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  • 1
    Electronic Resource
    Electronic Resource
    Benchmarking atomic physics models for magnetically confined fusion plasma physics experiments : 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. 375-378 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: In present magnetically confined fusion devices, high and intermediate Z impurities are either puffed into the plasma for divertor radiative cooling experiments or are sputtered from the high Z plasma facing armor. The beneficial cooling of the edge as well as the detrimental radiative losses from the core of these impurities can be properly understood only if the atomic physics used in the modeling of the cooling curves is very accurate. To this end, a comprehensive experimental and theoretical analysis of some relevant impurities is undertaken. Gases (Ne, Ar, Kr, and Xe) are puffed and nongases are introduced through laser ablation into the FTU tokamak plasma. The charge state distributions and total density of these impurities are determined from spatial scans of several photometrically calibrated vacuum ultraviolet and x-ray spectrographs (3–1600 Å), the multiple ionization state transport code transport code (MIST) and a collisional radiative model. The radiative power losses are measured with bolometery, and the emissivity profiles were measured by a visible bremsstrahlung array. The ionization balance, excitation physics, and the radiative cooling curves are computed from the Hebrew University Lawrence Livermore atomic code (HULLAC) and are benchmarked by these experiments. (Supported by U.S. DOE Grant No. DE-FG02-86ER53214 at JHU and Contract No. W-7405-ENG-48 at LLNL.) © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149410
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  • 2
    Electronic Resource
    Electronic Resource
    Diagnostics for local spectroscopic measurements in the divertor region of the Alcator C-Mod and DIII-D tokamaks : 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. 1047-1050 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Local measurements of line emission of either intrinsic or gas puffed impurities will be performed around and below the X point. Such spectroscopic measurements, together with divertor Thomson scattering and bolometric imaging will enable estimates of divertor impurity particle distributions and power losses. A proposed multilayer mirror (MLM) diagnostic mounted inside the tokamak vessel will measure XUV (100–200 Å) emission from impurities at multiple locations in the divertor region of the C-Mod tokamak. A prototype of this instrument measuring N V at 162.6 Å is scheduled to be installed on C-Mod with a single chordal view of the X point. A multichordal/multispectral device using MLMs and gratings has been designed for the DIII-D tokamak. The instrument will measure the resonance emission of C II to C VI from 40–2000 Å, thus enabling a more direct and reliable estimate of the impurity content in the divertor. At DIII-D, the device will be mounted on a port below the mid plane avoiding spectroscopic contamination from the core plasma. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147784
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  • 3
    Electronic Resource
    Electronic Resource
    How to beat the low resolution of multilayer mirror spectra (invited) : 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. 1002-1008 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The soft x-ray and extreme ultraviolet (XUV) impurity emissions from tokamaks (10 Å〈λ〈304 Å) have been extensively studied with high-resolution grazing incidence spectrographs, and atomic physics models predicting spectral line brightnesses have been benchmarked against these experimental data. This, together with the ability to perform large amounts of accurate atomic physics computations, enables the relaxation on the requirement for high resolution spectra. The multilayer mirror (MLM) is a low resolving power (λ/δ λ〈100) XUV dispersive/reflective optical element that obeys the Bragg law of reflection. MLM based monitors are compact, high-photon-throughput diagnostics capable of extracting XUV emissions of impurities from the harsh environment of large fusion reactor-type devices. We will show how atomic physics modeling can be used to extract the XUV spectral line brightnesses measured with low-resolution, high-photon-throughput, MLM-based devices. The Plasma Spectroscopy Group at The Johns Hopkins University has investigated the application of MLM based diagnostics for magnetically confined fusion plasmas: MLM based monitors have been constructed for and extensively used on DIII–D, Alcator C-Mod, TEXT, Phaedrus-T, and CDX-U to study the impurity behavior of elements ranging from He to Mo. Experiments were also performed in which MLMs were irradiated to a fast neutron fluence of 1.1×1019 n cm−2 at 270–300 °C, and the preliminary results indicate that MLMs would be a good first wall reflector for fusion plasmas. Future applications of MLM based devices to study divertor coolants (Ne, Ar, and Kr emissions) and "killer pellet" (W emissions) experiments will also be discussed. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147920
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  • 4
    Electronic Resource
    Electronic Resource
    Ultrasoft x-ray imaging system for the National Spherical Torus Experiment : 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. 572-576 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A spectrally resolved ultrasoft x-ray imaging system, consisting of arrays of high resolution (〈2 Å) and throughput (≥tens of kHz) miniature monochromators, and based on multilayer mirrors and absolute photodiodes, is being designed for the National Spherical Torus Experiment. Initially, three poloidal arrays of diodes filtered for C 1s-np emission will be implemented for fast tomographic imaging of the colder start-up plasmas. Later on, mirrors tuned to the C Lyα emission will be added in order to enable the arrays to "see" the periphery through the hot core and to study magnetohydrodynamic activity and impurity transport in this region. We also discuss possible core diagnostics, based on tomographic imaging of the Lyα emission from the plume of recombined, low Z impurity ions left by neutral beams or fueling pellets. The arrays can also be used for radiated power measurements and to map the distribution of high Z impurities injected for transport studies. The performance of the proposed system is illustrated with results from test channels on the CDX-U spherical torus at Princeton Plasma Physics Laboratory. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149272
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  • 5
    Electronic Resource
    Electronic Resource
    Far ultraviolet polychromator for spectroscopic characterization of the tokamak divertor and plasma scrape-off layer : 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. 340-343 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The Plasma Spectroscopy Group of The Johns Hopkins University is developing diagnostics for spectroscopic characterization of the tokamak plasma scrape-off layer and divertor regions. A far ultraviolet polychromator has been designed for radiative divertor studies at the Alcator C-Mod and D-IIID tokamaks. Local measurements of resonant transitions of lithium- to boron-like ions of intrinsic or seeded low Z impurity elements will be performed along multiple chords around the X point. Planar diffraction gratings and stacked grids will be used for dispersion and angular collimation of radiation. Phosphor wavelength converters coupled to a photomultiplier tube by an optical fiber will be used as detectors. The design provides a wavelength resolution of (similar, equals)10 Å, a spatial resolution of ≤2 cm, and an adequate photometric sensitivity. The in-vessel instrument, proposed for the Alcator C-Mod tokamak, will measure intensities of the lines at 1240 (N V), 765, 923 (N IV), and 990 Å (N III). The port-mounted polychromator at DIII-D will be able to monitor intensities of 1550 (C IV), 977, 1176 (C III), and 1335 Å (C II) lines. This, together with visible and bolometric diagnostics, should enable estimates of power losses, charge state distribution and local transport of the impurity ions in the divertor. A one-channel prototype of the C-Mod and D-IIID instruments is being built for the CDX-U spherical tokamak. Line-integrated brightnesses of the 2s–2p transition at 1550 Å will be measured and inverted to obtain C IV emissivity distribution. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149409
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  • 6
    Electronic Resource
    Electronic Resource
    An evaluation of multilayer mirrors for the soft x ray and extreme ultraviolet wavelength range that were irradiated with neutrons : 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. 757-760 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The Plasma Spectroscopy Group at the Johns Hopkins University develops high photon throughput multilayer mirror (MLM) based soft x ray and extreme ultraviolet (XUV 10 Å〈λ〈304 Å) spectroscopic diagnostics for magnetically confined fusion plasmas. The D-T reactions in large fusion reactor type devices such as the International Thermonuclear Experimental Reactor will produce neutrons at a rate as high as 5×1019 n s−1. The MLMs, which are used as dispersive and focusing optics, will not be shielded from these neutrons. In an effort to assess the potential radiation damage, four MLMs (No. 1: Mo/Si, d=87.8 Å, Zerodur substrate with 50 cm concave spherical curvature; No. 2: W/B4C, d=22.75 Å, Si wafer substrate; No. 3: W/C, d=25.3 Å, Si wafer substrate; and No. 4: Mo/Si, d=186.6 Å, Si wafer substrate) were irradiated with fast neutrons at the Los Alamos Spallation Radiation Effects Facility (LASREF). The neutron beam at LASREF has an energy distribution that peaks at 1–2 MeV with a tail that extends out to 100 MeV. The MLMs were irradiated to a fast neutron fluence of 1.1×1019 n cm−2 at 270–300 °C. A comparison between the dispersive and reflective characteristics of the irradiated MLMs and the corresponding qualities of control samples will be given. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1148449
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  • 7
    Electronic Resource
    Electronic Resource
    Compact collimated vacuum ultraviolet diagnostics for localized impurity measurements in fusion boundary plasmas (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 3270-3276 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Compact vacuum ultraviolet diagnostics for impurity emission measurements in boundary plasmas of nuclear fusion plasma devices are described. The instruments are designed for monitoring intensities of resonant impurity lines between 300 and 2000 Å. The intensities are used to infer basic yet important plasma parameters, such as density of impurity charge states, radiated power, or electron temperature and density estimates. All utilized components and materials satisfy ultrahigh vacuum and high bake-out temperature requirements, enabling the instruments to qualify for vacuum port or in-vessel placement, in close proximity to emitting plasmas. The instruments have high spatial (Δl≤1 cm) and temporal (Δτ≤100 μs) resolution. The spectral resolution is Δλ≤20 Å. Planar diffraction gratings at near-normal incidence are used for dispersion of incident radiation, collimated by high precision mechanical stacked grid collimators. Highly localized field of view, adequate throughput, and compactness distinguish these diagnostics from conventional slit instruments. A prototype monochromator for λ=1550 Å has been built, evaluated, radiometrically calibrated, and used on the CDX-U spherical torus for monitoring C IV emission in ohmic and high harmonic fast wave heated plasmas with Te(0)≤100 eV. An attractive mechanical collimator based Wadsworth mount spectrometer concept is presented and its application to impurity content and transport measurements in tokamaks is discussed. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1386906
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  • 8
    Electronic Resource
    Electronic Resource
    Ultrasoft x-ray telescopes for fluctuation imaging in fusion plasmas : 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. 732-736 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We present the design for a novel spectroscopic instrument for two-dimensional imaging of low-amplitude, fast fluctuations from magnetically confined fusion devices. The instrument is similar in principle to an ultrasoft x-ray (USXR) telescope recently developed for astrophysics application and uses a large (10–20-cm-diam), spherical multilayer mirror to select and concentrate a bright USXR impurity line (e.g., C VI Lyα at 33.7 Å, or C VI Hα at 182 Å), onto a low-noise fast, two-dimensional detector. A first version of the telescope will use a fast phosphor to convert the USXR image into visible light, which is then guided using fiber optics to a fast/gated charge-coupled-device camera outside the vacuum. Detailed signal-to-noise analysis indicates that, due to the high energy and brightness of the USXR line emission and large reflectivity of the present mirrors, such an instrument would allow imaging of subpercent amplitude fluctuations with ≤10 μs time resolution and sub-cm spatial resolution. At the same time, ray-tracing calculations show that a quite large plasma region (up to a few tens of cm extent) can be imaged. Another version of the telescope would use a two-dimensional array of extreme ultraviolet diodes at the focal plane, in which case fluctuations up to (approximate)0.1% could be imaged. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1318260
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  • 9
    Electronic Resource
    Electronic Resource
    Multilayer mirror and foil filter AXUV diode arrays on CDX-U spherical torus : 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. 737-741 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Recent upgrades to CDX-U spherical torus diagnostics include two 10-channel AXUV diode arrays. The multilayer mirror (MLM) array measures the λ150 O VI brightness profile in the poloidal plane using the Mo/B4C synthetic multilayer structures as dispersive elements. The foil filter array has a tangential view and is equipped with interchangeable clear aperture, beryllium and titanium filters. This allows measurements of radiated power, O VI or C V radial distributions, respectively. The O VI and C V emissivity and the radiated power profiles are highly peaked. A Neoclassical impurity accumulation mechanism is considered as an explanation. For radiated power measurements in the Te≤100 eV plasmas, photon energy dependent corrections must be used in order to account for nonlinear AXUV sensitivity in the range Ephot≤20 eV. The arrays are also used for characterization of resistive MHD phenomena, such as the low m modes, saw-tooth oscillations and internal reconnection events. Based on the successful operation of the diagnostics, a new ultra soft x-ray multilayer mirror diode AXUV diode array monitoring the 34 Å emissivity distribution of C VI will be built and installed on the National Spherical Torus Experiment. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1323254
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  • 10
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    Enhanced Energy Confinement and Performance in a Low-Recycling Tokamak (2006)
    American Physical Society
    Details
    Publication Date: 2006-08-17
    Print ISSN: 0031-9007
    Electronic ISSN: 1079-7114
    Topics: Physics
    Published by American Physical Society
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