758 research outputs found
Analysis and separation of time-frequency components in signals with chaotic behavior
Working document. Unpublished.The analysis of chaotic signals with time-frequency methods is considered. For this purpose, two new transformations are presented which consist in the decomposition of a signal onto an orthogonal set of respectively linear and hyperbolic chirps. The linear chirp transformation is able to discriminate and extract particular chaotic components in non-stationary square integrable signals. This is demonstrated in an example studying the reflectometry measures of a turbulent plasma. The hyperbolic chirp transformation is designed for the detection and extraction of chaotic parts in self-similar processes such as stochastic motions. Mathematical connections are made between these two methods and other well-known transformations
Plasma turbulence measured by fast sweep reflectometry on TORE SUPRA
Traditionally devoted to electron density profile measurement we show that
fast frequency sweeping reflectometry technique can bring valuable and
innovative measurements onto plasma turbulence. While fast frequency sweeping
technique is traditionally devoted to electron density radial profile
measurements we show in this paper how we can handle the fluctuations of the
reflected signal to recover plasma density fluctuation measurements with a high
spatial and temporal resolution. Large size turbulence related to
magneto-hydrodynamic (MHD) activity and the associated magnetic islands can be
detected. The radial profile of the micro-turbulence, which is responsible for
plasma anomalous transport processes, is experimentally determined through the
fluctuation of the reflected phase signal.Comment: 12th International Congress on Plasma Physics, 25-29 October 2004,
Nice (France
On non-zero space average density perturbation effects in tokamak plasma reflectometer signals
12th International Congress on Plasma Physics, 25-29 October 2004, Nice (France)The effects of the non-zero average density perturbation on phase and amplitude measured by reflectometry are presented. The non-zero average density perturbation on the phase variation can be seen as an index effect as soon as the shape of the density perturbation does not introduce spectral effects. Amplitude modulation in time follows generally the properties of the cut-off layer seen as a mirror but some specific situations produce a time modulation two times higher than the input time variation of the density perturbation as observed in Tore Supra. The introduction of secondary cut-off can exhibit this effect as shown in 2D simulations
Tomographic analysis of reflectometry data II: the phase derivative
A tomographic technique has been used in the past to decompose complex
signals in its components. The technique is based on spectral decomposition and
projection on the eigenvectors of a family of unitary operators. Here this
technique is also shown to be appropriate to obtain the instantaneous phase
derivative of the signal components. The method is illustrated on simulated
data and on data obtained from plasma reflectometry experiments in the Tore
Supra.Comment: 25 pages, Latex, 17 figure
Spatial and Wavenumber Resolution of Doppler Reflectometry
Doppler reflectometry spatial and wavenumber resolution is analyzed within
the framework of the linear Born approximation in slab plasma model. Explicit
expression for its signal backscattering spectrum is obtained in terms of
wavenumber and frequency spectra of turbulence which is assumed to be radially
statistically inhomogeneous. Scattering efficiency for both back and forward
scattering (in radial direction) is introduced and shown to be inverse
proportional to the square of radial wavenumber of the probing wave at the
fluctuation location thus making the spatial resolution of diagnostics
sensitive to density profile. It is shown that in case of forward scattering
additional localization can be provided by the antenna diagram. It is
demonstrated that in case of backscattering the spatial resolution can be
better if the turbulence spectrum at high radial wavenumbers is suppressed. The
improvement of Doppler reflectometry data localization by probing beam focusing
onto the cut-off is proposed and described. The possibility of Doppler
reflectometry data interpretation based on the obtained expressions is shown.Comment: http://stacks.iop.org/0741-3335/46/114
Characterizations and first plasma operation of the WEST load-resilient actively cooled ICRF launchers
The paper discusses the characterization of the three high power steady-state and load-resilient ICRF launchers of WEST before their installation in the tokamak. These launchers have been characterized and validated in low-power experiments (milliwatt range) as well as in experiments at the nominal RF voltages and currents in the TITAN vacuum chamber (~30 kV and 915 A peak). The successful commissioning of two of the launchers during the WEST C3 campaign at ~1 MW power level is illustrated. Manual and real-time controlled impedance-matching of the launchers are discussed, as well as the validation of their load-resilience. Furthermore, several redundant and complementary protection systems have been validated and are reviewed in the paper
A tomographic analysis of reflectometry data I: Component factorization
Many signals in Nature, technology and experiment have a multi-component
structure. By spectral decomposition and projection on the eigenvectors of a
family of unitary operators, a robust method is developed to decompose a
signals in its components. Different signal traits may be emphasized by
different choices of the unitary family. The method is illustrated in simulated
data and on data obtained from plasma reflectometry experiments in the tore
Supra.Comment: 27 pages Latex, 17 figure
Interaction of ITER-like ICRF antenna with Tore Supra plasmas: insight from modelling
The non-linear interaction of ion cyclotron resonance frequency (ICRF) waves with the plasma edge is one of the challenges faced by high power wave heating systems in next step devices. Such interaction is often associated with parallel RF electric fields excited by spurious parallel RF currents flowing on the antenna front face I -Experimental results 1 -ICRF antenna configurations. The prototype launcher ITER-lik
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