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  • 1995-1999  (3)
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  • 1
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A photometrically calibrated polychromator utilizing layered synthetic microstructure coated flats (also known as multilayer mirrors, MLMs) as dispersive elements is operating on the Alcator C-Mod tokamak to measure the molybdenum emissions in the XUV. Molybdenum, the first wall material in C-Mod, is the dominant high Z impurity in the plasma. Three spectral regions are measured by three separate MLM-detector channels. The characteristic charge states in the region between 30–40 A(ring) are Mo xv to Mo xx, between 65–90 A(ring) are Mo xxiv to Mo xxvi, and between 110–130 A(ring) are Mo xxxi and Mo xxxii. The instrument's spectral resolution varies from 0.4 A(ring) at λ=30 A(ring) to 7 A(ring) at λ=130 A(ring). The temporal resolution is typically 1.0 ms, but sampling rates of less than 1 ms are possible. The instrument was photometrically calibrated at The Johns Hopkins University using a Manson soft x-ray light source. Power loss estimates from Mo xxiv to Mo xxvi, Mo xxxi, and Mo xxxii have been obtained during ohmic and ICRF plasmas using the mist transport code to model the molybdenum charge state distributions in the plasma. The Mo concentrations have also been determined. Mo contributes ∼0.1 to the Zeff of 1.3 during ohmic plasmas. This contribution increases during ICRF heating to ∼0.5 of the Zeff of 2. The polychromator functions as a time-resolved soft x-ray emission power loss monitor. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Impurity transport coefficients and the penetration efficiencies of intrinsic and injected impurities through the separatrix of diverted Alcator C-Mod discharges have been measured using x-ray and vacuum ultraviolet (VUV) spectroscopic diagnostics. The dominant low Z intrinsic impurity in C-Mod is carbon which is found to be present in concentrations of less than 0.5%. Molybdenum, from the plasma facing components, is the dominant high Z impurity and is typically found in concentrations of about 0.02%. Trace amounts of medium and high Z nonrecycling impurities can be injected at the midplane using the laser blow-off technique and calibrated amounts of recycling, gaseous impurities can be introduced through fast valves either at the midplane or at various locations in the divertor chamber. A five chord crystal x-ray spectrometer array with high spectral resolution is used to provide spatial profiles of high charge state impurities. An absolutely calibrated, grazing incidence VUV spectrograph with high time resolution and a broad spectral range allows for the simultaneous measurement of many impurity lines. Various filtered soft x-ray diode arrays allow for spatial reconstructions of plasma emissivity. The observed brightnesses and emissivities from a number of impurity lines are used together with the mist transport code and a collisional-radiative atomic physics model to determine charge state density profiles and impurity transport coefficients. Comparisons of the deduced impurity content with the measured Zeff and total radiated power of the plasma are made. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: X-ray spectra from Alcator C-Mod plasmas have been collected using a high wavelength resolution, five spectrometer array during a wide range of operating conditions, providing a large variety of diagnostic information. Each independently scannable von Hamos type spectrometer has a wavelength range of 2.8–4.0 A(ring), and the complete Rydberg series of helium- and hydrogenlike argon have been observed. Spectra of Δn=1 ground state transitions and satellites taken along different chords have been simulated using the results from a collisional-radiative model and the mist transport code. Line ratios are very sensitive to the electron temperature and deduced profiles are in good agreement with ECE profiles. Line intensities have been utilized to obtain absolute argon densities. The widths of the strongest lines have been used to deduce ion temperature profiles. Transitions from around n=9 to the ground state are populated by charge exchange in the outer regions of the plasma and these line intensities have been used to determine the neutral hydrogen density profile. Spectra from heliumlike scandium have been obtained during injection experiments and time histories and line intensities have been utilized to determine impurity transport coefficients. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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