Study of intermittent small-scale turbulence in Wendelstein 7-AS plasmas during controlled confinement transitions

Basse, N.; Zoletnik, S.; Michelsen, Poul; Team, W As

doi:10.1063/1.1818142

Cited by 6 publications

(4 citation statements)

References 27 publications

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“…A close relation between the rationals, confinement, and transport was also found in Wendelstein 7-AS, where the value of the rotational transform in the edge was varied both by current drive and a configuration scan [28,29], these two methods being equivalent. The modes m/n = 3/9 and 3/10 were located inside the plasma and, depending on their phases and positions, a transition from a bad to a good confinement regime, accompanied by a decrease in the of fluctuations, was observed.…”

Section: The Role Of Low Order Rationalssupporting

confidence: 62%

Influence of magnetic topology on transport and stability in stellarators

Castejón¹,

Fujisawa

Ida

et al. 2005

Plasma Phys. Control. Fusion

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The influence of the magnetic topology on transport and stability has been investigated in four stellarators: an almost shearless medium size flexible heliac (TJ-II), a medium size and a large heliotron (CHS and LHD) with shear, and a quasihelically symmetric device (HSX) with moderate shear. All of these have variable rotational transform profiles and magnetic ripples. Using these capabilities, bifurcated states can appear and plasma can jump from one to another with subsequent changes in the transport properties. Low rational values of ι/2π can create transport barriers in LHD and TJ-II when they are located close to the plasma core or at the edge. The key ingredient for transport barriers is a positive and sheared electric field. Internal transport barriers also appear in CHS, but the role of rationals is not clear yet in this device. The time evolution of the electric field shows the onset of a bifurcation triggered either by the rational or by the presence of the ion and electron roots. The electric potential inside ITBs follows the ECE-temperature profile in a fast time scale. The plasma stability properties and its effect on the viscosity are also studied in the HSX, and the influence of the dynamics of rational surface is studied in the LHD and TJ-II stellarators.

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Section: The Role Of Low Order Rationalssupporting

confidence: 62%

Influence of magnetic topology on transport and stability in stellarators

Castejón¹,

Fujisawa

Ida

et al. 2005

Plasma Phys. Control. Fusion

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“…232 Other types of turbulence diagnostics have seen limited use for the study of blobs. Electromagnetic diagnostics such as microwave reflectometry, 1 microwave scattering, 183 phase contrast imaging 181 generally do not have enough 2D spatial resolution to detect a localized blob. A heavy ion beam probe diagnostic has been used to identify radially elongated streamerlike structures in JIPP T-IIU tokamak.…”

Section: B Diagnosticsmentioning

confidence: 99%

Convective transport by intermittent blob-filaments: Comparison of theory and experiment

2011

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A blob-filament (or simply “blob”) is a magnetic-field-aligned plasma structure which is considerably denser than the surrounding background plasma and highly localized in the directions perpendicular to the equilibrium magnetic field B. In experiments and simulations, these intermittent filaments are often formed near the boundary between open and closed field lines, and seem to arise in theory from the saturation process for the dominant edge instabilities and turbulence. Blobs become charge-polarized under the action of an external force which causes unequal drifts on ions and electrons; the resulting polarization-induced E × B drift moves the blobs radially outwards across the scrape-off-layer (SOL). Since confined plasmas generally are subject to radial or outwards expansion forces (e.g., curvature and ∇B forces in toroidal plasmas), blob transport is a general phenomenon occurring in nearly all plasmas. This paper reviews the relationship between the experimental and theoretical results on blob formation, dynamics and transport and assesses the degree to which blob theory and simulations can be compared and validated against experiments.

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“…r The theory is reviewed from a practical point of view; the work done is in support of measurements of density fluctuations in the Wendelstein 7-AS (W7-AS) stellarator [1]. Here, we used a CO 2 laser having a wavelength of 10.59 m to make smallangle measurements [2][3][4][5][6][7][8].…”

Section: A Motivationmentioning

confidence: 99%

Small-angle Scattering Theory Revisited: Photocurrent and Spatial Localization

Basse

Zoletnik

Michelsen³

2005

Phys. Scr.

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In this paper theory on collective scattering measurements of electron density fluctuations in fusion plasmas is revisited. We present the first full derivation of the expression for the photocurrent beginning at the basic scattering concepts. Thereafter we derive detailed expressions for the auto- and crosspower spectra obtained from measurements. These are discussed and simple simulations made to elucidate the physical meaning of the findings. In this context, the known methods of obtaining spatial localization are discussed and appraised. Where actual numbers are applied, we utilize quantities from two collective scattering instruments The ALTAIR diagnostic on the Tore Supra tokamak [A Truc et al, "ALTAIR An infrared laser scattering diagnostic on the Tore Supra tokamak", Rev. Sci. Instrum. 63 3716–3724 (1992)] and the LOTUS diagnostic on the Wendelstein 7-AS stellarator [M Saffman et al, "CO2 laser based two-volume collective scattering instrument for spatially localized turbulence measurements", Rev. Sci. Instrum. 72 2579–2592 (2001)].

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Study of intermittent small-scale turbulence in Wendelstein 7-AS plasmas during controlled confinement transitions

Cited by 6 publications

References 27 publications

Influence of magnetic topology on transport and stability in stellarators

Influence of magnetic topology on transport and stability in stellarators

Convective transport by intermittent blob-filaments: Comparison of theory and experiment

Small-angle Scattering Theory Revisited: Photocurrent and Spatial Localization

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