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  • 2020-2022  (2)
  • 1990-1994  (41)
  • 1
    Electronic Resource
    Electronic Resource
    Midplane Faraday rotation: A densitometer for large tokamaks : Proceedings of the 9th topical conference on high temperature plasma diagnostics (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 5154-5156 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The density in a large tokamak such as International Thermonuclear Experimental Reactor (ITER), or any of the proposed future US machines, can be determined by measuring the Faraday rotation of a 10.6 μm laser directed tangent to the toroidal field. If there is a horizontal array of such beams, then ne(R) can be readily obtained with a simple Abel inversion about the center line of the tokamak. For a large machine, operated at a full field of 30 T m and a density of 2×1020/m3, the rotation angle would be quite large−about 60° for two passes. A layout in which a single laser beam is fanned out in the horizontal midplane of the tokamak, with a set of retroreflectors on the far side of the vacuum vessel, would provide good spatial resolution, depending only upon the number of reflectors. With this proposed layout, only one window would be needed. Because the rotation angle is never more than 1 "fringe,'' the data is always good, and it is also a continuous measurement in time. Faraday rotation is dependent only upon the plasma itself, and thus is not sensitive to vibration of the optical components. Simulations of the expected results show that ITER, or any large tokamak, existing or proposed, would be well served even at low densities by a midplane Faraday rotation densitometer of ∼64 channels.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143465
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  • 2
    Electronic Resource
    Electronic Resource
    Lithium pellet deposition and penetration in TFTR : Proceedings of the 9th topical conference on high temperature plasma diagnostics (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 4984-4986 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The electron deposition resulting from the injection of Li pellets into Tokamak Fusion Test Reactor, measured by a multichannel (10) infrared interferometer, is compared with that deduced from the pellet ablation cloud emission, measured by a filtered diode array which views the pellet from behind. By assuming that the ablation rate N(overdot)(r) is proportional to the pellet cloud emissivity, which is dominated by Li+ line emission in the 548.5±5 nm bandpass of the interference filter, the post-pellet, line averaged density perturbations along the interferometer chords were calculated and compared with those measured. Good agreement is observed. The experimental ablation rate profiles obtained using the emissivity have also been compared with predictions of the theoretical models. There is an agreement between the time history of the emissivity and the predicted ablation rate at the plasma edge where the electron temperature values are less than 1–1.5 keV. When the pellet penetrates more deeply, the experimental N(overdot)(r) values are systematically smaller than those predicted. This points out the necessity of taking into account plasma shielding and/or precooling of the target plasma during pellet injection in the ablation model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143521
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  • 3
    Electronic Resource
    Electronic Resource
    Application of TFTR diagnostics to study of limiter H-modes (1990)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 61 (1990), S. 3532-3535 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Circular limiter H modes with centrally peaked density profiles have been obtained on TFTR. Diagnostics used to study these unique plasmas include arrays of Dα and C ii detectors, bolometers, and Mirnov coils; x-ray imaging, charge exchange recombination spectroscopy, ECE, microwave scattering systems, and a multichannel infrared interferometer. These diagnostics have special features which allow time and space-resolved measurements during the H-mode transition and during ELMs. Microwave scattering during the H phase shows a feature in the scattered spectrum which is consistent with a poloidal rotation in the electron diamagnetic drift direction. Mirnov coil data digitized at 2 MHz show an increase in high-frequency magnetic fluctuations (60–200 kHz) during an ELM, while ECE data show 20–30 μs intense emission spikes in the outer 15–20 cm of the plasma edge.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1141564
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  • 4
    Electronic Resource
    Electronic Resource
    Scaling of Ohmic energy confinement with major radius in the Tokamak Fusion Test Reactor (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 3996-4001 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ohmic plasma size scans have been carried out in the Tokamak Fusion Test Reactor (TFTR) [Fusion Technol. 21, 1324 (1992)] to measure the influence of the major radius upon energy confinement. The major radius, minor radius, and aspect ratio were varied over wide ranges (R=2.08–3.2 m, a=0.4–0.9 m, and R/a=2.9–8.0) at constant qc. The energy confinement determined from kinetic diagnostics varies strongly with major radius. The data set is less well suited to determine minor radius scaling, but it appears to be distinctly weaker than the major radius scaling. The anomaly in ion thermal conductivity over neoclassical predictions appears to decline with increasing aspect ratio, which is a better ordering parameter for the magnitude of the anomaly than either the minor radius or the major radius. © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870869
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  • 5
    Electronic Resource
    Electronic Resource
    Application of TFTR diagnostics to study of limiter H modes (abstract) : Eighth topical conference on high-temperature plasma diagnostics (1990)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 61 (1990), S. 3307-3307 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Circular limiter H modes with centrally peaked density profiles have been obtained on TFTR. Diagnostics used to study these unique plasmas include arrays of Dα and C ii detectors, bolometers, and Mirnov coils; x-ray imaging, charge exchange recombination spectroscopy, ECE, microwave scattering systems, and a multichannel infrared interferometer. These diagnostics have special features which allow time and space-resolved measurements during the H-mode transition and during ELMs. Microwave scattering during the H phase shows a feature in the scattered spectrum which is consistent with a poloidal rotation in the electron diamagnetic drift direction. Mirnov coil data digitized at 2 MHz show an increase in high-frequency magnetic fluctuations (60–200 kHz) during an ELM, while ECE data show 20–30 μs intense emission spikes in the outer 15–20 cm of the plasma edge.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1141625
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  • 6
    Electronic Resource
    Electronic Resource
    Helium, iron, and electron particle transport and energy transport studies on the Tokamak Fusion Test Reactor (1993)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 2215-2228 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Results from helium, iron, and electron transport studies on the Tokamak Fusion Test Reactor (TFTR) [Plasma Phys. Controlled Nucl. Fusion Res. 26, 11 (1984)] in L-mode and supershot deuterium plasmas with the same toroidal field, plasma current, and neutral beam heating power are presented. They are compared to results from thermal transport analysis based on power balance. Particle diffusivities and thermal conductivities are radially hollow and larger than neoclassical values, except possibly near the magnetic axis. The ion channel dominates over the electron channel in both particle and thermal diffusion. A peaked helium profile, supported by inward convection that is stronger than predicted by neoclassical theory, is measured in the supershot. The helium profile shape is consistent with predictions from quasilinear electrostatic drift-wave theory. While the perturbative particle diffusion coefficients of all three species are similar in the supershot, differences are found in the L mode. Quasilinear theory calculations of the ratios of impurity diffusivities are in good accord with measurements. Theory estimates indicate that the ion heat flux should be larger than the electron heat flux, consistent with power balance analysis. However, theoretical values of the ratio of the ion to electron heat flux can be more than a factor of 3 larger than experimental values. A correlation between helium diffusion and ion thermal transport is observed and has favorable implications for sustained ignition of a tokamak fusion reactor.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860755
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  • 7
    Electronic Resource
    Electronic Resource
    High-Q plasmas in the TFTR tokamak (1991)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 2308-2314 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In the Tokamak Fusion Test Reactor (TFTR) [Plasma Phys. Controlled Fusion 26, 11 (1984)], the highest neutron source strength Sn and D–D fusion power gain QDD are realized in the neutral-beam-fueled and heated "supershot'' regime that occurs after extensive wall conditioning to minimize recycling. For the best supershots, Sn increases approximately as P1.8b. The highest-Q shots are characterized by high Te (up to 12 keV), Ti (up to 34 keV), and stored energy (up to 4.7 MJ), highly peaked density profiles, broad Te profiles, and lower Zeff. Replacement of critical areas of the graphite limiter tiles with carbon-fiber composite tiles and improved alignment with the plasma have mitigated the "carbon bloom.'' Wall conditioning by lithium pellet injection prior to the beam pulse reduces carbon influx and particle recycling. Empirically, QDD increases with decreasing pre-injection carbon radiation, and increases strongly with density peakedness [ne(0)/〈ne〉] during the beam pulse. To date, the best fusion results are Sn=5×1016 n/sec, QDD=1.85×10−3, and neutron yield=4.0×1016 n/pulse, obtained at Ip=1.6–1.9 MA and beam energy Eb=95–103 keV, with nearly balanced co- and counter-injected beam power. Computer simulations of supershot plasmas show that typically 50%–60% of Sn arises from beam–target reactions, with the remainder divided between beam–beam and thermonuclear reactions, the thermonuclear fraction increasing with Pb. The simulations predict that QDT=0.3–0.4 would be obtained for the best present plasma conditions, if half the deuterium neutral beams were to be replaced by tritium beams. Somewhat higher values are calculated if D beams are injected into a predominantly tritium target plasma. The projected central beta of fusion alphas is 0.4%–0.6%, a level sufficient for the study of alpha-induced collective effects.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859988
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  • 8
    Electronic Resource
    Electronic Resource
    High poloidal beta long-pulse experiments in the Tokamak Fusion Test Reactorf| (1993)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 2525-2531 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Experiments have been performed in the Tokamak Fusion Test Reactor [D. M. Meade et al. in Plasma Physics Controlled Nuclear Fusion Research, 1990 (International Atomic Energy Agency, Vienna, 1991), Vol. 1, p. 9] with neutral beam injection of up to 4 sec. duration, which is comparable to the time scale for resistive redistribution of the plasma current profile. These plasmas were created using a rapid decrease of the plasma current which initially created a plasma with enhanced stability and confinement. As the current profile evolved, a significantly reduced beta limit was observed. The high εβp plasmas had up to 90% of the current driven noninductively which significantly broadened the current profile during the long pulse lengths. These experiments demonstrated that high βN plasmas could not be sustained for times longer than the resistive relaxation of the outer current region which at early times after the current ramp-down carried negative current. At later times in lower βN discharges, beta collapses were sometimes observed as the current profile broadened at βN∼1.5. The appearance of disruptions was consistent with the predictions of ideal magnetohydrodynamics (MHD) stability analyses.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860739
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  • 9
    Electronic Resource
    Electronic Resource
    Comparison of steady-state and perturbative transport coefficients in TFTR (1991)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 2315-2323 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Steady-state and perturbative transport analysis are complementary techniques for the study of transport in tokamaks. These techniques are applied to the investigation of auxiliary-heated L-mode and supershot plasmas in the tokamak fusion test reactor (TFTR) [R. J. Hawryluk et al., Plasma Physics and Controlled Nuclear Fusion Research, Proceedings of the 11th International Conference, Kyoto, 1986 (IAEA, Vienna, 1987), Vol. 1, p. 51.]. In the L mode, both steady-state and perturbative transport measurements reveal a strong temperature dependence that is consistent with electrostatic microinstability theory and the degradation of confinement with neutral beam power. Steady-state analysis of the ion heat and momentum balance in supershots indicates a reduction and a significant weakening of the power-law dependence on the transport in the center of the discharge.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859598
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  • 10
    Electronic Resource
    Electronic Resource
    Ion cyclotron range of frequency heating on the Tokamak Fusion Test Reactorf| (1993)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 2437-2444 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The complete ion cyclotron range of frequency (ICRF) heating system for the Tokamak Fusion Test Reactor (TFTR) [Fusion Tech. 21, 1324 (1992)], consisting of four antennas and six generators designed to deliver 12.5 MW to the TFTR plasma, has now been installed. Recently a series of experiments has been conducted to explore the effect of ICRF heating on the performance of low recycling, supershot plasmas in minority and nonresonant electron heating regimes. The addition of up to 7.4 MW of ICRF power to full size (R∼2.6 m, a∼0.95 m), helium-3 minority, deuterium supershots heated with up to 30 MW of deuterium neutral-beam injection has resulted in a significant increase in core electron temperature (ΔTe=3–4 keV). Simulations of equivalent deuterium–tritium (D–T) supershots predict that such ICRF heating should result in an increase in βα(0)∼30%. Direct electron heating has been observed and has been found to be in agreement with theory. The ICRF heating has also been coupled to neutral-beam heated plasmas fueled by frozen deuterium pellets. In addition ICRF heated energetic ion tails have been used to simulate fusion alpha particles in high-recycling plasmas. Up to 11.4 MW of ICRF heating has been coupled into a hydrogen minority, high-recycling helium plasma and the first observation of the toroidal Alfvén eigenmode (TAE) instability driven by the energetic proton tail has been made in this regime.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860728
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