Digital signal processing techniques for plasma dispersion curve measurements

Elliott, J A

doi:10.1088/0022-3735/20/11/006

Cited by 10 publications

(16 citation statements)

References 14 publications

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“…This measurement methodology is similar to one obtained by Briggs [10] and applied to plasmas in [11]. Summarizing, the measurement of v ⊥ from time delay analyses using this method can be achieved when the following conditions are fulfilled:…”

Section: Time Delay Estimation In Tokamaksmentioning

confidence: 90%

Magnetic field pitch angle and perpendicular velocity measurements from multi-point time-delay estimation of poloidal correlation reflectometry

Prisiazhniuk

Krämer–Flecken

Happel

et al. 2017

Plasma Phys. Control. Fusion

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Abstract. In fusion machines turbulent eddies are expected to be aligned with the direction of the magnetic field lines and to propagate in the perpendicular direction. Time delay measurements of density fluctuations can be used for the calculation of magnetic field pitch angle α and perpendicular velocity v ⊥ profiles. The method is applied to poloidal correlation reflectometry installed at ASDEX Upgrade and TEXTOR, which measure density fluctuations from poloidally and toroidally separated antennas. Validation of the method is achieved by comparison of the perpendicular velocity (composed of the ExB drift and the phase velocity of turbulence v ⊥ = v E×B +v ph ), with Doppler reflectometry measurements, and with neoclassic fluid calculations. An important condition for the application of the method is the presence of turbulence with sufficiently long decorrelation time. It is shown that at the shear layer the decorrelation time is reduced, limiting the application of the method. The magnetic field pitch angle measured by this method shows the expected dependence on the magnetic field, plasma current and radial position. The profile of the pitch angle reproduces the expected shape and values. However, a comparison with the equilibrium reconstruction code cliste suggests an additional inclination of turbulent eddies at the pedestal position (2-3• ). This additional angle decreases towards core and at the edge.

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Section: Time Delay Estimation In Tokamaksmentioning

confidence: 90%

Magnetic field pitch angle and perpendicular velocity measurements from multi-point time-delay estimation of poloidal correlation reflectometry

Prisiazhniuk

Krämer–Flecken

Happel

et al. 2017

Plasma Phys. Control. Fusion

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“…One Frequency Scan It is therefore necessary to use a better method taking into account the width of the ACF and CCF and which can be applied in the shear layer as well. The elliptical model invented by Briggs [4] and Phillips [5] and applied for in the interpretation of plasma or fluid instabilities [6] and for turbulent shear flows by He [14] based on the assumption that iso-correlation surfaces have elliptical shape and allow to relate the cross correlation obtained for a certain ∆t and a poloidal distance s to the auto correlation at a certain time lag τ. In this model the propagation velocity is given as:…”

Section: 12mentioning

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 brackets <> represent ensemble averages. The cross-power spectrum is defined as the sum of co (C xy ) and quad (Q xy ) spectra [26] …”

Section: Correlation and Coherence Analysismentioning

confidence: 99%

Localization of MHD and fast particle modes using reflectometry in ASDEX Upgrade

Graca¹,

Conway²,

Lauber³

et al. 2007

Plasma Phys. Control. Fusion

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Abstract. The radial structure of Toroidal Alfvén Eigenmodes (TAEs) is of great importance for comparison with theoretical predictions. A dual-channel fast frequency hopping millimeter-wave reflectometer installed on the ASDEX Upgrade tokamak is capable of measuring density fluctuations from the plasma edge to core, allowing the radial eigenfunction of n = 4 TAE and edge MHD modes to be obtained using phase perturbation and coherence data analysis techniques. The two techniques reveal similar results, and in particular the radial structure of the n = 4 TAE is found to be in good agreement with numerical predictions from linear gyrokinetic simulations. First results of the radial localization of Alfvén cascades are also presented.

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Digital signal processing techniques for plasma dispersion curve measurements

Cited by 10 publications

References 14 publications

Magnetic field pitch angle and perpendicular velocity measurements from multi-point time-delay estimation of poloidal correlation reflectometry

Magnetic field pitch angle and perpendicular velocity measurements from multi-point time-delay estimation of poloidal correlation reflectometry

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

Localization of MHD and fast particle modes using reflectometry in ASDEX Upgrade

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