Correlation reflectometry at TEXTOR

Krämer‐Flecken, A.; Soldatov, S.; Vowinkel, B.; Müller, Patrick

doi:10.1063/1.3497305

Cited by 34 publications

(39 citation statements)

References 12 publications

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“…Variations in the phase of the reflected microwave beams are related to movements in the density cutoff iso-layers, from which density fluctuations can be estimated [21]. By cross-correlating the reflectometer signals from arbitrary antennas pairs properties of the density fluctuation, such as the correlation length (l ⊥ ), decorrelation time (τ d ) and the fluctuation propagation velocity (v ⊥ ) can be obtained [22,23,24,25,26], and in addition the field-line pitch angle [27].…”

Section: Poloidal Correlation Reflectometrymentioning

confidence: 99%

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: Poloidal Correlation Reflectometrymentioning

confidence: 99%

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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“…It is an ideal tool to study the two-dimensional structure of the turbulence with the potential to derive the safety-factor profile [9]. An important global aspect of turbulence is the poloidal asymmetry of the fluctuations which is addressed with two multi-channel O-mode reflectometer systems installed on the low and high-field sides of AUG [10].…”

Section: Interactionmentioning

confidence: 99%

Experimental turbulence studies for gyro-kinetic code validation using advanced microwave diagnostics

et al. 2015

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Abstract. For a comprehensive comparison with theoretical models and advanced numerical turbulence simulations, a large spectrum of fluctuation parameters were measured on the devices ASDEX Upgrade, TCV, and Tore-Supra. Radial profiles of scale-resolved turbulence levels in H-mode discharges are measured and compared with GENE simulations in the transition range from ion-temperature-gradient to trappedelectron-mode turbulence. Correlation reflectometry is used to study the microscopic structure of turbulence and GAMs in discharges where poloidal flow damping was varied by means of variations of the shape of the poloidal plasma cross-section and collisionality. The aspects of turbulence spreading and non-local transport in response of local changes in density and temperature gradients are studied during phases with ECRH power modulation by means of radial correlation measurements and an ultrafast reflectometer. Full-wave codes and synthetic diagnostics are applied for the interpretation of the data.

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“…Indeed, the several antenna arrays installed at different poloidal and toroidal locations [31] allow to perform shortrange poloidal correlation and long-range toroidal correlation.…”

Section: Perpendicular Velocity and Normalized Scale Of Qc-temmentioning

confidence: 99%

“…This analysis uses conventional reflectometers to study density fluctuation in TEXTOR [31], Tore Supra [32] and JET [33,34]. Their main properties are summarized in table 1 and an example of ray tracing is shown for each reflectometer in figure 1.…”

Section: Diagnostics Set-upmentioning

confidence: 99%

Discriminating the trapped electron modes contribution in density fluctuation spectra

et al. 2015

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Quasi-coherent (QC) modes have been reported for more than 10 years in reflectometry fluctuations spectra in the core region of fusion plasmas. They have characteristics in-between coherent and broadband fluctuations as they oscillate at a marked frequency but have a wide spectrum. This work presents further evidences of the link recently established between QC modes and the trapped electron modes (TEM) instabilities (Arnichand et al 2014 Nucl. Fusion 54 123017). In electron cyclotron resonance heated discharges of Tore Supra, an enhancement of QC modes amplitude is observed in a region where TEM cause impurity transport and turbulence. In JET Ohmic plasmas, QC modes disappear during density ramp-up and current ramp-down. This is reminiscent of Tore Supra and TEXTOR observations during transitions from the linear Ohmic confinement (LOC) to the saturated Ohmic confinement (SOC) regimes. Evidencing TEM activity then becomes experimentally possible via analysis of fluctuation spectra.

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Correlation reflectometry at TEXTOR

Cited by 34 publications

References 12 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

Experimental turbulence studies for gyro-kinetic code validation using advanced microwave diagnostics

Discriminating the trapped electron modes contribution in density fluctuation spectra

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