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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
    Toroidal and poloidal soft x-ray imaging system on the DIII-D tokamak (1988)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 59 (1988), S. 1807-1809 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A toroidal soft x-ray imaging system is being added to the currently installed poloidal soft x-ray system on the DIII-D tokamak. The poloidal array is used to determine the poloidal mode structure and location of internal helical MHD perturbations in the plasma. The new array will add toroidal mode identification capability. The four detector arrays are toroidally spaced in a manner that allows identification of toroidal mode numbers up to 24. Beryllium vacuum windows separate the detectors from the tokamak vacuum and also serve as low-energy filters. The separate detector vacuum chambers can be filled with a gas that changes the low-energy cutoff of the system. By proper selection of the gas and pressure the low-energy cutoff can be chosen over the entire range of the detector sensitivity (500–1200 eV). This capability can be used to produce crude x-ray spectra for the entire imaging system or for gain control.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1140119
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  • 3
    Electronic Resource
    Electronic Resource
    Vacuum ultraviolet and ultrasoft x-ray diode detectors for tokamak plasmas (1988)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 59 (1988), S. 883-888 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Ultrasoft x-ray diode (USXRD) arrays have been used on DIII-D and ASDEX to study plasma edge radiation, in the photon energy range from 10 eV to 10 keV. The detectors are extremely useful and versatile due to their simplicity and compactness. Furthermore, absolute quantum efficiencies (QE) of many photocathodes such as vitreous C, Al, Cu, CuI, CsI, and Au have been measured in recent years. With filter technique, broadband resolution, E/ΔE∼1, is possible. Quantum-efficiency comparison of USXRD with semiconductor XRD is also presented to better understand the regions of applicability for each detector.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1139798
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  • 4
    Electronic Resource
    Electronic Resource
    Investigation of physical processes limiting plasma density in high confinement mode discharges on DIII-D : 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. 1752-1760 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A series of experiments was conducted on the DIII-D tokamak [J. L. Luxon and L. G. Davis, Fusion Technol. 8, 441 (1985)] to investigate the physical processes which limit density in high confinement mode (H-mode) discharges. The typical H-mode to low confinement mode (L-mode) transition limit at high density near the empirical Greenwald density limit [M. Greenwald et al., Nucl. Fusion 28, 2199 (1988)] was avoided by divertor pumping, which reduced divertor neutral pressure and prevented formation of a high density, intense radiation zone (MARFE) near the X-point. It was determined that the density decay time after pellet injection was independent of density relative to the Greenwald limit and increased nonlinearly with the plasma current. Magnetohydrodynamic (MHD) activity in pellet-fueled plasmas was observed at all power levels, and often caused unacceptable confinement degradation, except when the neutral beam injected (NBI) power was ≤3 MW. Formation of MARFEs on closed field lines was avoided with low safety factor (q) operation but was observed at high q, qualitatively consistent with theory. By using pellet fueling and optimizing discharge parameters to avoid each of these limits, an operational space was accessed in which density ∼1.5×Greenwald limit was achieved for 600 ms, and good H-mode confinement was maintained for 300 ms of the density flat-top. More significantly, the density was successfully increased to the limit where a central radiative collapse was observed, the most fundamental density limit in tokamaks. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872277
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  • 5
    Electronic Resource
    Electronic Resource
    Wall stabilization of high beta plasmas in DIII-D (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 2390-2396 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Detailed analysis of recent high beta discharges in the DIII-D [Plasma Physics Controlled Nuclear Fusion Research, 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. I, p. 159] tokamak demonstrates that the resistive vacuum vessel can provide stabilization of low n magnetohydrodynamic (MHD) modes. The experimental beta values reaching up to βT=12.6% are more than 30% larger than the maximum stable beta calculated with no wall stabilization. Plasma rotation is essential for stabilization. When the plasma rotation slows sufficiently, unstable modes with the characteristics of the predicted "resistive wall'' mode are observed. Through slowing of the plasma rotation between the q=2 and q=3 surfaces with the application of a nonaxisymmetric field, it has been determined that the rotation at the outer rational surfaces is most important, and that the critical rotation frequency is of the order of Ω/2π=1 kHz. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871262
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  • 6
    Electronic Resource
    Electronic Resource
    Results of counterneutral beam injection on the DIII-D tokamak (1989)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 1 (1989), S. 1843-1849 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Limiter, single-null, and double-null divertor plasmas have been heated by hydrogen neutral beam injection in the direction opposite to that of the plasma current. The H-mode power threshold is reduced by approximately 25% for counterinjection. Sawtooth suppression was possible only for high neutral beam power and for high values of the safety factor. No confinement improvement over similar coinjection discharges was observed in H-mode, L-mode, or limiter discharges. In plasmas without sawteeth, metallic impurity buildup in the central region of the plasma eventually leads to a reduction in confinement. The parametric dependence of energy confinement for both L-and H-mode plasmas was found to behave in the same manner during similar coinjection experiments. H-mode confinement increased linearly with increasing plasma current (65 msec/MA at 9 MW). Both L-mode and H-mode energy confinement decreased with increasing neutral beam power. At 1.25 MA, the L-mode plasmas had a confinement time that was less than that predicted by Kaye–Goldston scaling.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859209
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  • 7
    Electronic Resource
    Electronic Resource
    Modification of sawteeth by second harmonic electron-cyclotron heating in a tokamak (1989)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 1 (1989), S. 404-413 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electron-cyclotron heating, using second harmonic waves launched from the low field side, has a strong effect on sawteeth in the DIII-D tokamak [Plasma Physics and Controlled Nuclear Fusion Research, 1986 (IAEA, Vienna, 1987), Vol. I, p. 159]. There are two distinct methods and mechanisms for sawtooth period extension. In the first case a factor of 6 increase in sawtooth period, compared to that during Ohmic heating, occurs with electron-cyclotron heating (ECH) localized near the q=1 surface. The sawtooth period increases faster than linearly with increasing ECH power. Qualitatively, there is agreement with sawtooth suppression models, although details of the accompanying m/n=1/1 oscillation appear inconsistent. The second case is a technique for complete sawtooth suppression in which impurities and off-axis heating broaden the current profile and drive q0〉1. It appears that the temperature and the current and q profiles inside q=1 are determined by the magnetohydrodynamic activity, which is modified by ECH, and not by the ECH power deposition directly.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859154
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  • 8
    Electronic Resource
    Electronic Resource
    Electron cyclotron heating correlation with tokamak toroidal plasma rotation (1988)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 31 (1988), S. 687-691 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Toroidal rotation of the central plasma core has been observed prior to and during electron cyclotron heating (ECH) in the Doublet III tokamak [in Plasma Physics and Controlled Nuclear Fusion Research 1984, Proceedings of the Tenth International Conference, London (IAEA, Vienna, 1985), Vol. 1, p. 131]. Measurements were made using a curved-crystal Bragg x-ray spectrometer with spectral resolution of λ/Δλ of greater than 19 000 and temporal resolution of 20 msec. Ion rotation velocity was determined from the Doppler shift of x rays emitted from the plasma impurity Ti XXI resonance line. Ion temperatures were determined from the Doppler broadening of this line. A study of purely Ohmic discharges suggests that nonrotating discharges exhibit magnetohydrodynamic activity other than sawtooth oscillations, while those that rotate exhibit sawteeth. Discharges with plasma rotation prior to the appliction of ECH appear to heat more effectively than those that do not. Velocity and temperature histories show that there are temporal characteristics corresponding to whether the plasma was or was not effectively heated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.866800
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  • 9
    Electronic Resource
    Electronic Resource
    Prospects for charge-exchange-recombination-based measurements on International Thermonuclear Experimental Reactor using a helium diagnostic neutral beam : 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. 886-889 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Several important measurements in the International Thermonuclear Experimental Reactor (ITER) diagnostic mission, including the primary one of core helium ash density, are expected to be addressed using active spectroscopic techniques. These methods rely on the use of a dedicated diagnostic neutral beam (DNB) which has been optimized for the dual requirements of beam penetration and charge exchange cross section. For hydrogenic beams, this results in an optimal beam energy of ∼100 keV/amu. Signal-to-noise estimates using realistic geometries and the existing ITER profile and equilibrium data have confirmed the stringent requirements on beam quality and intensity to satisfy the stated ITER measurement precisions. In this article we consider the use of a neutral helium DNB for making active spectroscopic measurements on ITER, since helium beams offer better penetration in dense plasma for a given energy, and the prospects for given source performance may also be improved. Drawbacks include the more difficult absolute calibration of the beam density profile as well as the fundamental problem of uniquely identifying the source (fusion-based ash, beam core fuelling, or edge DNB neutralizer/source efflux) of the observed He charge-exchange recombination line in order to unambiguously characterize core helium buildup and confinement on ITER. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149408
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  • 10
    Electronic Resource
    Electronic Resource
    Plasma mass density, species mix, and fluctuation diagnostics using a fast Alfvén wave : 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. 478-479 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We propose use of a fast Alfvén wave interferometer and reflectometer as a tokamak diagnostic to measure the plasma mass density, D–T species mix profile, and density fluctuations. Utilizing the property that the phase velocity of the fast wave propagating across the magnetic field is the Alfvén speed with thermal correction, this fast wave interferometer on the DIII-D tokamak was successfully used to obtain the line integrated density. Since the position of the ion–ion hybrid cutoff in tokamaks is uniquely determined by the species mix ratio and wave frequency, the reflectometer arrangement finds the species mix profile. The inversion method of reflectometry is discussed. The multiple chord interferometer also measures the mass density fluctuation profile. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147610
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