Study of edge turbulence in dimensionally similar laboratory plasmas

Stroth, U.; Greiner, Franko; Lechte, C.; Mahdizadeh, N.; Rahbarnia, K.; Ramisch, M.

doi:10.1063/1.1688789

Cited by 77 publications

(103 citation statements)

References 34 publications

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“…1 (top). The coil system corresponds to an l = 1, m = 6 torsatron and has a major plasma radius of R 0 = 0.6 m and a minor plasma radius of about a = 0.1 m. TJ-K is a low-temperature plasma experiment with cold ions [43], and with plasma parameters dimensionally similar to the edge of larger fusion experiments [44]. Due to the accessibility for Langmuir probes in the whole confinement region, it is an ideal test bed for turbulence investigations [34].…”

Section: Methodsmentioning

confidence: 99%

Spatial structure of drift-wave turbulence and transport in a stellarator

Birkenmeier¹,

Ramisch²,

Fuchert³

et al. 2012

Plasma Phys. Control. Fusion

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Abstract. The three-dimensional structure of drift-wave turbulence and turbulent transport is investigated in plasmas of the stellarator experiment TJ-K. By means of two poloidal Langmuir probe arrays placed at different toroidal positions, density and potential fluctuations are recorded simultaneously at 128 positions on a single flux surface. From this data, the spatial drift-wave turbulence pattern including perpendicular and parallel structure sizes are obtained using a cross-correlation technique. A comparison with the magnetic field structure indicates an initially perfect alignment of turbulent structures with magnetic field lines. Passing over regions with different field line pitches according to the local variation of the rotational transform, however, results in a measured displacement of turbulent structures with respect to the field lines during their radial propagation. A reduction of the perpendicular correlation lengths in regions of high absolute values of local magnetic shear is found. Prominent and poloidally narrow turbulent transport maxima are measured at different toroidal positions. They are connected by the magnetic field lines and located in regions of negative normal curvature. The poloidal propagation pattern of turbulent structures and the exact position of the transport maximum depend on the magnetic field direction.

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Section: Methodsmentioning

confidence: 99%

Spatial structure of drift-wave turbulence and transport in a stellarator

Birkenmeier¹,

Ramisch²,

Fuchert³

et al. 2012

Plasma Phys. Control. Fusion

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“…Drift waves preferentially propagate in the poloidal direction and not in the radial one across the shear layer as interchange modes do. In this presentation, experimental data which in the present detail can only be obtained in a low temperature plasma device as the one in the TJ-K stellerator [25], and gyrofluid simulations carried out with the GEMR code [26] are studied to develop a drift-wave based model for blob ejection consistent with the recent observations in the high temperature plasmas in ASDEX Upgrade, Alcator C-Mod and TJ-II [20][21][22].…”

Section: Introductionmentioning

confidence: 99%

Turbulent transport across shear layers in magnetically confined plasmas

et al. 2014

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Shear layers modify the turbulence in diverse ways and do not only suppress it. A spatialtemporal investigation of gyrofluid simulations in comparison with experiments allows to identify further details of the transport process across shear layers. Blobs in and outside a shear layer merge, thereby exchange particles and heat and subsequently break up. Via this mechanism particles and heat are transported radially across shear layers. Turbulence spreading is the immanent mechanism behind this process.

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“…[1][2][3][4]), but the detailed spatiotemporal structure and the interactions between fluctuations in turbulence have not been well understood. The electrostatic probe array can directly determine the turbulence structure, and multiple probe arrays [5,6] have been used in linear and torus devices. However, conventional arrays are fixed in space and cannot cover a wide measuring region.…”

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confidence: 99%

A Study on Low-Frequency Fluctuations Using New Azimuthal Probe Array in High-Density Helicon Linear Plasma

Terasaka

Shinohara

Nagashima

et al. 2007

Plasma and Fusion Research

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In a high-density plasma produced by helicon waves in a linear device, a change from the coherent to broadband density fluctuations was observed on increasing the magnetic field. The coherent mode exhibited the drift wave features, and a steady oscillation state was observed. When the magnetic field was increased, the fluctuation level increased, and the higher azimuthal Fourier components were excited. When the spectrum became broad at the higher magnetic field, the behavior of the azimuthal structure became complex and changed rapidly with time. The analysis performed using the movable probe array (48ch.-probe) decomposed the short-lived structure into poloidal mode-frequency space and indicated mode-mode coupling in the broad-band spectrum. In fusion plasmas, turbulence, particularly the drift wave turbulence, has been investigated actively. Recent works indicate that the mutual interaction between fluctuations, which have different temporal and spatial scales, plays an important role in turbulence dynamics. Thus, many studies have been conducted with torus and linear devices (e.g. [1][2][3][4]), but the detailed spatiotemporal structure and the interactions between fluctuations in turbulence have not been well understood. The electrostatic probe array can directly determine the turbulence structure, and multiple probe arrays [5,6] have been used in linear and torus devices. However, conventional arrays are fixed in space and cannot cover a wide measuring region. We have recently developed a new probe array consisting of 48 probes extended in the poloidal direction. Since this array is movable in the radial direction, it can measure plasma parameters in a wide radial-poloidal region, and thus, the poloidal mode-frequency space spectra, S (m, f ), can be analyzed. In this Rapid Communication, we report the first result from the proposed 48ch.-probe array.The 48ch.-probe has 16 modules using an individual 1.5 inch port. In addition, each module has three tungsten tips (the diameter and length are 0.8 mm and 4.0 mm, respectively), with the separation of 5.2 mm between two tips in the poloidal direction. In this experiment, all movable modules were set at r = 40 mm (hence 5.2 mm apart between all adjacent tips) and 1625 mm axially away from author's e-mail: tera-225@aees.kyushu-u.ac.jp the end of a helicon source tube. Drift wave measurements with the new probe array were performed in Large Mirror Device-Upgrade (LMD-U), which is a modification of the previous device [7]. The LMD-U consists of a cylindrical vacuum vessel, which is 3740 mm long and has a 445 mm inner diameter. The high-density helicon plasma is produced using a double-loop antenna with a width of 40 mm and axial central distance of 100 mm. The antenna is wound around a quartz tube, which is 400 mm long and has a 95 mm inner diameter. A magnetic field of up to 1500 G is generated by the coils around the vacuum vessel. In this experiment, argon gas was used with a pressure of 2 mTorr, and the RF power (frequency) was 3 kW (7 MHz). The typical electr...

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Study of edge turbulence in dimensionally similar laboratory plasmas

Cited by 77 publications

References 34 publications

Spatial structure of drift-wave turbulence and transport in a stellarator

Spatial structure of drift-wave turbulence and transport in a stellarator

Turbulent transport across shear layers in magnetically confined plasmas

A Study on Low-Frequency Fluctuations Using New Azimuthal Probe Array in High-Density Helicon Linear Plasma

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