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  • 1
    Digitale Medien
    Digitale Medien
    Simulations of beam-emission spectroscopy on Alcator C-Mod (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. 987-987 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: An eight-channel beam-emission-spectroscopy (BES)1 system has been installed on the Alcator C-Mod tokamak, intended for use with a diagnostic neutral hydrogen beam (DNB). Capable of localized measurements from the plasma edge to the plasma core, the BES diagnostic collects light from the first Balmer transition (Hα) resultant from beam/plasma collisions. The Hα line splits into several components whose central wavelengths depend on the viewing geometry, the magnetic field, and the beam energy. This is due to the Doppler shifts from viewing the beam off perpendicular, the different velocities of the three mass components of the beam (H, H2, H3), and the large motional Stark effect. Optimal signal-to-noise requires collecting these components while attenuating all other emission: primarily bremsstrahlung and Dα radiation (from plasma D0/e− collisions). Tunable bandpass filters are thus required. A BES simulation code has been developed that calculates the brightnesses (bremsstrahlung, Dα, Hα) versus wavelength using plasma profile data from the C-Mod MDSplus database,2 a computation of the beam penetration, the viewing and DNB geometries, and bandpass filter characteristics. The model was first used to estimate signal levels and choose the optimal BES bandpass filters; its ultimate purpose is to determine the shot-to-shot tuning requirements of the filters for different discharge conditions. Comparisons of measured and predicted background bremsstrahlung and Dα brightnesses are presented, as are first measurements and calculations of the beam emission. The code is written in the IDL programming language3 utilizing the "widget" graphical user interface. Designed for geometrical and spectral flexibility, it can be modified to simulate other beam diagnostics such as motional-Stark-effect plasma current measurements and charge-exchange recombination spectroscopy, as well as passive diagnostics measuring chord-averaged spectral emission. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1326010
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  • 2
    Digitale Medien
    Digitale Medien
    Neutral beam diagnostics for Alcator C-Mod : 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. 300-303 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: A diagnostic neutral beam will be installed on Alcator C-Mod for measurement of ñi, nz, Tz, vθ, vcursive-phi, and j. The beam will be used primarily for the study of thermal transport, Er in H-mode discharges, and to provide critical profile and turbulence data for tests of theoretically based models of turbulence and transport. The beam selected for this work was used on Texas Experimental Tokamak and is rated at 50 kV and 6 A of extracted current in hydrogen. It can produce beams of deuterium or helium as well. It is currently being reconfigured for installation on C-Mod. Capabilities for the intended measurements are described using simulations based on measured C-Mod profiles. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1147854
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  • 3
    Digitale Medien
    Digitale Medien
    High-sensitivity, high-resolution measurements of radiated power on TEXT-U : Proceedings of the tenth topical conference on high temperature plasma diagnostics (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 549-551 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Investigations of a possible radiation drive of edge turbulence in tokamaks require sensitive radiated power measurements having high temporal and spatial resolution. A commercially available 16-element X–UV-enhanced photodiode array having essentially 100% quantum efficiency from ∼25 to ≥6 keV is used. The frequency response is presently limited by the amplifiers to ∼50 kHz, although the ultimate response is expected to be much higher ((approximately-greater-than)200 kHz). Each element's view is ∼0.4 cm wide along the major radius at the plasma midplane while the view of the entire array is ∼6.3 cm wide and is scannable over the entire plasma cross section. The details of the system as well as observations of fine spatial structures and fluctuations undetectable by conventional bolometers are presented. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1146348
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  • 4
    Digitale Medien
    Digitale Medien
    Cross-correlation techniques applied to chord-integrated measurements (abstract)a) : Proceedings of the tenth topical conference on high temperature plasma diagnostics (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 460-460 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: In an effort to determine the effects of impurities on turbulence in the edge plasma of tokamaks (electron temperature and radiative cooling rate out of phase), we would like to cross-correlate local measurements of T˜e and p˜rad. The former is provided by Langmuir probes.c) Unfortunately, only chord-integrated radiated power is available, provided by a high-resolution scannable X-UV array.d) We orient one channel of the array to intersect the flux tube sampled by the probe (taking advantage of the long parallel correlation lengths) and cross-correlate the signals in an attempt to extract the portion of the radiation signal eminating from the probe location. Preliminary results indicate a statistically significant level of correlation. A model for cross correlating a chord-integrated signal with a local signal is studied to aid the interpretation of the experimental results. If successful, this technique has important ramifications generally in that it effectively converts a chord-averaged measurement into a local one. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1146381
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  • 5
    Digitale Medien
    Digitale Medien
    Inversion of chord-integrated data from noncircular tokamak plasmas (abstract)a) : Proceedings of the tenth topical conference on high temperature plasma diagnostics (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 460-460 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: The superior performance of diverted and elongated plasmas in tokamaks motivates improvements of inversion techniques for chord integrated data (from interferometry, spectroscopy, bolometry, etc.) from such noncircular plasmas. We present a technique planned for TEXT-U. First, flux-surface contours are calculated using EFIT or a filament code. A computer subroutine is provided which then computes, for a given chord, the length of the chord segment enclosed within the flux surface ψ, as a function of ψ from the tangent surface ψtan outward. Using the length functions, the inversions may be performed using the technique of Park or by least-squares fitting. Inversions of FIR interferometer data are presented. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1146382
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  • 6
    Digitale Medien
    Digitale Medien
    Charge-exchange recombination spectroscopy and beam-emission spectroscopy for C-Mod : 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. 882-885 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: The design of two beam-based diagnostic systems for C-Mod, charge-exchange recombination spectroscopy (CXRS) and beam-emission spectroscopy (BES) will be presented. A 50-keV diagnostic neutral beam (DNB) will be installed on C-Mod for these and other diagnostics. By adding BES and CXRS to the set of C-Mod diagnostics, it will be possible to test theory-based models of turbulent transport, which are typically based on marginal stability and the existence/dominance of ion temperature gradient (ITG) modes. Tests that coordinate turbulence measurements with transport measurements are largely unavailable at present. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1149461
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  • 7
    Digitale Medien
    Digitale Medien
    A study for the installation of the TEXT heavy-ion beam probe on DIII-D : 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. 320-323 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: An assessment of the feasibility of installing the TEXT 2 MeV heavy-ion beam probe on the DIII-D tokamak has been completed. Detailed drawings of the machine cross section were imported into the CAD application AutoCAD. A set of programs written in AutoLisp were used to generate trajectories. Displays of the accessible cross section of the plasma, scan lines for the entire range of primary beam energy and injection angle ranges, and sample–volume dimensions can be rapidly generated. Because of the large deflection between the primary input beam and the emergent secondary beam, either the analyzer needs to be tracked over a ±20° angle or secondary poloidal deflector plates need to be installed at the exit port. Toroidal deflector plates will be installed at both the injection and exit ports to compensate for toroidal displacements and deflections. The sample volumes generated by this procedure are within a few centimeters of the locations derived from a full three-dimensional calculation.© 1997 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1147860
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  • 8
    Digitale Medien
    Digitale Medien
    Effects of limited spatial resolution on fluctuation measurements (invited) : Proceedings of the tenth topical conference on high temperature plasma diagnostics (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 802-805 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: The finite sample volumes of fluctuation diagnostics distort the measurements not only by averaging the gross fluctuation parameters over the sample volumes, but more importantly (except for collective scattering), by attenuating the shorter wavelength components. In this work, the response of various sample volume sizes and orientations to a model fluctuation power spectrum S(k,ω) are examined. The model spectrum is fashioned after observations by far-infrared scattering on TEXT. The sample-volume extent in the direction of propagation of the turbulence is shown to be the most critical—not only does it reduce the measured fluctuation amplitude and increase the correlation length (as does an extent perpendicular to the propagation direction), but it also reduces the measured mean frequency and increases the apparent average phase velocity of the fluctuations. The differing sizes, shapes, and orientations of the sample volumes among fluctuation diagnostics, as well as deliberate variations within a single diagnostic, provide information on the form of the underlying turbulence and can be exploited to refine the model. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1146226
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  • 9
    Digitale Medien
    Digitale Medien
    Poloidal asymmetry and gradient drive in core electron density and temperature fluctuations on the Texas Experimental Tokamak-Upgrade (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 2013-2021 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Electron temperature and density fluctuations are measured in the core of the Texas Experimental Tokamak-Upgrade (TEXT-U) [P. H. Edmonds, E. R. Solano, and A. J. Wootton, in Proceedings of the 15th Symposium on Fusion Technology, Utrecht (Elsevier Science, Amsterdam, 1989), Vol. 1, p. 342] plasma across the poloidal cross section. The high spatial resolution of the heavy-ion beam probe (HIBP) and correlation radiometry of electron cyclotron emission (CRECE) reveal that both the density and temperature fluctuations are strongly poloidally asymmetric. Temperature fluctuation measurements indicate a broadband drift wave feature localized near the plasma equatorial plane on both the high- and low-field sides, which is consistent with density fluctuation measurements by far infrared (FIR) scattering. In contrast, the HIBP observes this feature localized only to the low-field side. Excellent spatial resolution allows us to investigate whether changes in the gradient affect the fluctuation amplitudes. We find that indeed, the temperature fluctuations increase with the electron temperature gradient. Results also link density fluctuations to changes in the density gradient. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.871998
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  • 10
    Digitale Medien
    Digitale Medien
    Experimental evidence of long-range correlations and self-similarity in plasma fluctuations : The 40th annual meeting of the division of plasma physics of the american physical society (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 1885-1892 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: To better understand long time transport dynamics, techniques to investigate long-range dependences in plasma fluctuations have been applied to data from several confinement devices including tokamaks, stellarators, and reversed field pinch. The results reveal the self-similar character of the edge plasma fluctuations. This implies that the tail of the autocorrelation function decays as a power law and suggests that there is a superdiffusive component of the anomalous transport. Rescaled fluctuation and turbulent flux spectra from different devices also show a strong similarity. For a range of parameters corresponding to the tokamak ohmic regime and equivalent power for other devices, the spectral decay index may show a universal character.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.873490
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