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  • Electronic Resource  (16)
  • 1995-1999  (7)
  • 1985-1989  (8)
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  • Electronic Resource  (16)
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  • 1
    Electronic Resource
    Electronic Resource
    Experimental constraints on transport from dimensionless parameter scaling studies : 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. 1695-1702 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The scalings of heat transport with safety factor (q), normalized collisionality (ν), plasma beta (β), and relative gyroradius (ρ*) have been measured on the DIII-D tokamak [Fusion Technol. 8, 441 (1985)]. The measured ρ*, β and ν scalings of heat transport indicate that E×B transport from drift wave turbulence is a plausible basis for anomalous transport. For high confinement (H) mode plasmas where the safety factor was varied at fixed magnetic shear, the effective (or one-fluid) thermal diffusivity was found to scale like χeff∝q2.3±0.64 , with the ion and electron fluids having the same q scaling to within the experimental errors except near the plasma edge. The scaling of the thermal confinement time with safety factor was in good agreement with this local transport dependence, τth∝q−2.42±0.31 ; however, when the magnetic shear was allowed to vary to keep q0 fixed during the (edge) safety factor scan, a weaker global dependence was observed, τth∝q95−1.43±0.23. This weaker dependence was mainly due to the change in the local value of q between the two types of scans. The combined ρ*, β , ν and q scalings of heat transport for H-mode plasmas on DIII-D reproduce the empirical confinement scaling using physical (dimensional) parameters with the exception of weaker power degradation. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872838
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  • 2
    Electronic Resource
    Electronic Resource
    Erratum: "Role of the radial electric field in the transition from L (low) mode to H (high) mode to VH (very high) mode in the DIII-D tokamak'' [Phys. Plasmas 1, 1536 (1994)] (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 1358-1358 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871492
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  • 3
    Electronic Resource
    Electronic Resource
    Beyond paradigm: Turbulence, transport, and the origin of the radial electric field in low to high confinement mode transitions in the DIII-D tokamak (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 2397-2407 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The paradigm of shear suppression of turbulence as the mechanism for the low to high confinement mode (L to H) transition is examined by quantitative comparison of the predictions of the paradigm with experimental results from the DIII-D tokamak [Plasma Physics and Controlled Fusion Research (International Atomic Energy Agency, Vienna, 1986), p. 159]. The L to H transition trigger is V×B rotation, not the main ion pressure gradient. The radial electric field Er shear increases before the fluctuation suppression, consistent with increasing Er shear as the cause of the turbulence suppression. The spatial dependence of the turbulence reduction is consistent with shear suppression for negative Er shear. For positive Er shear, the turbulence suppression is consistent with the effect of Er curvature for modes for which an Er well is destabilizing. Finally, the transport barrier depends on the phase angle between the density and potential fluctuations inside the Er well, an effect not included in existing L to H transition models. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871263
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  • 4
    Electronic Resource
    Electronic Resource
    A fast charge coupled device detector for charge exchange recombination spectroscopy on the DIII-D Tokamak (abstract) : 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. 1019-1019 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Charge exchange recombination (CER) spectroscopy has become a standard diagnostic for Tokamaks. CER measurements have been used to determine spatially and temporally resolved ion temperature, toroidal and poloidal ion rotation speed, impurity density, and radial electric field. Knowledge of the spatial profile and temporal evolution of the electric field shear in the plasma edge is crucial to understanding the physics of the L to H transition. High speed CER measurements are also valuable for edge localized mode studies. Since the 0.52 ms minimum time resolution of our present system is barely adequate to study the time evolution of these phenomena, we have developed a new charge coupled device (CCD) detector system with about a factor of 2 better time resolution. In addition, our existing system detects sufficient photons to utilize the shortest time resolution only under exceptional conditions. The new CCD detector has a quantum efficiency of about 0.65, which is a factor of 7 better than our previous image intensifier-silicon photodiode detector systems. We have also equipped the new system with spectrometers of lower f/number. This combination should allow more routine operation at the minimum integration time, as well as improving data quality for measurements in the divertor-relevant region outside of the separatrix. Construction details, benchmark data, and initial Tokamak measurements for the new system will be presented. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147825
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  • 5
    Electronic Resource
    Electronic Resource
    Triton confinement and energy-loss studies with a time-resolved neutron detector (abstract) (1985)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 56 (1985), S. 1126-1126 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The expected results are presented for a fast, selective 14-MeV neutron detector which should be capable of separately measuring the confinement and energy loss of fast tritons for the first time. The tritons, from D–D reactions in a deuterium plasma, are observed when they collide with deuterons while slowing down, producing a characteristic 14-MeV neutron. Triton experiments are an excellent test for the confinement of fusion-produced alphas in a self-sustained reactor, which is critically dependent on plasma heating by the alphas. The triton production rate is pulsed by injecting a burst of deuterium using a neutral-beam heating source. The temporal distribution of the 14-MeV neutron flux is determined by the confinement and slowdown rate of the tritons. The expected flux is calculated as a function of time for the predicted triton transport, anomalous particle losses, and anomalous energy-loss rates, thus demonstrating how the various effects can be separately determined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1138191
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  • 6
    Electronic Resource
    Electronic Resource
    Poloidal magnetic field measurements on TEXT using the Zeeman current profile diagnostic (abstract) (1985)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 56 (1985), S. 1071-1071 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The Zeeman current-density profile diagnostic system installed on TEXT has observed the polarization shift of the π-line of the Zeeman split Li D lines due to the poloidal magnetic fields. The Li is injected into the plasma as a 95-keV neutral beam, and a cw dye laser is used to measure polarization shifts. The laser is tuned into resonance with the π-line and the polarization vector of the laser is rotated at 50-kHz using an electro-optic technique. The resulting 100-kHz laser-induced fluorescence signal is phase analyzed in order to observe the polarization shifts due to poloidal field. The Li beam intensity into the tokamak is approximately 1 mA and the dye laser intensity is 1 W at 3 GHz bandwidth. The diagnostic system and these early results will be discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1138225
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  • 7
    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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  • 8
    Electronic Resource
    Electronic Resource
    A fast charge coupled device detector for charge exchange recombination spectroscopy on the DIII-D Tokamak (1997)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 1233-1237 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Charge exchange recombination (CER) spectroscopy has become a standard diagnostic for Tokamaks. CER measurements have been used to determine spatially and temporally resolved ion temperature, toroidal and poloidal ion rotation speed, impurity density, and radial electric field. Knowledge of the spatial profile and temporal evolution of the electric field shear in the plasma edge is crucial to understanding the physics of the L to H transition. High speed CER measurements are also valuable for edge localized mode studies. Since the 0.52 ms minimum time resolution of our present system is barely adequate to study the time evolution of these phenomena, we have developed a new charge coupled device (CCD) detector system with about a factor of 2 better time resolution. In addition, our existing system detects sufficient photons to utilize the shortest time resolution only under exceptional conditions. The new CCD detector has a quantum efficiency of about 0.65, which is a factor of 7 better than our previous image intensifier-silicon photodiode detector systems. We have also equipped the new system with spectrometers of lower f/number. This combination should allow more routine operation at the minimum integration time, as well as improving data quality for measurements in the divertor-relevant region outside of the separatrix. Construction details, benchmark data, and initial Tokamak measurements for the new system will be presented. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147895
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  • 9
    Electronic Resource
    Electronic Resource
    Development of lithium beam emission spectroscopy as an edge fluctuation diagnostic for DIII-D (invited) : Proceedings of the tenth topical conference on high temperature plasma diagnostics (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 806-811 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: As part of the DIII-D diagnostic complement designed to address L–H transition physics issues, we have developed and commissioned a diagnostic neutral lithium beam and multichannel fluorescence detection system to investigate the edge plasma density and its associated fluctuations. The use of lithium offers several advantages for tokamak edge beam emission spectroscopy studies, including large excitation cross sections which are relatively insensitive to temperature variation, the availability of the 670.8 nm resonance line well separated from most plasma line emission, and the suitability of modest beam energies and currents to probe even dense H-mode plasmas. These features permit measurements of collisionally induced fluctuations to be obtained with good spatial (〈1 cm) and temporal (〈10 μs) resolution. The improvements over previous lithium beam diagnostics which were required to successfully make these measurements in a large, remotely controlled machine environment will be discussed, along with the present state of the diagnostic system and our plans for future improvements of this technique. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146227
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  • 10
    Electronic Resource
    Electronic Resource
    Low-divergence, high-brightness lithium ion source for plasma diagnostics (1988)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 59 (1988), S. 1735-1737 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Plasma diagnostics employing energetic lithium beams are in routine use on several present-day tokamak experiments. These measurements are constrained by the availability of a suitable lithium ion source. Necessary and/or desirable parameters include narrow energy spread, high-emission current density, simplicity, and long lifetime. The existing ion gun on the TEXT experiment uses the thermionic emitter β-eucryptite and meets the above requirements, except for being limited to a useful emission of about 4 mA. We will present design criteria and accelerator results for a new ion gun capable of 15-mA emission based on an increased emitter area. Important design considerations are the thermal and mechanical properties of the large (∼20 cm2) emitter area and the ion optics required to focus the emitted flux into a beam of ∼1-cm2 cross section. The potential improvement in the performance of both the TEXT and ASDEX diagnostic systems will be discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1140095
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