Investigation of turbulence rotation and radial electric field in the island divertor and plasma edge at W7-X

Krämer‐Flecken, A.; Han, Xiang; Windisch, T.; Cosfeld, J.; Drews, P.; Fuchert, G.; Geiger, J.; Grulke, O.; Killer, C.; Knieps, A.; Liang, Y.; Liu, Shaocheng; Rack, M.

doi:10.1088/1361-6587/ab0624

Cited by 28 publications

(43 citation statements)

References 18 publications

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“…It is interesting to note that particularly in the standard configuration with I cc = 0 differences in the SOL profiles across the magnetic islands have been reported. Observations include nonmonotonic T e profiles [15,20,25,26], a poloidal plasma rotation around the islands due to an 'island radial electric field' [20,27], and a still unexplained fast correlation of plasma fluctuations between inboard and outboard side of an island [13]. The large scatter in the I cc = 0 data in figure 5 further emphasizes the additional complexity that magnetic islands can entail.…”

Section: Turbulent Transport Vs Local Gradientsmentioning

confidence: 93%

Turbulent transport in the scrape-off layer of Wendelstein 7-X

2021

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Turbulent transport is widely considered to be the main driver for cross-field transport in the scrape-off layer (SOL) of toroidal magnetized plasmas. Here, reciprocating Langmuir probes are employed to measure both the plasma profiles and the turbulent particle transport in the SOL of the Wendelstein 7-X stellarator. The relation between turbulent radial particle flux Γ r and the local pressure gradient is often approximately linear across the entire SOL width, indicating that radial turbulence spreading is absent. This observation holds across a wide range of magnetic configurations and different plasma heating and density scenarios. The magnitude of the turbulent transport for a given gradient reveals a dependence on the magnetic configuration and the position in the SOL, which we relate to the cross-spectral characteristics of multi-tip floating potential measurements. Magnetic islands can add further complexity due to non-monotonic SOL profiles and the breaking of the transport-gradient relation. Finally, anomalous diffusion coefficients are determined from the probe measurements.

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Section: Turbulent Transport Vs Local Gradientsmentioning

confidence: 93%

Turbulent transport in the scrape-off layer of Wendelstein 7-X

2021

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“…At the island position the connection length increases and a small well defined region is created with good confinement. In this region the sign of v ⊥ changes again [16]. Three different scans are analysed at different I p values to study the effect of the plasma current on the island.…”

Section: Observationsmentioning

confidence: 99%

Investigation of turbulence rotation in the SOL and plasma edge of W7-X for different magnetic configurations

Krämer‐Flecken¹,

Han

Otte

et al. 2020

Plasma Sci. Technol.

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The W7-X stellarator is optimized for neoclassical transport and turbulent transport plays an important role. It is equipped with a inertial cooled Graphite divertor which intersects, depending on the magnetic configuration the island chain at the plasma edge. Additional control coils and the plasma current modify the iota profile at the plasma edge and shift the position of the island chain. To monitor the effects on the poloidal propagation velocity in the scrape off layer (SOL) and the plasma edge an O-mode Poloidal Correlation Reflectometer is used which simultaneously monitors the propagation of low k-turbulence. Operating in the density range 0.6 × 10 19 m −3 to 2 × 10 19 m −3 it covers a large part of the SOL and the plasma edge and allows in low to medium density discharges to determine experimentally the last closed flux surface (LCFS) and the associated shear layer.In this paper it is shown that the propagation in the shear layer and its vicinity is determined best, when based on an elliptical model. Different magnetic configurations having an edge iota of ι = 1 and ι = 0.81 are investigated. Also the effects of the plasma current and additional control coils on the edge magnetic topology are studied.

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“…The perpendicular velocity (v ⊥ ) and radial electron field (E r ) profiles in the vicinity of magnetic islands have been measured successfully via PCR [26] and compared well with the combined probe [27].…”

Section: Experimental Setup On W7-xmentioning

confidence: 99%

Experimental characterization of a quasi-coherent turbulent structure in the edge plasma in Wendelstein 7-X

et al. 2019

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A quasi-coherent mode (QCM) near the plasma edge is characterized experimentally by measuring the density fluctuation via a poloidal correlation reflectometer (PCR) in Wendelstein 7-X. This QCM frequency descends from 25 kHz near the separatrix to 10 kHz as the cutoff position penetrates toward the core. A similar mode structure is also observed in the spectra of ECE edge channels and Mirnov coil signals, which shows a clear correlation with respect to the PCR measurement. The mode evaluation yields a range for the poloidal mode number of 8 ≤ m ≤ 25, and for the normalized mode scale k ⊥ ρ s ≤ 0.1, which suggest a drift type instability. The QCM structure appears in the standard and narrow-mirror configurations (both with the rotational transform ι = 5/5 in the boundary), but is absent in the high-ι configuration (boundary ι = 5/4). The impact of plasma parameters on the QCM is discussed. It is observed that the QCM frequency and amplitude can be affected by the edge magnetic topology and plasma parameters. The f mode shifts upward during the negative and non-stellarator-symmetric control coil current scans, which may be attributed to the effect of the E × B shear, E r , and n e in the plasma edge region.

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Investigation of turbulence rotation and radial electric field in the island divertor and plasma edge at W7-X

Cited by 28 publications

References 18 publications

Turbulent transport in the scrape-off layer of Wendelstein 7-X

Turbulent transport in the scrape-off layer of Wendelstein 7-X

Investigation of turbulence rotation in the SOL and plasma edge of W7-X for different magnetic configurations

Experimental characterization of a quasi-coherent turbulent structure in the edge plasma in Wendelstein 7-X

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