Edge flow measurements with Gundestrup probes

Gunn, J.; Boucher, C.; Devynck, P.; Ďuran, I.; Dyabilin, K. S.; Horáček, J.; Hron, M.; Ştöckel, J.; Oost, G. Van; Goubergen, H. van; Žáček, F.

doi:10.1063/1.1344560

Cited by 57 publications

(56 citation statements)

References 19 publications

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“…It should be noted that these estimates of E r and ω E×B do not take into account the electron temperature contribution to the plasma potential. Besides, all but the innermost pins in the 2D probe are shadowed by the insulating Boron Nitride probe body, which may introduce further (although smaller) corrections to the mean plasma potential caused by the density wake of the parallel ion flow past the probe [21]. However their observed modulations or relative changes are less sensitive to these corrections and are considered a good proxy of plasma potential modifications.…”

Section: Global Modulations Of Floating Potential Profile and Zf Dynamentioning

confidence: 99%

Dynamic transport regulation by zonal flow-like structures in the TJ-II stellarator

Alonso¹,

Hidalgo²,

Pedrosa³

et al. 2012

Nucl. Fusion

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Abstract. Floating potential structures that are correlated over a long distance are observed with a 2D probe array in the plasma edge of the TJ-II stellarator. We introduce a method based on the Singular Value Decomposition to extract the spatiotemporal structure of the global, fluctuating, zonal-flow-like floating potential from the combined measurements of a 2D probe array and a distant single probe. The amplitude of these global structures is seen to modulate not only the high k θ spectral power of the local turbulence, but also particle transport into the unconfined Scraped-Off Layer, as observed by H α monitors around the device. These observations provide the first direct evidence of the global modulation of transport by zonal flow-like structures. The ability to identify spontaneous and collective rotation events with flux surface symmetry opens up the possibility to perform unperturbative studies of the effective viscosity in stellarators and tokamaks.

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Section: Global Modulations Of Floating Potential Profile and Zf Dynamentioning

confidence: 99%

Dynamic transport regulation by zonal flow-like structures in the TJ-II stellarator

Alonso¹,

Hidalgo²,

Pedrosa³

et al. 2012

Nucl. Fusion

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“…Firstly, the E Â B drift velocity is calculated from the plasma potential profile measured by a swept Langmuir probe. Then, a Gundestrup (Mach) probe 16 with six faces is used to measure the flows directly in several bias voltages. Figure 3 shows the radial profiles of the flow velocity measured by both methods in helium plasma with 150 V bias on the annulus.…”

Section: Methodsmentioning

confidence: 99%

Sheared-flow induced confinement transition in a linear magnetized plasma

et al. 2012

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A magnetized plasma cylinder (12 cm in diameter) is induced by an annular shape obstacle at the Large Plasma Device [W. Gekelman, H. Pfister, Z. Lucky, J. Bamber, D. Leneman, and J. Maggs, Rev. Sci. Instrum. 62, 2875(1991]. Sheared azimuthal flow is driven at the edge of the plasma cylinder through edge biasing. Strong fluctuations of density and potential (dn=n $ ed/=kT e $ 0:5) are observed at the plasma edge, accompanied by a large density gradient (L n ¼ jr ln nj À1 $ 2 cm) and shearing rate (c $ 300 kHz). Edge turbulence and cross-field transport are modified by changing the bias voltage (V bias ) on the obstacle and the axial magnetic field (B z ) strength. In cases with low V bias and large B z , improved plasma confinement is observed, along with steeper edge density gradients. The radially sheared flow induced by E Â B drift dramatically changes the cross-phase between density and potential fluctuations, which causes the wave-induced particle flux to reverse its direction across the shear layer. In cases with higher bias voltage or smaller B z , large radial transport and rapid depletion of the central plasma density are observed. Two-dimensional cross-correlation measurement shows that a mode with azimuthal mode number m ¼ 1 and large radial correlation length dominates the outward transport in these cases. Linear analysis based on a two-fluid Braginskii model suggests that the fluctuations are driven by both density gradient (drift wave like) and flow shear (Kelvin-Helmholtz like) at the plasma edge.

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“…It is not so natural to make that approximation for the ions. However, it is known from other calculations [25,9] that the isothermal approximation gives results quite close to those that arise from more physically plausible approximations. In any case, the standard widely-accepted formulas are based upon isothermal-ion calculations.…”

Section: Discussionmentioning

confidence: 87%

“…A related, but more intuitive and probably more relevant correction comes from edges of plane facets. Most Mach probes have electrodes at or near their ends [12,9,13,24] The direction δ ll associated with the surfaces points forward, beyond the probe end, on one side and backward towards the probe stalk on the other, as illustrated in Fig 7. The surface for which it points backward collects essentially zero flux for a distance ≈ δ l from the end, because of the magnetic presheath displacement; then it collects the full flux from then on. The surface for which δ ll points forward collects full flux at its end.…”

Section: Probe Curvature and Finite Facet Sizementioning

confidence: 99%

See 1 more Smart Citation

Oblique ion collection in the drift approximation: How magnetized Mach probes really work

Hutchinson

2008

Physics of Plasmas

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The anisotropic fluid equations governing a frictionless obliquely-flowing plasma around an essentially arbitrarily shaped three-dimensional ion-absorbing object in a strong magnetic field are solved analytically in the quasi-neutral drift-approximation, neglecting parallel temperature gradients. The effects of transverse displacements traversing the magnetic presheath are also quantified. It is shown that the parallel collection flux density dependence upon external Mach-number is n ∞ c s exp[−1 − (M ∞ − M ⊥ cot θ)] where θ is the angle (in the plane of field and drift velocity) of the object-surface to the magnetic-field and M ∞ is the external parallel flow. The perpendicular drift, M ⊥ , appearing here consists of the external E ∧ B drift plus a weighted sum of the ion and electron diamagnetic drifts that depends upon the total angle of the surface to the magnetic field. It is that somewhat counter-intuitive combination that an oblique (transverse) Mach probe experiment measures.

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Edge flow measurements with Gundestrup probes

Cited by 57 publications

References 19 publications

Dynamic transport regulation by zonal flow-like structures in the TJ-II stellarator

Dynamic transport regulation by zonal flow-like structures in the TJ-II stellarator

Sheared-flow induced confinement transition in a linear magnetized plasma

Oblique ion collection in the drift approximation: How magnetized Mach probes really work

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