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  • 1
    Digitale Medien
    Digitale Medien
    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
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1149499
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  • 2
    Digitale Medien
    Digitale Medien
    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
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1149424
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  • 3
    Digitale Medien
    Digitale Medien
    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
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1149498
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  • 4
    Digitale Medien
    Digitale Medien
    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
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1149493
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  • 5
    Digitale Medien
    Digitale Medien
    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
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1148676
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  • 6
    Digitale Medien
    Digitale Medien
    Ultrafast broadband frequency-modulation reflectometer for density profile measurements in GAMMA 10 : 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. 443-445 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: A broadband microwave reflectometer was applied to the GAMMA 10 tandem mirror using a fast-sweep hyperabrupt varactor-tuned oscillator (HTO) that can be swept over the full band (12–18 GHz) in less than 5 μs. Clear fringes are observed during a plasma shot when the resultant frequencies from the reflectometer output are much larger than the ion cyclotron range of frequency (3–10 MHz). The density profile measurement is performed for various sweep times of HTO from 1 ms to 5 μs in which two reconstruction methods are utilized, zero-cross counting of the fringes and frequency analysis using the maximum entropy method. The reliability of the profile measurement seems to be improved when the sweep time is faster than 10–30 μs. The integrated value of many reconstructed density profiles agrees well with the profile obtained from a scanning interferometer. The fast-sweep reflectometer is also applied to the measurement of density fluctuations such as plasma movement as well as density profiles. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1147601
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  • 7
    Digitale Medien
    Digitale Medien
    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
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1147905
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  • 8
    Digitale Medien
    Digitale Medien
    Heterodyne O-mode reflectometer on the JT-60U tokamak (2002)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 73 (2002), S. 1169-1176 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: A three-channel heterodyne O-mode reflectometer system has been developed for density fluctuation measurements on the JT-60U tokamak. The system consists of one fixed channel with a frequency of 34 GHz and two selectable frequency channels with frequencies in the range of 34–40 and 48–50 GHz in order to measure the change of fluctuation amplitude, fluctuation coherence, and movement of the cutoff layer during the discharge. The reflectometer system has now become a standard diagnostic for density fluctuation measurements on JT-60U covering both core and edge plasma regions. The capabilities of the system are illustrated for three experimental cases: edge transport barriers in H-mode plasmas, internal transport barriers in reversed shear plasmas, and fast turbulence burst at the onset of multifaceted asymmetric radiation from the edge. © 2002 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1445867
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  • 9
    Digitale Medien
    Digitale Medien
    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
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1149423
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  • 10
    Digitale Medien
    Digitale Medien
    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
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1147764
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