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  • 1
    Electronic Resource
    Electronic Resource
    Recursive algorithm for fast evaluation of the Abel inversion integral in broadband reflectometry : Proceedings of the 12th topical conference on high temperature plasma diagnostics (1999)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 1047-1050 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The application of Kalman filtering is proposed for the numerical evaluation of plasma density profiles using noisy group delay data obtained from O-mode frequency-modulated broadband reflectometry. This method allows faster computation of the Abel inversion integral than the usual numerical methods (e.g., the trapezoidal rule) while maintaining a good accuracy in the presence of noise. In addition, density profiles with different degrees of smoothing can be produced by adjusting a single parameter. The algorithm seems promising in applications to plasma control in real time. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149306
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  • 2
    Electronic Resource
    Electronic Resource
    Microwave interferometer with a differential quadrature phase detection (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 2547-2551 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A single channel microwave interferometer has been developed for a tokamak with an improved detection that uses an heterodyne configuration and is based on a differential quadrature phase concept. With the new detection very sensitive and accurate direct phase measurements are obtained due to the elimination of the spurious variations of the detected signals resulting from the nonideal behavior of the output mixers. As a result, the line integrated density along the vertical central chord of the vacuum chamber can be determined during the whole plasma discharge. Fast density variations occurring both at the formation phase of the plasma and during sawtooth cycles could also be measured. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1145656
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  • 3
    Electronic Resource
    Electronic Resource
    Initialization of plasma density profiles from reflectometry (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 4937-4942 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The contribution of the initial plasma to density profiles reconstructed from the dφ/df vs f curve obtained with reflectometry is studied. It is shown that the initial phase information determines to a great extent the accuracy of the inverted profiles at the edge. As it is difficult to measure the edge contribution models are required to initialize the profile evaluation. A novel method is presented that uses the phase information from the lowest frequency waves to obtain dφ/df below the first probing frequency F1, by imposing the continuity with the measured dφ/df characteristic and its derivative at F1. An approximate shape of the edge profile is obtained because low-frequency waves are sensitive to the initial plasma where they propagate without reflection. The accuracy of the inverted profiles is thereby improved, as shown by simulation studies performed for profiles with an exponential-like decay and with an edge density plateau (typical of H-mode regimes during ELMs). It is found that the contribution from the initial plasma decreases with density (or frequency); for densities of the order of 10× the first probed density ne1 it is reduced to values less than 10% in the case of a profile with a flat edge and 2% for a peaked one. For ne(approximately-greater-than)10ne1 the profiles can be absolutely calibrated from reflectometry data alone with an accuracy of ±2 mm independent of the initialization model. The numerical study also shows that profile deviations resulting from insufficient phase derivative data, e.g., due to discrete probing, can be more significant than those originated by the initialization process. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146178
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  • 4
    Electronic Resource
    Electronic Resource
    Reflectometry on ITER : Proceedings of the eleventh topical conference on high temperature plasma diagnostics (1997)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 435-438 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Reflectometry will be used on ITER to measure the density profile in the main plasma and divertor regions, and to measure the plasma position and shape in order to provide a standby reference for the magnetic diagnostics in long pulse discharges. The high temperatures of the ITER core and the resultant significant relativistic downshift of the second-harmonic electron cyclotron absorption imply that both low-field side O-mode and high-field side lower cut-off (X−l mode) systems are required to access the full plasma profile. A low-field side upper cut-off (X−u mode) system will also be required for measurements of the scrape-off layer. For measurements of the plasma position and shape, an O-mode system is optimum due to the large range of magnetic field along the plasma periphery and the wide range of possible plasma configurations achievable on ITER. A robust real-time calibration technique of the whole transmission line is required. It is likely that an accurate estimate of the position of the plasma will require the simultaneous use of signals from the profile reflectometer. For the divertor, profiles with peak densities in the range 1019–1022/m3 are to be measured with a target resolution of 3 mm. The large density range will necessitate the use of more than one system. Installing these reflectometers on ITER incurs additional difficulties such as the routing of the millimetre wave radiation around the complicated first wall and divertor structures and design of antennas able to operate through the first wall and blanket. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1148220
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  • 5
    Electronic Resource
    Electronic Resource
    Ultrafast broadband frequency modulation of a continuous wave reflectometry system to measure density profiles on ASDEX Upgrade (1996)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 67 (1996), S. 4138-4145 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A reflectometry system has been developed for ASDEX Upgrade to measure the plasma profile from the scrape-off layer until the bulk plasma, simultaneously at the high and low field sides. Unique features of the system are the ultrafast broadband frequency modulation of a continuous wave using solid state stable hyper abrupt tuned oscillators (down to 10 μs), high and low field side channels and fully remote control operation, via optical fiber links. Due to the special design of the transmission line, with decoupled in going and out going lines and one-antenna configuration, the system is optimized for reception and spurious reflections are eliminated. The ultrafast operation guarantees that the effect of plasma turbulence is greatly reduced. Both features determine the high performance of the diagnostic. A dedicated data acquisition system handles the large amounts of data generated by the broadband operation. Recent developments include the operation of new channels and an automatic and accurate frequency calibration circuit. Also, advanced digital signal processing techniques were applied to obtain density profiles with high spatial and temporal (20 μs) resolutions under turbulent plasma regions, e.g., the scrape-off layer. Experimental results are presented showing the great sensitivity of the diagnostic to plasma radial movements and its tolerance to vertical movements of the plasma. Density profiles measured in ELMy regimes illustrate the capabilities of the diagnostic to detect fast profile changes. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147517
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  • 6
    Electronic Resource
    Electronic Resource
    Microwave reflectometry for turbulence studies on ASDEX upgrade (abstract) : Papers from the thirteenth topical conference on high temperature plasma diagnostics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 319-319 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The reflectometry system installed in the tokamak ASDEX Upgrade has 11 channels primarily aimed at profile measurements and two dedicated channels operating at fixed frequency to study density fluctuations. The channels used for profile measurements can also be operated at fixed frequency. In this article we describe the potential of the system to study important characteristics of the plasma turbulence, from combined fixed frequency and profile measurements (to localize the reflecting layers). The numerical tools used to treat fixed frequency data are briefly described. Using a set of similar discharges and the ability of the microwave reflectometry system to probe simultaneously different layers with several channels, we obtain the time evolution of the integrated power spectra of the different signals versus the minor radius of the plasma. In plasma with H-mode edge and internal transport barrier we could identify a zone at the plasma core and another at the edge with reduced fluctuation levels, coinciding with the increase of central electron temperature and the L–H transition, respectively. Before each barrier is established, the turbulence is observed to decrease at the lower frequency range and is enhanced at the higher frequencies. In modulation electron cyclotron resonance heating experiments similar modifications in turbulence spectra are observed and may be correlated with the modulation period. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1323468
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  • 7
    Electronic Resource
    Electronic Resource
    Portuguese research program on nuclear fusion (1994)
    Springer
    Journal of fusion energy 13 (1994), S. 263-269 
    Details
    ISSN: 1572-9591
    Keywords: Fusion ; tokamak ; plasma diagnostics ; microwave reflectometry ; edge physics ; transport
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract The Portuguese research program on nuclear fusion is presented. The experimental activity associated with the tokamak ISTTOK as well as the work carried out in the frame of international collaboration are summarized. Future plans are briefly described.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02215845
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