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  • 1
    Electronic Resource
    Electronic Resource
    Multipoint Thomson scattering diagnostic for DIII-D (1988)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 59 (1988), S. 1467-1469 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The multipoint Thomson scattering diagnostic for DIII-D has been in operation since early 1987. Its capability of measuring electron temperatures as low as 50 eV at densities of a few times 1012 cm−3 and a spatial resolution of 1.4 cm in the plasma edge region has been essential in the study of H-mode plasmas. The major components of the diagnostic system consist of a 10-J ruby laser, many stages of funnel-shaped beam baffles, stacks of razor blades for viewing and stray light dumps, two wide-angle lenses for the collection of scattered light through reentrant window ports with protection shutters, 88 fiber bundles 15 m in length for light transmission to an f/1.9 spectrometer, an intensified CCD camera system capable of single-photon detection, and a VAX computer for hardware control and data processing. The input end of the fiber bundle is made demountable so the view locations can be reconfigured to optimize the spatial resolution for the plasma region of interest.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1139690
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  • 2
    Electronic Resource
    Electronic Resource
    Beyond paradigm: Turbulence, transport, and the origin of the radial electric field in low to high confinement mode transitions in the DIII-D tokamak (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 2397-2407 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The paradigm of shear suppression of turbulence as the mechanism for the low to high confinement mode (L to H) transition is examined by quantitative comparison of the predictions of the paradigm with experimental results from the DIII-D tokamak [Plasma Physics and Controlled Fusion Research (International Atomic Energy Agency, Vienna, 1986), p. 159]. The L to H transition trigger is V×B rotation, not the main ion pressure gradient. The radial electric field Er shear increases before the fluctuation suppression, consistent with increasing Er shear as the cause of the turbulence suppression. The spatial dependence of the turbulence reduction is consistent with shear suppression for negative Er shear. For positive Er shear, the turbulence suppression is consistent with the effect of Er curvature for modes for which an Er well is destabilizing. Finally, the transport barrier depends on the phase angle between the density and potential fluctuations inside the Er well, an effect not included in existing L to H transition models. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871263
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  • 3
    Electronic Resource
    Electronic Resource
    Measurements and implications of Zeff profiles on the DIII-D tokamak (1988)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 31 (1988), S. 3738-3743 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Here Zeff profiles have been obtained across the entire minor radius of the DIII-D [Fusion Technol. 8, 441 (1985); Plasma Physics and Controlled Nuclear Fusion Research, 1986 (IAEA, Vienna, 1987), Vol. 1, p. 159] tokamak from measurements of visible bremsstrahlung continuum radiation. The Zeff profiles are presented for Ohmic divertor and limiter plasmas as well as for neutral beam heated H-mode and L-mode plasmas. The measured Zeff profiles are found to have small gradients over the entire plasma cross section. This implies that resistivity gradient driven electrostatic modes are unlikely to influence the confinement properties in the edge region of these discharges. The H-mode plasma has a centrally peaked Zeff profile and a relatively flat electron density profile that suggests the existence of a negative value for the parameter ηi.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.866892
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  • 4
    Electronic Resource
    Electronic Resource
    Initial operation of the divertor Thomson scattering diagnostic 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. 1195-1200 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Thomson scattering measurements of ne and Te in the divertor region of a Tokamak are reported. These data are used as input to boundary physics codes such as UEDGE and DEGAS and to benchmark the predictive capabilities of these codes. These measurements have also contributed to the characterization of tokamak disruptions. A Nd:YAG laser (20 Hz, 1 J, 15 ns, 1064 nm) is directed vertically through the lower divertor region of the DIII–D Tokamak. A custom, aspherical collection lens (f/6.8) images the laser beam from 1 to 21 cm above the target plates into eight spatial channels with 1.5 cm vertical and 0.3 cm radial resolution. Two-dimensional mapping of the divertor region is achieved by sweeping the divertor X-point location radially through the fixed laser beam location. Fiber optics carry the light to polychromators whose interference filters have been optimized for low Te measurements. Silicon avalanche photodiodes measure both the scattered and plasma background light. Temperatures and densities are typically in the range of 5–200 eV and 1–10×1019 m−3, respectively. Low temperatures, Te〈1 eV, and high densities, ne〉8×1020 m−3 have been observed in detached plasmas. Background light levels have not been a significant problem. Reduction of the laser stray light permits Rayleigh calibration. Because of access difficulties, no in-vessel vacuum alignment target could be used. Instead, an in situ laser alignment monitor provides alignment information for each laser pulse. Results are compared with Langmuir probe measurements where good agreement is found except for regions of high ne and low Te as measured by Thomson scattering. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147893
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  • 5
    Electronic Resource
    Electronic Resource
    Design and operation of the multipulse Thomson scattering diagnostic on DIII-D (invited) : Proceedings of the 9th topical conference on high temperature plasma diagnostics (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 4901-4906 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: This paper describes the design and operation of a 40 spatial channel Thomson scattering system that uses multiple 20-Hz Nd:YAG lasers to measure the electron temperature and density profiles periodically throughout an entire plasma discharge. As many as eight lasers may be fired alternately for an average measurement frequency of 160 Hz, or they may be fired in rapid succession (〈10 kHz), producing a burst of pulses for measuring transient events. The high spatial resolution (1.3 cm) and wide dynamic range (10 eV–20 keV) enable this system to resolve large electron density and temperature gradients formed at the plasma edge and in the scrape-off layer during H-mode operation. These features provide a formidable tool for studying L–H transitions, edge localized modes (ELMs), beta limits, transport, and disruptions in an efficient manner suitable for large tokamak operation where shot-to-shot scans are impractical. The scattered light is dispersed by interference filter polychromators and detected by silicon avalanche photodiodes. Laser control and data acquisition are performed in real time by a VME-based microcomputer. Data analysis is performed by a MicroVAX 3400. Additional features of this system include real-time analysis capability, full statistical treatment of error bars based on the measured background light, and laser beam quality and alignment monitoring during plasma operation. Results of component testing, calibration, plasma operation, and error analysis are presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143545
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  • 6
    Electronic Resource
    Electronic Resource
    Initial operation of the divertor Thomson scattering diagnostic on DIII–D (abstract) : 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. 708-708 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The first Thomson scattering measurements of ne and Te in the divertor region of a tokamak are reported. These data are used as input to boundary physics codes such as UEDGE and DEGAS and to benchmark the predictive capabilities of these codes. These measurements have also contributed to the characterization of tokamak disruptions. A Nd:YAG laser (20 Hz, 1 J, 15 ns, 1064 nm) is directed vertically through the lower divertor region of the DIII–D tokamak. A custom, aspherical collection lens (f/6.8) images the laser beam from 1 to 21 cm above the target plates into eight spatial channels with 1.5 cm vertical and 0.3 cm radial resolution. Two-dimensional mapping of the divertor region is achieved by sweeping the divertor X-point location radically through the fixed laser beam location. Fiber optics carry the light to polychromators whose interference filters have been optimized for low-Te measurements. Silicon avalanche photodiodes measure both the scattered and plasma background light. Temperatures and densities are typically in the range of 5–200 eV and 1–10×1019 m−3, respectively. Low temperatures, Te〈1 eV, and high densities, ne〉8×108 cm−3 have been observed in detached plasmas. Background light levels have not been a significant problem. Reduction of the laser stray light permits Rayleigh calibration. Because of access difficulties, no in-vessel vacuum alignment target could be used. Instead, an in situ laser alignment monitor provides alignment information for each laser pulse. Results are compared with Langmuir probe measurements where good agreement is found except for regions of high ne and low Te as measured by Thomson scattering. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147680
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  • 7
    Electronic Resource
    Electronic Resource
    Progress on the multipulse Thomson scattering diagnostic on DIII-D : 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. 490-492 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The DIII-D Thomson scattering diagnostic, operational since 1990, uses 8 Nd:YAG 20-Hz lasers to measure electron temperature and density profiles (40 spatial points) throughout the plasma discharge. Recent progress has enabled a new set of operating modes to better fulfill varying plasma physics requirements. Custom circuitry for laser control (programmable with 1 μs precision) has successfully replaced a previous scheme which used real-time 68030 software. Two new modes of operation have been demonstrated. Burst mode is useful to study a transient plasma event: a series of laser pulses are fired at a rate ≤10 kHz after an external asynchronous event trigger. Burst mode is also useful to synchronize the Thomson lasers with other systems, such as an asynchronous Michelson ECE diagnostic scanning near 40 Hz. Group mode allows a programmed set of lasers to fire simultaneously into the same (65 ns) data acquisition gate. Improved signal/noise then yields smaller statistical errors in the profile results. This provides profile data for lower density plasmas, such as those anticipated during fast wave current drive experiments. Plans for a new CCD-based laser alignment system for position monitoring and feedback control will also be presented. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146326
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  • 8
    Electronic Resource
    Electronic Resource
    Determination of experimental tokamak plasma profiles using maximum-entropy analysis (1985)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 56 (1985), S. 984-986 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The diagnostician commonly faces the problem of extracting the maximum information on plasma spatial profiles from only a very limited and noisy data set. Conventionally, functional forms (e.g., a parabola raised to a power) are fitted to the measured data using nonlinear least-squares regression. This immediately biases the interpretation and constrains results to a narrow family of curves for which there may be no real evidence in the data. In this paper, we examine the consequences of abandoning this assumption and, instead, seek the constrained maximum entropy (ME) profile making no such assumptions. Results are compared with conventional analysis. The ME method has the inherent advantages of (i) yielding only positive (and therefore physically meaningful) profiles, (ii) suppression of noise on the data, and (iii) producing a profile which contains the least amount of spurious detail. The method is illustrated with reference to measured chord-average CO2 laser interferometer data taken on the Doublet III tokamak.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1138012
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  • 9
    Electronic Resource
    Electronic Resource
    γ-ray sources as comptonized X-ray sources (1982)
    [s.l.] : Nature Publishing Group
    Nature 297 (1982), S. 665-667 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Recently, several y-ray burst spectra have been measured with sufficient energy range and resolution to determine the continuum shape1. The continuum shape has usually been attributed to optically thin thermal bremsstrahlung, consistent with earlier results for the 1972 14 May burst2 and the Apollo ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/297665a0
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  • 10
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    Rapid Inward Impurity Transport during Impurity Pellet Injection on the DIII-D Tokamak (1998)
    American Physical Society
    Details
    Publication Date: 1998-11-16
    Print ISSN: 0031-9007
    Electronic ISSN: 1079-7114
    Topics: Physics
    Published by American Physical Society
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