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  • 1985-1989  (5)
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  • 1
    Electronic Resource
    Electronic Resource
    Poloidal rotation in Alcator C (1986)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 57 (1986), S. 2020-2022 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The poloidal rotation velocity in the edge region of ohmically heated Alcator C plasmas was measured using the Doppler shift of impurity emission lines. The measurements were made using a high-resolution, photon counting detector, sensitive to wavelengths from ∼1200 to ∼2000 A(ring), mounted in the exit plane of a 1-m Ebert–Fastie spectrometer. The transitions used were the 2s2p 1P01–2p2 1D2 at 1371.292 A(ring) in O v and 2s 2S1/2–2p 2P01/2 at 1242.804 A(ring) in N v, both of which exist near the limiter radius in Alcator C. The measured rotation velocity is ∼4.1×105 ±2.1×105 cm/s at n¯e∼1.7×1014 cm−3 in the direction of the electron diamagnetic drift and is ∼1.4×105 ±2.5×105 cm/s at n¯e∼2.3×1014 cm−3 in the ion diamagnetic drift direction, although the error bars associated with this last measurement do not preclude the possibility of zero rotation or rotation in the electron diamagnetic drift direction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1138777
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Measurement of the current density profile in the Alcator C tokamak using lithium pellets (1989)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 60 (1989), S. 3739-3743 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: High-speed lithium pellets have been injected into Alcator C tokamak plasmas in order to measure the internal magnetic field, and thus current density profiles. In the pellet ablation cloud, intense visible line radiation from the Li+ ion (λ≈5485 A(ring), 1s2s 3S−1s2p 3P) is polarized due to the Zeeman effect, and measurement of the polarization angle yields the direction of the total local magnetic field. A "snap shot'' of the q profile is obtained as the pellet penetrates from the edge into the center of the discharge, in a time of about 300 μs. The spatial resolution of the measurement is about 1 cm. At a toroidal field of BT=10 T, the emission in the unshifted π component of the Zeeman triplet is more than 80% polarized, and q profiles have been obtained. The pellets are perturbative (〈Δne〉/〈ne〉≈1), but the total pellet penetration time is at least a factor of 1000 smaller than the classical skin time. It can thus be anticipated that the current density profile should not be perturbed significantly during the time of the measurement. With some relatively straightforward modifications and refinements, precision approaching 10% for the measurement of q profiles should be achievable. The technique appears viable, using Li, as long as the toroidal field is (approximately-greater-than)4 T.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1140485
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    High spectral resolution, photon counting detector for Doppler temperature measurements in magnetically confined plasmas (1987)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 58 (1987), S. 520-529 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: This paper describes the design, construction, and performance of a single-stage microchannel-plate image intensifier used as a photon counting detector over the wavelength range from 1150 to ∼2000 A(ring). The intensifer incorporates three high strip current (∼300 μA) microchannel plates, constructed with 12-μ-diam channels and 15-μ center–center spacing, in a "Z'' configuration. The use of high strip current MCPs requires gating the power supply to protect the plates from thermal runaway of the strip current. The output pulses are proximity focused onto a P-46 phosphor screen, which is fiber-optically coupled to a linear, self-scanning photodiode array. Maximum frame rates for the photodiode array are ∼ 125 000 frames/s, with maximum count rates of ∼25 000 photoevents/s. The detector was placed at the focal plane of a 1-m focal length Ebert–Fastie spectrometer and the performance characteristics of the spectrometer-detector system were evaluated using a hollow cathode Pt lamp. The linewidths measured during this evaluation demonstrate that the spatial resolution of the detector is better than 50 μ. The spectrometer-detector system was then used to determine ion temperatures from Doppler broadened impurity lines emitted from plasmas of the Alcator C tokamak. This detector demonstrated more than an order of magnitude increase in sensitivity compared to a photon-counting photomultiplier tube with a vibrating mirror previously used for these measurements with the same spectrometer. This permitted a determination of the central ion temperature of the Alcator C tokamak using the "forbidden'' line of Fe xii at 1354.1 A(ring) which was not detected with the previous system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1139263
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Observations of centrally peaked impurity profiles following pellet injection in the Alcator-C tokamak (1986)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 57 (1986), S. 2195-2195 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Differently filtered x-ray arrays have been used to instantaneously measure central carbon and molybdenum profiles, Alcator's dominant light and heavy impurities, following pellet injection. Approximately 40 ms after the pellet, the width of the carbon profile was close to the neoclassical prediction of a source-free equilibrium state. (Carbon is a plateau impurity.) The experimental molybdenum profile, which is more uncertain, was between a factor of 1.3 and 3.0 that of the asymptotic prediction of neoclassical theory. Carbon, the dominant nonhydrogenic contributor to Zeff, was found to dramatically affect sawtooth dynamics by altering the central resistivity. Specifically, following injection of the pellet the carbon profile became progressively more peaked, the effect of which was to lengthen the sawtooth period. Approximately 40 ms after the pellet, an internal disruption occurred which reduced on-axis carbon and molybdenum by a factor of 3. (In comparison, the corresponding temperature drop was only about 10%.) After this internal disruption, the sawtooth period shortened as a consequence of carbon not dramatically repeaking. The instrumentation, as well as the plasma conditions needed to make such measurements, will be described. Details of this work are contained in the report PFC/JA-85-41. This work was supported in part by the U.S. DOE Contract No. DE-AC02-78ET51013.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1138729
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    Evaluation of a photon-counting detector for Doppler ion temperature measurements (abstract) (1985)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 56 (1985), S. 870-870 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A photon-counting detector for determination of the ion temperature in magnetically confined plasmas has been developed.1 The detector is based around an image intensifier tube which is fiber optically coupled to a self-scanning linear photodiode array. The image intensifier incorporates three high strip current (∼280 μA) microchannel plates in a "Z'' configuration. Frame times of 10 μs are possible through the use of pixel selection, resulting in a time resolution on the order of 5 ms. The detector system will be mounted on a 1-M Ebert–Fastie spectrometer and used to study the Alcator C plasma. Laboratory evaluation of the detector and associated electronics has been completed. The results of this evaluation, and progress toward integration of the detector and spectrometer systems, will be presented. This work, and additional information, will be published in greater detail in the near future.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1138081
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    Paper (German National Licenses)
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