The spatial structure of edge fluctuations in the Wendelstein 7-AS stellarator

Bleuel, J.; Endler, M.; Niedermeyer, H.; Schubert, M.; Thomsen, H.; Team, W As

doi:10.1088/1367-2630/4/1/338

Cited by 73 publications

(93 citation statements)

References 49 publications

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“…are in the range from 70 to 90% for density-density, density-potential and potential-potential correlations. They are somewhat smaller than results from larger experiments [6,35], which yielded correlations of more than 90% over a 10 m distance between probes. It has to be investigated, whether this is due to the strong local shear in TJ-K.…”

Section: Turbulence Measurements and Comparisonscontrasting

confidence: 62%

“…By means of correlation techniques, the spatial structure of the microfluctuations perpendicular and parallel to the magnetic field were measured in the scrape-off layer (SOL) of stellarators and tokamaks [5,6]. The results are consistent with predictions from electrostatic interchange turbulence.…”

Section: Introductionsupporting

confidence: 53%

“…All signals were correlated directly as well as by conditional averaging. These are methods which yield the average structure of the larger events [6,34]. The results from both methods are consistent.…”

Section: Turbulence Measurements and Comparisonsmentioning

confidence: 52%

“…From correlation experiments in linear devices [21] and in the fusion SOL [6] phases of typically π/2 are reported. Since this technique is sensitive to larger modes or events, the same ambiguity as discussed above might also exist.…”

Section: Summary and Discussionmentioning

confidence: 99%

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Comparison of turbulence measurements and simulations of the low-temperature plasma in the torsatron TJ-K

2002

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Abstract. A toroidal low-temperature plasma is used for comparative turbulence studies. Measurements are carried out with Langmuir probe arrays in the entire plasma cross section. The data are closely compared with drift-Alfvén turbulence simulations. Although the parameters in a low-temperature plasma are very different from those in fusion plasmas, the dimensionless parameters governing the drift-wave physics are comparable. Hence this study can also give insight into high-temperature plasma turbulence. In order to identify relevant characteristic signatures of different turbulence-driving mechanisms, simulations were carried out for a wide range of plasma parameters. The simulation results are compared with first measurements.

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Section: Turbulence Measurements and Comparisonscontrasting

confidence: 62%

Section: Introductionsupporting

confidence: 53%

Section: Turbulence Measurements and Comparisonsmentioning

confidence: 52%

Section: Summary and Discussionmentioning

confidence: 99%

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Comparison of turbulence measurements and simulations of the low-temperature plasma in the torsatron TJ-K

2002

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“…However, due to limited experimental access, such an approach to the 3D structure of turbulence has to our knowledge not been realized in a fusion device. Typical experimental setups are limited to two sampling points in the toroidal direction [4,5,8]. A more sophisticated approach has been realized in the TJ-K torsatron [10] and in a similar manner in WEGA.…”

Section: Introductionmentioning

confidence: 99%

The parallel dynamics of drift wave turbulence in the WEGA stellarator

Marsen¹,

Endler²,

Otte³

et al. 2009

Plasma Phys. Control. Fusion

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Abstract. The three-dimensional structure of turbulence in the edge (inside the last closed flux surface) of the WEGA stellarator is studied focussing on the parallel dynamics. WEGA as a small stellarator with moderate plasma parameters offers the opportunity to study turbulence with Langmuir probes providing high spatial and temporal resolution. Multiple probes with radial, poloidal and toroidal resolution are used to measure density fluctuations. Correlation analysis is used to reconstruct a 3D picture of turbulent structures. We find that these structures originate predominantly on the low field side and have a three-dimensional character with a finite averaged parallel wavenumber. The ratio between parallel and perpendicular wavenumber component is in the order of 10 −2 . The parallel dynamics are compared at magnetic inductions of 57 mT and 500 mT. At 500 mT, the parallel wavelength is in the order of the field line connection length 2πR/ῑ. A frequency resolved measure of k /k θ shows a constant ratio in this case. At 57 mT the observed k is much smaller than at 500 mT. However, the observed small average value is due to an averaging over positive and negative components pointing parallel and antiparallel to the magnetic field vector.

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Observation of Mode like Coherent Structures in Curved Magnetic Fields of a Simple Magnetized Torus

Greiner¹,

Block

Piel

2004

Contrib. Plasma Phys.

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The spatio-temporal dynamics of large-scale structures in curved magnetic field of simple magnetized torus (SMT) are presented. The experiments are performed in the SMT BLAAMANN and employ the techniques of conditional averaging (CA) and cross-correlation (CCF) of Langmuir probe data. By means of a detailed comparison of radio-frequency and thermionic discharges, it is shown that general features of the observed large-scale structures are independent of the discharge mechanism. Further, the observed large scale structures have a pronounced spatio-temporal periodicity, which suggests a description as mode-like. The conjectured relationship between the observed coherent structures and the inverse energy cascade is therefore questioned again.

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The spatial structure of edge fluctuations in the Wendelstein 7-AS stellarator

Cited by 73 publications

References 49 publications

Comparison of turbulence measurements and simulations of the low-temperature plasma in the torsatron TJ-K

Comparison of turbulence measurements and simulations of the low-temperature plasma in the torsatron TJ-K

The parallel dynamics of drift wave turbulence in the WEGA stellarator

Observation of Mode like Coherent Structures in Curved Magnetic Fields of a Simple Magnetized Torus

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