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Title: Reflectometry: A Reliable And Sensitive Plasma Diagnostic For Density Profile And Turbulence Measurements On Tore-Supra

Abstract

A set of four reflectometers has been installed on Tore-Supra to measure the density profiles and the properties of density fluctuations with good spatial resolution. Fast swept X-mode reflectometers covering the range 50 to 155 GHz provide reliable and accurate measurements of the whole density profile from the edge on the outer side up to the core on the high field side even during large and fast profile evolution. Precise evaluation of the density profile is crucial for particle transport studies. A particular feature, a local peaking, has been observed in the core during ohmic discharge. Density fluctuations are measured with three different techniques. The classical fixed frequency method looks at large scale fluctuations (kr < 3 cm-1) . It measures the radial profile of fluctuations and can detect density perturbation associated to high frequency modes. A new method has been validated to measure the radial profile of small scale density fluctuations from fast FM-CW phase reflected signal. This method could also retrieve the radial wavenumber spectrum. The last method Doppler reflectometry is based on back scattering. It measures the poloidal rotation and fluctuations amplitude at different poloidal wave numbers (3 < k{theta} < 20 cm-1). This collection of diagnosticsmore » achieves complementary measurements from the low to the high field side of the discharge and from large to small scale.« less

Authors:
; ; ; ; ;  [1]; ; ;  [2];  [3];  [4]
  1. Association Euratom-CEA, CEA/DSM/DRFC, Centre de Cadarache, 13108 Saint Paul lez Durance (France)
  2. LPTP, CNRS (UMR-7648), Ecole Poly technique, 91128 Palaiseau (France)
  3. LPMIA, Universite Henri Poincare, BP 239, 54506 VANDOEUVRE Cedex (France)
  4. LPIIM, CNRS (UMR 6633) -- Universite de Provence, 13397 Marseille Cedex 20 (France)
Publication Date:
OSTI Identifier:
20797879
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Conference Proceedings; Journal Volume: 812; Journal Issue: 1; Conference: PLASMA 2005: International conference on research and applications of plasmas; 3. German-Polish conference on plasma diagnostics for fusion and applications; 5. French-Polish seminar on thermal plasma in space and laboratory, Opole-Turawa (Poland), 6-9 Sep 2005; Other Information: DOI: 10.1063/1.2168805; (c) 2006 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; AMPLITUDES; BACKSCATTERING; DISTURBANCES; FLUCTUATIONS; GHZ RANGE; MICROWAVE RADIATION; PLASMA; PLASMA DENSITY; PLASMA DIAGNOSTICS; PLASMA RADIAL PROFILES; RADIATION TRANSPORT; ROTATION; SPATIAL RESOLUTION; TORE SUPRA TOKAMAK; TURBULENCE

Citation Formats

Sabot, R., Clairet, F., Giacalone, J. C., Molina, D., Sirinelli, A., Vermare, L., Hennequin, P., Honore, C., Truc, A., Heuraux, S., and Leclert, G.. Reflectometry: A Reliable And Sensitive Plasma Diagnostic For Density Profile And Turbulence Measurements On Tore-Supra. United States: N. p., 2006. Web. doi:10.1063/1.2168805.
Sabot, R., Clairet, F., Giacalone, J. C., Molina, D., Sirinelli, A., Vermare, L., Hennequin, P., Honore, C., Truc, A., Heuraux, S., & Leclert, G.. Reflectometry: A Reliable And Sensitive Plasma Diagnostic For Density Profile And Turbulence Measurements On Tore-Supra. United States. doi:10.1063/1.2168805.
Sabot, R., Clairet, F., Giacalone, J. C., Molina, D., Sirinelli, A., Vermare, L., Hennequin, P., Honore, C., Truc, A., Heuraux, S., and Leclert, G.. Sun . "Reflectometry: A Reliable And Sensitive Plasma Diagnostic For Density Profile And Turbulence Measurements On Tore-Supra". United States. doi:10.1063/1.2168805.
@article{osti_20797879,
title = {Reflectometry: A Reliable And Sensitive Plasma Diagnostic For Density Profile And Turbulence Measurements On Tore-Supra},
author = {Sabot, R. and Clairet, F. and Giacalone, J. C. and Molina, D. and Sirinelli, A. and Vermare, L. and Hennequin, P. and Honore, C. and Truc, A. and Heuraux, S. and Leclert, G.},
abstractNote = {A set of four reflectometers has been installed on Tore-Supra to measure the density profiles and the properties of density fluctuations with good spatial resolution. Fast swept X-mode reflectometers covering the range 50 to 155 GHz provide reliable and accurate measurements of the whole density profile from the edge on the outer side up to the core on the high field side even during large and fast profile evolution. Precise evaluation of the density profile is crucial for particle transport studies. A particular feature, a local peaking, has been observed in the core during ohmic discharge. Density fluctuations are measured with three different techniques. The classical fixed frequency method looks at large scale fluctuations (kr < 3 cm-1) . It measures the radial profile of fluctuations and can detect density perturbation associated to high frequency modes. A new method has been validated to measure the radial profile of small scale density fluctuations from fast FM-CW phase reflected signal. This method could also retrieve the radial wavenumber spectrum. The last method Doppler reflectometry is based on back scattering. It measures the poloidal rotation and fluctuations amplitude at different poloidal wave numbers (3 < k{theta} < 20 cm-1). This collection of diagnostics achieves complementary measurements from the low to the high field side of the discharge and from large to small scale.},
doi = {10.1063/1.2168805},
journal = {AIP Conference Proceedings},
number = 1,
volume = 812,
place = {United States},
year = {Sun Jan 15 00:00:00 EST 2006},
month = {Sun Jan 15 00:00:00 EST 2006}
}
  • Reflectometry is a versatile diagnostic which allows both electronic density profile and density fluctuation measurements. Fast sweep heterodyne technique is particularly suitable for precise measurement of the phase of the reflected signal, which records the story of the wave propagation through the plasma up to the cutoff layer, including the density fluctuations. The present article exhibits a comparison of the density fluctuation radial profile measurements between fast sweep frequency technique, both using O-mode and X-mode polarizations, and fixed frequency technique. The correct agreement between all measurements of the relative values of the density fluctuation profiles reinforces the validity of themore » approximations used.« less
  • Tore Supra is equipped with two 20 {mu}s fast sweep X-mode reflectometers operating between 50-110 GHz dedicated to density profile determination and an X-mode fixed frequency reflectometer operating between 105-155 GHz for density fluctuation measurements. Heterodyne and sine-cosine detection provide measurements of the reflected signal with high sensitivity. Operating profile reflectometer in burst mode (5 {mu}s dead time between two consecutive sweeps) allows quasi-simultaneous measurements at fixed frequency over a broad frequency band. Thus, information on plasma fluctuations, such as magnetohydrodynamic (MHD) activity, up to 20 kHz as well as a radial localization of the modes is accessible. The temporalmore » evolution of the q=1 rational surface during sawtooth crash activity has been recorded in the plasma center with high spatial resolution. In addition, a direct comparison between signals associated with a central MHD mode from both profile and fluctuation reflectometers, positioned at different toroidal angles, allows one to determine the plasma toroidal velocity.« less
  • Reliable experimental determination of the mean effective charge (Z{sub eff}) of the plasma is of enormous importance for the impurity control in high temperature plasmas, allowing the performance of various discharge scenarios to be assessed and the benchmarking of model calculations, ideally accompanied by measurements of the Z{sub eff} profile. The Z{sub eff} is usually calculated using data from line-integrated visible bremsstrahlung measurements, electron density and temperature profiles, and the plasma geometry. On Tore Supra (TS) it had been noticed in the past that hot spots on the inner wall, MARFEs or supra thermal electrons can falsify the signal ofmore » the visible bremsstrahlung. More significant, however, was a systematic overestimation of the edge channels, giving unreasonably high edge Z{sub eff} values of 30 or even higher. The analysis of dedicated discharges in the present configuration of TS leads us to conclude that this is due to the influence of vessel wall reflections. A newly developed inversion method which takes reflections into account shows that the presence of reflections leads to an overestimation of the outer channels in the reconstruction of the Z{sub eff} profile. This is due to the larger relative contribution of the reflections on the edge channels due to the shorter path length through the plasma and the lower bremsstrahlung emission at the edge. We present a model which takes into account this effect and allows a correction procedure to be applied when calculating the Z{sub eff} profile. The TS data can be modeled assuming Lambertian (diffusive) reflections with a reflectivity coefficient of 20%-25%, which is in agreement with measurements of the reflectivity of the inner wall of the TS vacuum chamber.« less
  • Turbulence measurements in TORE SUPRA tokamak plasmas have been quantitatively compared to predictions by nonlinear gyrokinetic simulations. For the first time, numerical results simultaneously match within experimental uncertainty (a) the magnitude of effective heat diffusivity, (b) rms values of density fluctuations, and (c) wave-number spectra in both the directions perpendicular to the magnetic field. Moreover, the nonlinear simulations help to revise as an instrumental effect the apparent experimental evidence of strong turbulence anisotropy at spatial scales of the order of ion-sound Larmor radius.
  • An edge transport barrier is now one of the most important subjects of controlled fusion research. The edge transport barrier is located in the plasma region where hydrogen atoms readily penetrate, so the intensity of the H{sub {alpha}} (D{sub {alpha}}) line is high enough. A new diagnostic method uses the well-known property of hydrogen atoms that the ratio of the ionization rate S{sub i} to the excitation rate S{sub v} for the H{sub {alpha}} line is nearly constant over a wide range of plasma temperatures and densities. An expression has been derived that relates the radial profiles of the plasmamore » density and H{sub {alpha}} intensity. The use of charge coupled device detectors makes it possible to measure the radial profile of H{sub {alpha}} line intensity with a resolution {approx}0.1 cm; a high intensity of the H{sub {alpha}} line ensures a high time resolution {approx}1 ms. A high resolution is thus achieved for the density profile calculated from the H{sub {alpha}} intensity profile. The method was tested when studying the plasma density profile in the region of edge transport barrier in the L-2M stellarator. It has been shown that the density gradient varies during the barrier formation and that a fine structure of the density profile correlates with a character of the plasma transport near resonance magnetic flux surfaces.« less