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  • 1
    Electronic Resource
    Electronic Resource
    The effects of density fluctuation on density profile measurements using a broadband frequency modulated reflectometer : 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. 1068-1071 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Numerical simulations of frequency modulation (FM) reflectometry are carried out for the effects of density fluctuations on phase measurements. It is found that the fluctuation amplitude, the fluctuation frequency, the sweep time of a source, and the beat frequency of a mixer output play the important roles. The reliability of density profile measurement is investigated for various sweep times and local path lengths. It is demonstrated that the reconstructed density profiles seem to be improved when the sweep time is faster than 100 μs and the local path length is shorter than 1 m. The numerical simulations are compared with the experimental results obtained from a broadband FM reflectometer applied to the GAMMA 10 tandem mirror. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149499
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  • 2
    Electronic Resource
    Electronic Resource
    Application of one-dimensional Wentzel–Kramers–Brillouin approximation in microwave reflectometry of plasma density profiles (1998)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 69 (1998), S. 2184-2185 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The accuracy of the one-dimensional (1D) Wentzel–Kramers–Brillouin (WKB) profile reconstruction algorithm currently used in microwave reflectometry of fusion plasmas is investigated. Two experimental conditions beyond the applicability of the 1D WKB approximation are discussed: a plasma with steep density gradients and the case of strong divergence of the microwave beam. It is demonstrated, that the 1D procedure of profile reconstruction provides a fairly accurate estimate for both cases, despite the influence of abrupt density changes and multidimensional effects. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1148921
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  • 3
    Electronic Resource
    Electronic Resource
    Analytical simulation of microwave reflectometry of a plasma cylinder (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 4139-4144 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An analytical solution of a time-dependent two-dimensional (2D) full-wave equation is obtained for the case of microwave propagation in a plasma with axial symmetry. The 2D structure of the electromagnetic wave in a nonmagnetized plasma (or an ordinary wave in a magnetized plasma) is studied for the general case of arbitrary time dependence of the incident wave emitted by the horn. The solutions cover the cases of conventional microwave reflectometry as well as the ultrashort pulse reflectometry of fusion and processing plasma. Analytical expressions can be further applied to study plasma density fluctuations as well as effects of plasma curvature and multidimensionality. The 2D plasma cylinder model is deemed by the authors to be more realistic as compared to the one-dimensional plasma slab model previously employed in all the analytical and most numerical treatments since the plasma in the fusion toroidal devices, mirror machines, and plasma processing chambers can be considered axially symmetric on the scale relevant to microwave reflectometry. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1409570
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  • 4
    Electronic Resource
    Electronic Resource
    Preliminary electron density profile and fluctuation measurements on GAMMA 10 using ultrashort-pulse 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. 1042-1045 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The use of ultrashort pulses (full width at half-maximum=1–100 ps) as a source of broadband, time-resolved radiation has high potential for application in microwave diagnostics for fusion plasmas. Here we report on the ultrashort-pulse reflectometry system developed for electron density profile and fluctuation measurements on the GAMMA 10 tandem mirror. The four-channel system (selectable frequencies of 8–17 GHz at 1 GHz intervals) measures the double-pass time-of-flight from the vacuum window to the cutoff layer. The hardware has an uncertainty of ±40 ps and can be operated at a repetition rate of 400 kHz. The system is operational, however, data from plasma experiments is unavailable at the moment. Results from a single-channel O-mode system show time-of-flight measurements consistent with values calculated from profiles obtained by a scannable single-channel interferometer. Fluctuation measurements are also consistent with results from a Fraunhofer diffraction diagnostic. These results suggest that with further refinements, ultrashort- pulse reflectometry will yield a simple yet reliable diagnostic for fusion devices. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149498
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  • 5
    Electronic Resource
    Electronic Resource
    Wavelet analysis of plasma fluctuations in microwave 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. 1052-1055 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A time–frequency analysis of plasma turbulence is performed for the GAMMA10 tandem mirror plasma. The method is based on the decomposition of the reflectometer signal into a set of wavelets. Excellent resolution in the time–frequency domain, inherent to wavelet analysis, allowed us to observe fast changes in the instantaneous spectra of fluctuations, which would be averaged out if treated using conventional Fourier analysis. In order to estimate the propagation velocity of turbulent fluctuations, a wavelet cross-correlation function was calculated. Comparison of wavelet spectra, corresponding to different reflectometer channels, demonstrates the existence of short-time flashes of fluctuation intensity, as well as elongation of low-frequency disturbances along the magnetic field lines and their rotation in the E×B direction. Plasma fluctuations in the Alfvén range of frequencies sometimes propagate from the center towards the magnetic plugs with velocities close to 1000 km/s. In general, the wavelet spectra of plasma turbulence in the Alfvén range of frequencies, viewed by means of the microwave reflectometer, appear to be much more irregular than the corresponding spectra of magnetic field fluctuations obtained using magnetic probes. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149493
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  • 6
    Electronic Resource
    Electronic Resource
    Measurement of plasma density using wavelet analysis of microwave reflectometer signal (1998)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 69 (1998), S. 425-430 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A new method of plasma density profile reconstruction in microwave reflectometry is proposed and implemented on an X-mode broadband reflectometer of the GAMMA 10 mirror device with an ultrafast sweep rate of 10–20 μs. The proposed method makes use of the wavelet transform of the detected signal. Excellent resolution in the time-frequency domain, inherent to wavelet analysis, allows one to obtain a radial electron density profile for every frequency sweep. The electron density reconstruction algorithm, besides the wavelet transform of the reflectometer signal, also includes the calibration, profile initialization, and the solution of an integral equation, ultimately yielding the local values of the electron density. Calibration of the measured signal phase and profile initialization is performed using the independent results of microwave interferometry. Inversion of the integral equation is implemented utilizing the gradient method, numerically stable even for plasma regions with steep density gradients and density profile plateaus. A wavelet-based profile reconstruction algorithm is especially advantageous for monitoring transient plasma phenomena and fast processes, such as in pellet injection, ultrafast swept reflectometry, and short pulsed reflectometry. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1148676
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  • 7
    Electronic Resource
    Electronic Resource
    Measurement of magnetic fluctuations of electromagnetic plasma waves by cross-polarization scattering : 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. 454-457 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The cross-polarization scattering (CPS) technique was applied to the GAMMA 10 tandem mirror for measurements of internal magnetic fluctuations associated with waves in the ion cyclotron range of frequency. The CPS is related to the mode-conversion effect consisting of a polarization difference of a scattered wave with regard to an incident wave. In GAMMA 10, the incident ordinary (extraordinary) wave is transferred to the extraordinary (ordinary) wave by magnetic field fluctuations near the cutoff layer of a plasma. The transferred wave penetrates through the cutoff layer and is detected. The frequency spectra and density and magnetic field fluctuations of the waves are evaluated from the CPS diagnostic and reflectometry. The ratio of the magnetic field to density fluctuation level depends on the phase velocity of the slow Alfvén wave. The CPS data are also compared with those obtained from magnetic probes. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147905
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  • 8
    Electronic Resource
    Electronic Resource
    Cross-polarization scattering from low-frequency electromagnetic waves in the GAMMA10 tandem mirror : 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. 991-994 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A cross-polarization scattering (CPS) diagnostic method was applied to the GAMMA10 tandem mirror in order to study electromagnetic plasma waves with frequency less than 10 MHz. In the CPS process, an incident ordinary (extraordinary) wave is converted to an extraordinary (ordinary) wave by magnetic fluctuations in a plasma. The frequency spectra, and the density and magnetic fluctuations of the waves can be evaluated from both the CPS and reflectometry. The converted wave propagates through the cutoff layer and reaches a different diagnostic port with a receiver horn. The observed waves are identified as the electromagnetic drift wave assuming the wave number matching condition. The low frequency waves nonlinearly coupled with the Alfven ion cyclotron waves are also observed with increase in the plasma pressure. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149423
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  • 9
    Electronic Resource
    Electronic Resource
    Modelling of neutral-gas releases into the earth's ionosphere (1988)
    Springer
    Pure and applied geophysics 127 (1988), S. 415-446 
    Details
    ISSN: 1420-9136
    Keywords: Active experiments ; chemical releases ; ionospheric modification
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract This paper discusses a mathematical model which is aimed at the interpretation of the effects by injections of chemically active gases into the ionosphere. A study is made of neutral-gas expansion processes as well as of processes associated with the formation of decreased plasma density regions, ionospheric ‘holes’. The spatial-temporal distribution of particles released during the transition to the diffusion regime is constructed using an approximate, analytic solution of the Boltzmann equation with the collision integral in the form of BGK, with proper allowance for gravitation and atmospheric inhomogeneity. The investigation of processes associated with the formation of ionospheric ‘holes’ is carried out using a numerical model of ionosphere-plasmasphere coupling, in which the transfer equations for charged components are integrated along geomagnetic field lines. The purpose of the model is to calculate the electron density and temperature, ion composition and emission of a disturbed region in the 6300 Å line at ionospheric and plasmaspheric heights.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00879820
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