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  • 1
    Electronic Resource
    Electronic Resource
    Multifaceted asymmetric radiation from the edge-like asymmetric radiative collapse of density limited plasmas in the Large Helical Device (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 3861-3864 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Neutral beam injection heated discharges at the density limit in the Large Helical Device [O. Motojima, H. Yamada, A. Komori et al., Phys. Plasmas 6, 1843 (1999)] are terminated with asymmetric radiative collapse (ARC) exhibiting several properties in common with the MARFE (multifaceted asymmetric radiation from the edge) phenomenon: (1) A highly poloidally asymmetric radiation profile which is stronger on the inboard side. (2) This asymmetry is well correlated with the signal from the multichord interferometer. (3) Moreover, evidence from several diagnostics at different toroidal locations supports the possibility that ARC may be toroidally symmetric. However in contrast to MARFE, ARC is only observed in the period just prior to the quench of the plasma. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1390330
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  • 2
    Electronic Resource
    Electronic Resource
    Development of millimeter-wave two-dimensional imaging array : 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. 1003-1006 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A millimeter-wave two-dimensional imaging array has been developed for diagnostics of magnetically confined plasmas. It is applied to the plug cell of the GAMMA 10 tandem mirror, and measures time evolution of radial and axial line-density and electron cyclotron emission (ECE) profiles in one plasma shot. The monolithic-type GaAs Schottky diode detector having an antenna and built-in amplifier on a GaAs substrate is newly fabricated using monolithic microwave integrated circuit (MMIC) technology. This novel detector is developed to attain high frequency response up to submillimeter-wave region and wideband heterodyne characteristics, and is expected to be applied to ECE imaging in a large helical device. The response of the detector is compared with that of the hybrid-type detector using beam-lead Schottky barrier diodes. The first experimental result of the ECE measurement is reported using a heterodyne radiometer with the MMIC detector. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149424
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  • 3
    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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  • 4
    Electronic Resource
    Electronic Resource
    CO2 laser imaging interferometer on LHD : 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. 1089-1093 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A CO2 laser (λ=10.6 μm) imaging interferometer is designed for electron density profile and electron density fluctuation measurements on large helical device (LHD). The purposes of this diagnostic are reliable electron density monitor in high density operation (especially in pellet injection discharge), precise measurement of electron density profiles and observations of density fluctuations. By using a CO2 laser, refraction effect becomes negligible, and the interferometer promises to be free from fringe jumps at high density. We plan to get 5 mm spatial resolution, (56 ch for each of two 280 mm slab beams, 50 ch for one 250 mm and 16 ch for 80 mm crossed beam), 3×10−3 rad phase resolution and 200 kHz frequency response for the above purpose. And fluctuation will be studied within the wave number range of 7×10−3≤k≤0.6 mm−1. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1323247
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  • 5
    Electronic Resource
    Electronic Resource
    New type of digital phase linearizer for real-time interferometric measurement : 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. 1103-1106 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A new type of digital phase linearizer has been developed for real-time electron density measurement using a multichannel far-infrared (FIR) interferometer. The phase linearizer can measure phase shifts up to 640 fringes. The size of internal memory is 16 bits-2 Mwords and the sampling frequency of the waveform data is up to 1 MHz. The internal clock for the counter is selectable to 100 or 200 MHz and the frequencies of the input signals, i.e., the reference signal and the probe one, are around 1 MHz. In the performance test the resolution of the phase components is achieved at 1/100 fringes, which corresponds to the line integrated density of 9.0×1016 m−2. For real-time measurements the phase linearizer has digital-to-analog converter (DAC) output. The resolution of DAC output is 12 bits and the amplitude is ± 5 V. The density feedback system on the large helical device has been utilized. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1324742
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  • 6
    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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  • 7
    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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  • 8
    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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  • 9
    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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  • 10
    Electronic Resource
    Electronic Resource
    Millimeter-wave two-dimensional imaging array for the GAMMA 10 tandem mirror : 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. 500-503 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A millimeter-wave two-dimensional imaging array has been fabricated in order to diagnose the plug-cell plasma of the GAMMA 10 tandem mirror. The heterodyne system with two separate sources enables the measurement of density and electron cyclotron emission (ECE) in one plasma shot. The interferometer successfully measures the time evolution of the axial and radial line-density profiles with phase resolution less than 1/200 fringe and spatial resolution of 16 mm in the vertical direction and 5 mm in the horizontal one. It is shown that the Abel-inverted density profiles are changed due to the injection of electron-cyclotron-resonance heating at the plug/barrier cells and central cell. The axial and radial dependence of the second-harmonic ECE emitted from hot electrons produced in barrier region is observed simultaneously. The fluctuation spectra of the ECE signals are compared with those obtained from the far-forward scattering diagnostic system. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147764
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