Modifications in turbulence and edge electric fields at the L–H transition in the DIII-D tokamak

Doyle, E. J.; Groebner, R. J.; Burrell, K.H.; Gohil, P.; Lehecka, T.; Luhmann, N. C.; Matsumoto, Hiroshi; Osborne, T. H.; Peebles, W. A.; Philipona, Rolf

doi:10.1063/1.859597

Cited by 233 publications

(149 citation statements)

References 29 publications

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“…5, show core fluctuations with the radial correlation length of 3 to 4 cm. The reflectometry measurements of Doyle et al (1991) show evidence for the bifurcation in the fluctuation levels associated with a change in the confinement properties.…”

Section: J Long-wavelength Electron Drift Wavesmentioning

confidence: 99%

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Drift waves and transport

1999

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Drift waves occur universally in magnetized plasmas producing the dominant mechanism for the transport of particles, energy and momentum across magnetic field lines. A wealth of information obtained from quasistationary laboratory experiments for plasma confinement is reviewed for drift waves driven unstable by density gradients, temperature gradients and trapped particle effects. The modern understanding of Bohm transport and the role of sheared flows and magnetic shear in reducing the transport to the gyro-Bohm rate are explained and illustrated with large scale computer simulations. The types of mixed wave and vortex turbulence spontaneously generated in nonuniform plasmas are derived with reduced magnetized fluid descriptions. The types of theoretical descriptions reviewed include weak turbulence theory, Kolmogorov anisotropic spectral indices, and the mixing length. A number of standard turbulent diffusivity formulas are given for the various space-time scales of the drift-wave turbulent mixing. [S0034-6861(99)00803-X] CONTENTS

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Section: J Long-wavelength Electron Drift Wavesmentioning

confidence: 99%

“…The fluctuation measurement at wave numbers k Ќ Շ1 cm Ϫ1 require the techniques of reflectometry (Doyle et al, 1991;Mazzucato and Nazikian, 1993) and the indirect method of beam emission spectroscopy as in the Durst et al (1993) experiment.…”

Section: Drift-wave Diffusivities and The Ion Inertial Scale Lengthmentioning

confidence: 99%

Drift waves and transport

1999

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“…Microwave measurements have been used to determine many important properties of fusion plasmas, such as density 1 , magnetic field strength 2 , fluctuations 3 , and flows 4 .…”

Section: Introductionmentioning

confidence: 99%

Assessment of microwave power flow for reflectometry measurements in tokamak plasmas

Gourdain¹,

Peebles²

2008

Plasma Phys. Control. Fusion

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Microwave diagnostics, such as reflectometry and electron cyclotron emission, are widely employed in tokamak fusion plasmas, and are also particularly well suited to the burning plasma environment expected in the upcoming ITER device. In existing fusion plasmas, reflectometry has been used to measure electron density profile, density fluctuations, turbulent flow and internal magnetic field strength. The measurement of electron density profile via reflectometry is a particularly high priority in ITER, and so an assessment of electromagnetic wave propagation is important in estimating measurement capability. In ITER, the ratio of plasma size to the required microwave signal wavelength is significantly larger than in current fusion experiments ensuring a more realistic analysis of reflectometry via ray-tracing techniques. The analytical and numerical studies presented in this paper highlight the fact that the group velocity (or power flow) is strongly dependent on the direction of wave propagation relative to the magnetic field. It is shown that this dependence strongly modifies power flow near the cut-off layer in a manner that embeds the local magnetic field direction in the 'footprint' of the returned power at the launch antenna. It will be shown that this can potentially be utilized to determine the magnetic field pitch angle at the cut-off location. The resultant beam drift and distortion due to the magnetic field also have consequences on the design of reflectometry systems for large, high-field fusion experiments such as ITER.

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“…Broadband precursors to type I ELMs have also been documented [12]. Less attention has been devoted to fluctuations occurring during the ELM itself, partly because of the short duration of the event.…”

Section: Introductionmentioning

confidence: 99%

“…Coherent or semi-coherent precursor fluctuations have often been seen in the 20-100 kHz spectral region, from 1 up to 20 ms before an ELM, both in density (by reflectometry [12]) and in magnetic field [10,13,14]. Broadband precursors to type I ELMs have also been documented [12].…”

Section: Introductionmentioning

confidence: 99%

Characterization of density fluctuations during ELMs in the DIII-D tokamak

2001

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Abstract. Bursts of turbulence associated with ELMs have been studied systematically in DIII-D with a multichannel phase contrast imaging (PCI) diagnostic, which is sensitive to the long poloidal wavelength components of the density fluctuations in the outer edge of the tokamak. A comparison of the temporal dynamics of the turbulence with the signature Dα signal from the divertor has revealed systematic differences between type I and type III ELMs: even though precursor fluctuations are sometimes seen before type I ELMs, the PCI signal level remains high until the peak in the Dα signal; by contrast, in type III ELMs the fluctuation burst precedes the Dα peak by 0.4-0.6 ms. Type I ELMs can generate 'echoes', i.e. secondary bursts, in the scrape-off layer. Coherent modes are observed during type III ELMs only. The radial and temporal correlation structures and the spectral properties of the turbulence during the transient ELM phase have been reconstructed by averaging over multiple ELMs, in order to improve the statistical accuracy. ELM turbulence is found to share many properties with L mode turbulence, including the main qualitative features of radial wavenumber and frequency spectra and radial dispersion relations. However, features unique to ELM turbulence are also identified.

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Modifications in turbulence and edge electric fields at the L–H transition in the DIII-D tokamak

Cited by 233 publications

References 29 publications

Drift waves and transport

Drift waves and transport

Assessment of microwave power flow for reflectometry measurements in tokamak plasmas

Characterization of density fluctuations during ELMs in the DIII-D tokamak

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