm: Turbulence, transport, and the origin of the radial electric field in low to high confinement mode transitions in the DIII-D tokamak

Cited by 263 publications

References 42 publications

Transport by intermittent convection in the boundary of the DIII-D tokamak

Transport by intermittent convection in the boundary of the DIII-D tokamak

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

Transition physics and scaling overview

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