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  • 1
    Electronic Resource
    Electronic Resource
    Calibration of grazing incidence spectrometers using charge transfer excitation (abstract) (1985)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 56 (1985), S. 868-868 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The sequence of radiative cascades following charge transfer between energetic neutral atoms and C6+, N7+, and O8+ are readily observed in high-temperature plasma devices where the field of view of a vacuum spectrometer includes a neutral heating beam. These charge exchange excited (CXE) lines have well defined relative intensities that are not strongly dependent on the theory used to compute the primary excitation.1 They have been exploited in the ISX-B tokamak as an in situ method of measuring the relative response of a grazing incidence spectrometer from 102 to 1164 A(ring). Mixing of energy levels by external fields or by collisions are shown to have little effect on treating l as a good quantum number when computing the ratios of effective emission cross sections.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1138076
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  • 2
    Electronic Resource
    Electronic Resource
    Radiative divertor plasmas with convection in DIII-D : The 39th annual meeting of division of plasma physics of APS (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 1736-1743 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The radiation of divertor heat flux on DIII-D [J. Luxon et al., in Proceedings of the 11th International Conference on Plasma Physics and Controlled Nuclear Fusion (International Atomic Energy Agency, Vienna, 1987), p. 159] is shown to greatly exceed the limits imposed by assumptions of energy transport dominated by electron thermal conduction parallel to the magnetic field. Approximately 90% of the power flowing into the divertor is dissipated through low-Z radiation and plasma recombination. The dissipation is made possible by an extended region of low electron temperature in the divertor. A one-dimensional analysis of the parallel heat flux finds that the electron temperature profile is incompatible with conduction-dominated parallel transport. Plasma flow at up to the ion acoustic speed, produced by upstream ionization, can account for the parallel heat flux. Modeling with the two-dimensional fluid code UEDGE [T. Rognlien, J. L. Milovich, M. E. Rensink, and G. D. Porter, J. Nucl. Mater. 196–198, 347 (1992)] has reproduced many of the observed experimental features. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872842
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  • 3
    Electronic Resource
    Electronic Resource
    Signatures of deuterium recombination in the DIII-D divertor (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2989-2996 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thomson scattering measurements performed in the divertor of the DIII-D tokamak [Plasma Physics Controlled Nuclear Fusion Research, 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. I, p. 159] during detached operation show that the electron temperatures are typically between 0.8 and 2.0 eV throughout a region which may extend several centimeters above the target plate. At such low temperatures the excitation of recycling deuterium atoms or impurities should be weak. Nevertheless, significant radiation is frequently detected in these locations. It has been suggested that recombination processes, which become important only below about 1.5 eV for deuterium, are responsible for the observed emission. This hypothesis has been investigated by comparing ratios of deuterium lines from attached and detached plasmas with theoretical ratios expected for ionizing or recombining conditions. The analysis of several discharges indicates that the mechanism for production of the emission changes from being collisional excitation of atomic deuterium to a mixture of collisional-radiative recombination and collisional excitation as plasmas evolve from attached to detached states. Localization of D-α emission to low-temperature regions using tangentially viewing camera data together with Thomson scattering results and measurements of deuterium atom temperatures are consistent with these conclusions. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872432
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  • 4
    Electronic Resource
    Electronic Resource
    The two-dimensional structure of radiative divertor plasmas in the DIII-D tokamak : The 38th annual meeting of the Division of Plasma Physics (DPP) of the American Physical Society (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1761-1773 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Recent measurements of the two-dimensional (2-D) spatial profiles of divertor plasma density, temperature, and emissivity in the DIII-D tokamak [J. Luxon et al., in Proceedings of the 11th International Conference on Plasma Physics and Controlled Nuclear Fusion (International Atomic Energy Agency, Vienna, 1987), p. 159] under highly radiating conditions are presented. Data are obtained using a divertor Thomson scattering system and other diagnostics optimized for measuring the high electron densities and low temperatures in these detached divertor plasmas (ne≤1021 m−3, 0.5 eV≤Te). D2 gas injection in the divertor increases the plasma radiation and lowers Te to less than 2 eV in most of the divertor volume. Modeling shows that this temperature is low enough to allow ion–neutral collisions, charge exchange, and volume recombination to play significant roles in reducing the plasma pressure along the magnetic separatrix by a factor of 3–5, consistent with the measurements. Absolutely calibrated vacuum ultraviolet spectroscopy and 2-D images of impurity emission show that carbon radiation near the X-point, and deuterium radiation near the target plates contribute to the reduction in Te. Uniformity of radiated power (Prad) (within a factor of 2) along the outer divertor leg, with peak heat flux on the divertor target reduced fourfold, was obtained. A comparison with 2-D fluid simulations shows good agreement when physical sputtering and an ad hoc chemical sputtering source (0.5%) from the private flux region surface are used. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872278
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  • 5
    Electronic Resource
    Electronic Resource
    Spectroscopic characterization of the DIII-D divertor (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 355-368 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Radiative losses along a fixed view into the divertor chamber of the DIII-D tokamak [Plasma Physics Controlled Nuclear Fusion Research 1986 (International Atomic Energy Agency, Vienna, 1987), Vol I, p. 159] have been characterized for attached and partially detached discharges by analyzing line-integrated vacuum ultraviolet (VUV) signals. Essentially all the emission can be ascribed to carbon and deuterium. Because the majority of the most intense lines, which lie at wavelengths above 1100 Å, are not accessible to the present instrumentation, extensive use has been made of collisional-radiative (CR) calculations for level populations of the important ions in order to relate the total radiated power to shorter wavelength transitions. In beam-heated plasmas, the fraction of radiation detected from carbon along the VUV spectrometer view is usually between 50% and 80% of the total. Carbon densities are estimated from a simplified approach to modelling the emission using a one-dimensional transport code. For partially detached plasmas the concentrations range from 2%–6% of the electron density; but in attached plasmas it appears that carbon may supply most of the electrons in the divertor region just below the X point. Ion temperatures are measured from Doppler broadening of spectral lines by fitting measured profiles to theoretical lineshapes, which account precisely for atomic sublevel splitting caused by the Zeeman/Paschen-Back effect in the tokamak magnetic field. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872095
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  • 6
    Electronic Resource
    Electronic Resource
    Carbon flows in attached divertor plasmas : 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. 1837-1842 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Parallel flow velocities of carbon ions in the DIII-D divertor [J. Luxon et al., Plasma Physics Controlled Nuclear Fusion Research, 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. I, p. 159; S. L. Allen et al., Controlled Fusion and Plasma Physics, 1987 (Proc. 24th European Conf. Berchtesgaden, 1997), Vol. 21 A, Part III, p. 1129] have been studied under various operating conditions: L-mode (low-confinement mode), H-mode (high-confinement mode) with low-frequency ELMs (edge-localized modes), and H-mode with high-frequency ELMs. Both normal and reversed flows (toward the target plate and away from the target plate, respectively) are observed under all conditions, with the reversed speeds being as much as a factor of four greater than normal speeds. Magnitudes are approximately the same for L-mode and H-mode operation with high-frequency ELMs. In H-mode conditions with low-frequency ELMs, normal velocities are frequently observed to decline while reversed velocities increase in comparison to the other two conditions. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873442
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  • 7
    Electronic Resource
    Electronic Resource
    Drift-wave-like density fluctuations in the Advanced Toroidal Facility (ATF) torsatron (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 398-413 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Density fluctuations in low-collisionality, low-beta (β∼0.1%), currentless plasmas produced with electron cyclotron heating (ECH) in the Advanced Toroidal Facility (ATF) torsatron [Fusion Technol. 10, 179 (1986)] have been studied using a 2 mm microwave scattering diagnostic. Pulsed gas puffing is used to produce transient steepening of the density profile from its typically flat shape; this leads to growth in the density fluctuations when the temperature and density gradients both point in the same direction in the confinement region. The wave number spectra of the fluctuations that appear during this perturbation have a maximum at higher k⊥ρs (∼1) than is typically seen in tokamaks. The in–out asymmetry of the fluctuations along the major radius correlates with the distribution of confined trapped particles expected for the ATF magnetic field geometry. During the perturbation, the relative level of the density fluctuations in the confinement region (integrated over normalized minor radii ρ from 0.5 to 0.85) increases from ñ/n∼1% when the density profile is flat to ñ/n∼3% when the density profile is steepened. These observations are in qualitative agreement with theoretical expectations for helical dissipative trapped-electron modes (DTEMs), which are drift-wave instabilities associated with particle trapping in the helical stellarator field; they suggest that trapped-electron instabilities may play a role in constraining the shape of the density profile in ATF, but have little effect on global energy confinement. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870966
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  • 8
    Electronic Resource
    Electronic Resource
    Spectroscopic analysis of normal and reversed ion flows in the DIII-D divertor (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 541-549 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Flow velocities of C+, C2+, B+, and D+ parallel to the magnetic field in the DIII-D [J. Luxon, P. Anderson, F. Batty et al., Plasma Physics Controlled Nuclear Fusion Research, Proceedings of the 11th International Conference, Tokyo, 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. I, p. 159] divertor have been measured from Doppler shifts of spectral lines. In general, both normal flows (toward the target plate) and reversed flows (away from the target plate) are observed in the outer scrape-off layer with the reversed flows occurring near the separatrix. Following the transition from attached to partially detached conditions, normal flow velocities generally speed up while in some regions reversed flows are observed to slow down. In high density plasmas, deuteron velocities are reflected in Balmer line emission which originates mainly from atoms which have thermalized by charge exchange or which have been formed by recombination. Low-temperature areas of nearly stagnated deuteron flow have been observed. In these regions recombination should be efficient for neutralizing the divertor plasma. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873198
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  • 9
    Electronic Resource
    Electronic Resource
    Effects of magnetic geometry, fluctuations, and electric fields on confinement in the Advanced Toroidal Facility (1992)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 4 (1992), S. 2104-2110 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Recent experiments in the Advanced Toroidal Facility (ATF) [Fusion Technol. 10, 179 (1986)] have been directed toward investigations of the basic physics mechanisms that control confinement in this device. Measurements of the density fluctuations throughout the plasma volume have provided indications for the existence of theoretically predicted dissipative trapped electron and resistive interchange instabilities. These identifications are supported by results of dynamic configuration scans of the magnetic fields during which the magnetic well volume, shear, and fraction of confined trapped particles are changed continuously. The influence of magnetic islands on the global confinement has been studied by deliberately applying error fields which strongly perturb the nested flux-surface geometry, and the effects of electric fields have been investigated by means of biased limiter experiments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860018
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  • 10
    Electronic Resource
    Electronic Resource
    Second stability in the ATF torsatron—Experiment and theory (1990)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 2 (1990), S. 1353-1358 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Access to the magnetohydrodynamic (MHD) second stability regime has been achieved in the Advanced Toroidal Facility (ATF) torsatron [Fusion Technol. 10, 179 (1986)]. Operation with a field error that reduced the plasma radius and edge rotational transform resulted in peaked pressure profiles and increased Shafranov shift that lowered the theoretical transition to ideal MHD second stability to β0≈1.3%; the experimental β values (β0≤3%) are well above this transition. The measured magnetic fluctuations decrease with increasing β, and the pressure profile broadens, consistent with the theoretical expectations for self-stabilization of resistive interchange modes. Initial results from experiments with the field error removed show that the pressure profile is now broader. These later discharges are characterized by a transition to improved (×2–3) confinement and a marked change in the edge density fluctuation spectrum, but the causal relationship of these changes is not yet clear.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859555
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