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  • 1995-1999  (11)
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  • 1
    Electronic Resource
    Electronic Resource
    Enhancement of Tokamak Fusion Test Reactor performance by lithium conditioning (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 1892-1897 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Wall conditioning in the Tokamak Fusion Test Reactor (TFTR) [K. M. McGuire et al., Phys. Plasmas 2, 2176 (1995)] by injection of lithium pellets into the plasma has resulted in large improvements in deuterium–tritium fusion power production (up to 10.7 MW), the Lawson triple product (up to 1021 m−3 s keV), and energy confinement time (up to 330 ms). The maximum plasma current for access to high-performance supershots has been increased from 1.9 to 2.7 MA, leading to stable operation at plasma stored energy values greater than 5 MJ. The amount of lithium on the limiter and the effectiveness of its action are maximized through (1) distributing the Li over the limiter surface by injection of four Li pellets into Ohmic plasmas of increasing major and minor radius, and (2) injection of four Li pellets into the Ohmic phase of supershot discharges before neutral-beam heating is begun. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871984
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  • 2
    Electronic Resource
    Electronic Resource
    Tests of local transport theory and reduced wall impurity influx with highly radiative plasmas in the Tokamak Fusion Test Reactor (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 877-884 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The electron temperature (Te) profile in neutral beam-heated supershot plasmas (Te0∼6–7 keV ion temperature Ti0∼15–20 keV, beam power Pb∼16 MW) was remarkably invariant when radiative losses were increased significantly through gas puffing of krypton and xenon in the Tokamak Fusion Test Reactor [McGuire et al., Phys. Plasmas 2, 2176 (1995)]. Trace impurity concentrations (nz/ne∼10−3) generated almost flat and centrally peaked radiation profiles, respectively, and increased the radiative losses to 45%–90% of the input power (from the normal ∼25%). Energy confinement was not degraded at radiated power fractions up to 80%. A 20%–30% increase in Ti, in spite of an increase in ion–electron power loss, implies a factor of ∼3 drop in the local ion thermal diffusivity. These experiments form the basis for a nearly ideal test of transport theory, since the change in the beam heating power profile is modest, while the distribution of power flow between (1) radiation and (2) conduction plus convection changes radically and is locally measurable. The decrease in Te was significantly less than predicted by two transport models and may provide important tests of more complete transport models. At input power levels of 30 MW, the increased radiation eliminated the catastrophic carbon influx (carbon "bloom") and performance (energy confinement and neutron production) was improved significantly relative to that of matched shots without impurity gas puffing. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873327
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  • 3
    Electronic Resource
    Electronic Resource
    Confinement analysis in low-confinement mode of hydrogen isotope experiments on the Tokamak Fusion Test Reactor (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 4521-4535 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of isotope on confinement in high-recycling, L-mode plasmas is studied on the Tokamak Fusion Test Reactor (TFTR) [see D. M. Meade, J. Fusion Energy 7, 107 (1988)] by comparing hydrogen and deuterium plasmas with the same magnetic field and similar electron densities and heating power, with both Ohmic and deuterium-neutral-beam heating. Following a long operational period in deuterium, nominally hydrogen plasmas were created through hydrogen glow discharge and hydrogen gas puffing in Ohmic plasmas, which saturated the exposed limiter surface with hydrogen and raised the H/(H+D) ratio from 10±3% to 65±5%. Ohmic deuterium discharges obtained higher stored energy and lower loop voltage than hydrogen discharges with similar limiter conditions. Neutral-beam power scans were conducted in L-mode plasmas at minor radii of 50 and 80 cm, with plasma currents of 0.7 and 1.4 MA. To minimize transport differences from the beam deposition profile and beam heating, deuterium neutral beams were used to heat the plasmas of both isotopes. Total stored energy increased approximately 20% from nominally hydrogen plasmas to deuterium plasmas during auxiliary heating. Of this increase about half can be attributed to purely classical differences in the energy content of unthermalized beam ions. Kinetic measurements indicate a consistent but small increase in central electron temperature and total stored electron energy in deuterium relative to hydrogen plasmas, but no change in total ion stored energy. No significant differences in particle transport, momentum transport, and sawtooth behavior are observed. Overall, only a small improvement (∼10%) in global energy confinement time of the thermal plasma is seen between operation in hydrogen and deuterium. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872069
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  • 4
    Electronic Resource
    Electronic Resource
    Enhanced performance of deuterium–tritium-fueled supershots using extensive lithium conditioning in the Tokamak Fusion Test Reactor (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 4252-4256 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In the Tokamak Fusion Test Reactor (TFTR) [K. M. McGuire et al., Phys. Plasmas 2, 2176 (1995)] a substantial improvement in fusion performance has been realized by combining the enhanced confinement due to tritium fueling with the enhanced confinement due to extensive conditioning of the limiter with lithium. This combination has resulted in not only significantly higher global energy confinement times than have previously been obtained in high current supershots, but also in the highest central ratio of thermonuclear fusion output power to input power observed to date. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871050
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  • 5
    Electronic Resource
    Electronic Resource
    Imaging x-ray crystal spectrometers for the National Spherical Torus Experiment : 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. 292-295 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A new type of high-resolution x-ray imaging crystal spectrometers is described for implementation on the National Spherical Torus Experiment (NSTX) to provide spatially and temporally resolved data on the ion temperature, toroidal and poloidal plasma rotation, electron temperature, impurity ion-charge state distributions, and impurity transport. These data are derived from observations of the satellite spectra of heliumlike argon, Ar XVII, which is the dominant charge state for electron temperatures in the range from 0.4 to 3.0 keV and which is accessible to NSTX. Experiments at the Torus Experiment for Technology Oriented Research (TEXTOR) demonstrate that a throughput of 2×105 photons/s (corresponding to the count-rate limit of the present detectors) can easily be obtained with small, nonperturbing argon gas puffs of less than 1×10−3 Torr l/s, so that it is possible to record spectra with a small statistical error and a good time resolution (typically 50 and 1 ms in some cases). Employing a novel design, which is based on the imaging properties of spherically bent crystals, the spectrometers will provide spectrally and spatially resolved images of the plasma for all experimental conditions, which include ohmically heated discharges as well as plasmas with rf and neutral-beam heating. The conceptual design, experimental results on the focusing properties, and relevant spectral data from TEXTOR are presented. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149344
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  • 6
    Electronic Resource
    Electronic Resource
    Zeff profiles measured by visible and soft x-ray bremsstrahlung arrays in TFTR (abstract)a) : 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. 635-635 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The Zeff profiles from the tangential array of visible bremsstrahlung (VB) emission (5235 A(ring)) have shown several interesting features in TFTR. The observed Zeff profile was flat during the ohmic phase and hollow during the neutral-beam heating phase. In order to crosscheck the measured Zeff profiles from the VB array, a poloidal array which measures bremsstrahlung emission in the soft x-ray region has been analyzed. The analysis of array measurements in the two different spectral regions was performed on the same geometry determined from the Abel inversion of the electron density (interferometry). The two independent measurements of Zeff profiles have been consistent with each other for most of the discharges in TFTR. However, in a discharge where the two measurements are inconsistent, the Zeff profile deduced from the VB array indicates some degree of problems. In this paper, the detailed analysis of the bremsstrahlung array (both poloidal and tangential) measurements is presented. Particularly, the effects of geometry in the inversion process, such as a poloidal elongation of flux surfaces, are investigated. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146310
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  • 7
    Electronic Resource
    Electronic Resource
    Luminescence and transmission measurements on fibers exposed to high neutron fluxes : 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. 904-906 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Fiber-based diagnostic systems suffer from induced luminescence and transmission losses due to neutron and γ radiation from high-power D-D and D-T discharges. Whereas the luminescence follows the neutron rate, the transmission loss increases monotonically during a shot and decays slowly after the discharge. To study these effects we are using dedicated fiber coils (increasing the exposed length) which are positioned close to the discharge vessel (increasing the neutron flux) and close to neutron detectors. The fibers studied are typical for diagnostics on TFTR. One fiber is of the same type used for the JET/TFTR heated fiber study. We measure spectrally selected luminescence and transmission with a light emitting diode based, modulated three-phase exciter system. We have measured substantial transmission losses during D-T shots which reduce the test signals and the radioluminescence. The transmission losses recover only partially; we will show first long-term measurements of the loss recovery. A simple model is presented which allows the derivation of values for luminescence source strength per length unit and neutron flux even if the luminescence is reduced by the induced transmission loss. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146201
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  • 8
    Electronic Resource
    Electronic Resource
    Analysis of nuclear-radiation-induced noise in spectroscopic and x-ray diagnostics during high power deuterium–tritium experiments on the tokamak fusion test reactor : 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. 913-915 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Intense fluxes of 14-MeV neutrons from deuterium–tritium (DT) fusion reaction in TFTR resulted in significantly enhanced background noise levels and reduced quality of data from the shielded UV (SPRED) and visible (VIPS) grating spectrometers and the x-ray imaging system (XIS) camera. Both enhanced background levels, attributed to gamma rays and small angle neutron scattering, and large spikes, attributed to nuclear reactions in the silicon detectors, were observed. Both the enhanced background and the frequency of spikes were higher, on a per neutron basis, and the spike amplitudes were higher for DT than for DD operation. The VIPS shield reduced noise by 1/100 for DD radiation; the noise per DT neutron was 4 times higher than per DD neutron. The SPRED detector shield reduction factor was 1/12 in DD; extension of the shield around the vacuum chamber resulted in another factor of 1/5.5 reduction for DT plasmas. Spikes with amplitude up to 10 MeV were observed in the XIS detectors. The shielding effectiveness agrees with predictions. The spike heights are consistent with (n,p) and (n,α) reactions in the silicon detectors. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146203
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  • 9
    Electronic Resource
    Electronic Resource
    Numerical studies of the imaging properties of doubly focussing crystals and their application to ITER : 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. 530-532 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Line brightness calculations for the parameters at the International Thermonuclear Experimental Reactor (ITER) and results from recent experiments on the Tokamak Fusion Test Reactor (TFTR) indicate that time-resolved measurements of the central ion temperature and other central plasma parameters should be feasible on ITER with nonperturbing amounts of krypton. Since the measurements will have to be performed in the presence of high fluxes of 14-MeV neutrons from DT-fusion reactions, the size of windows, apertures and x-ray detectors must be as small as possible. Under these conditions, the use of doubly focussing crystals can significantly enhance the signal-to-noise ratio. This paper describes numerical studies of the focussing properties of spherically bent crystals and their application to ITER. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146341
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  • 10
    Electronic Resource
    Electronic Resource
    A new device for injection of iron atoms into plasmas : 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. 568-570 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Reduction of indigenous metal impurities in tokamak plasmas and impurity requirements for the x-ray diagnosis of central plasma parameters necessitates artificial introduction of metal atoms. A new inexpensive method is described using ferrocene, Fe(C5H5)2, a substance which sublimes. A prototype device was tested at the Atomic-Beam Facility at PPPL. Ferrocene was injected into a pulsed helium plasma with an electron density of 2×1013 cm−3 and an electron temperature of 5 eV. The injected amount of ferrocene was controlled by varying the sublimation temperature in the range from 70 to 150 °C and adjusting the pulse length of a solenoid valve; the resulting iron atom concentration in the plasma was determined by monitoring the intensity of the Fe line at 5269 A(ring). The device and the test results are presented. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146287
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