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  • 1
    Digitale Medien
    Digitale Medien
    High density, high performance high-confinement-mode plasmas in the Joint European Torus (JET) : Review,Tutorial and Invited Papers from the 43rd Annual Meeting of the APS Division of Plasma Physics (2002)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 9 (2002), S. 2103-2112 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Recent experiments at the Joint European Torus [Rebut et al., Fusion Eng. Des. 22, 7 (1993)] aim to improve confinement quality in high-confinement-mode (H-mode) plasmas at high densities. Energy confinement time as predicted by the International Thermonuclear Experimental Reactor ITER-H98(y,2) scaling at densities near or in excess of 85% of the Greenwald density limit scaling has been obtained by (i) strong plasma shaping (triangularity 0.35〈δ〈0.5), or (ii) impurity seeding, or (iii) high-field side pellet injection. Slow peaking of central density without confinement degradation is observed. Loss of sawteeth and core impurity accumulation is prevented by central ion cyclotron resonance heating. In high triangularity and impurity seeded plasmas, reduction of average power loss associated with type I edge localized modes (ELMs) is found which is attributed to the occurrence of additional losses in between ELMs. Broad band magnetic fluctuations are seen which are reminiscent of regimes with small ELMs in other tokamaks. Plasma configurations have been varied to find best combinations of edge pedestal parameters and small ELM losses. © 2002 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1456067
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  • 2
    Digitale Medien
    Digitale Medien
    Investigation of tritium pathways in the Joint European Torus (JET) tokamak : 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. 1985-1994 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The neutral tritium concentration in the subdivertor region of JET [P.-H. Rebut, R. J. Bickerton, and B. E. Keen, Nucl. Fusion 25, 1011 (1985)] is measured during deuterium-to-tritium changeover experiments with a novel species-selective Penning gauge coupled to a high-resolution spectrometer. The subdivertor measurements, when compared with edge and strike point values, are a sensitive characterization of the status of the wall saturation. The neutral transport code (EIRENE) [D. Reiter, Forschungszentrum, Juelich: Report Juel-2599 (1992)] and a wall hydrogen trapping and diffusion code (WDIFFUSE) [J. Hogan, R. Maingi, P. Mioduszewski et al., J. Nucl. Mater. 241, 612 (1997)] evaluate the wall tritium recycling coefficients (RT) and compare them with quantitative, testable models for the dynamic exchange between recycling surfaces and the edge/pedestal region. Using the dynamic inventory model, tritium transport following the injection of trace amounts of tritium has been investigated for JET high-confinement mode (H-mode) discharges with Edge Localized Modes (ELMs). Upon explicitly treating the ELMs as instantaneous magnetohydrodynamic events, residual (intra-ELM) radial diffusivities are reduced and can be compared with neoclassical levels. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.873454
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  • 3
    Digitale Medien
    Digitale Medien
    Helium transport and exhaust studies in enhanced confinement regimes in DIII-D (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 2357-2365 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A better understanding of helium transport in the plasma core and edge in enhanced confinement regimes is now emerging from recent experimental studies on DIII-D [Plasma Physics and Controlled Fusion Research (International Atomic Energy Agency, Vienna, 1986), p. 159]. Overall, the results are encouraging. Significant helium exhaust (τHe*/τE∼11) has been obtained in a diverted, H-mode plasma with edge-localized modes (ELM's) simultaneous with a central source of helium. There is no evidence of central peaking of the helium density profile even in the presence of this central source. Detailed analysis of the helium profile evolution indicates that the exhaust rate is limited by the exhaust efficiency of the pump (∼5%) and not by the intrinsic helium transport properties of the plasma. Perturbative helium transport studies using gas puffing have shown that DHe/χeff ∼1 in all confinement regimes studied to date (including H mode and VH mode). Furthermore, there is no evidence of preferential accumulation of helium in any of these regimes. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.871489
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  • 4
    Digitale Medien
    Digitale Medien
    Recent progress toward high performance above the Greenwald density limit in impurity seeded discharges in limiter and divertor tokamaks : The 42nd annual meeting of the division of plasma physics of the American Physical Society and the 10th international congress on plasma physics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 2188-2198 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: An overview is given of recent advances toward the realization of high density, high confinement plasmas with radiating mantles in limiter and divertor tokamaks worldwide. Radiatively improved mode discharges on the Torus Experiment for Technology Oriented Research 94 (TEXTOR-94) [Proceedings of the 16th IEEE Symposium on Fusion Engineering, 1995 (Institute for Electrical and Electronics Engineers, Piscataway, NJ, 1995), p. 470] have recently been obtained at trans-Greenwald densities (up to n¯/nGW=1.4) with high confinement mode free of edge localized modes (ELM-free H-mode) confinement quality. Experiments in DIII-D [J. Luxon et al., Proceedings of the 11th IAEA Conference on Plasma Physics and Controlled Nuclear Fusion Research (International Atomic Energy Association, Vienna, 1987), Vol. 1, p. 159] divertor plasmas with a low confinement mode edge have confirmed the dramatic changes in confinement observed with impurity seeding on TEXTOR-94. Recent experiment with impurity seeding on the Joint European Torus [Rebut et al., Fusion Eng. Des. 22, 7 (1993)], and the Japanese Atomic Energy Research Institute Tokamak 60 Upgrade [Horiike et al., Fusion Eng. Des. 16, 285 (1991); Hosogane et al., Proceedings of the 16th IAEA Conference on Plasma Physics and Controlled Nuclear Fusion Research Montreal, 1987 (International Atomic Energy Association, Vienna, 1987), Vol. 3, p. 555] have extended high confinement in ELMy H-mode plasmas to higher densities. Finally, recent progress in the physical understanding of radiating mantle plasmas is summarized. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1364513
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  • 5
    Digitale Medien
    Digitale Medien
    Effects of neutron energy spectrum on the efficiency calibration of epithermal neutron detectors (1985)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 56 (1985), S. 1084-1086 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: The 235U epithermal neutron fission detector system at TFTR has been calibrated in situ, using three different neutron sources: 252Cf, a D-D, and a D-T neutron generator. These sources produced a continuous spectrum, a line spectrum at ∼2.5 MeV, and a line spectrum at ∼14 MeV, respectively. The toroidally averaged detection efficiencies are 4.61×10−9 (252Cf), 4.80×10−9 (D-D), and 5.42×10−9 (D-T) counts/neutron for a moderated 1.3-g 235U detector placed ∼4 m from the torus centerline. The effects of (n,2n) and (n,n'γ) reactions are discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1138230
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  • 6
    Digitale Medien
    Digitale Medien
    Tritium concentration measurements in the Joint European Torus divertor by optical spectroscopy of a Penning discharge : 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. 359-362 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Obtaining precision measurements of the relative concentrations of hydrogen, deuterium, tritium, and helium in the divertor of a tokamak is an important task for nuclear fusion research. Control of the deuterium–tritium isotopic ratio while limiting the helium ash content in a fusion plasma are key factors for optimizing the fuel burn in a fusion reactor, like the International Tokamak Experimental Reactor. A diagnostic technique has been developed to measure the deuterium–tritium isotopic ratio in the divertor of the Joint European Torus with a species-selective Penning vacuum gauge. The Penning discharge provides a source of electrons to excite the neutral hydrogen isotopes in the pumping duct. Subsequently, the visible light from the hydrogen isotopes is collected in an optical fiber bundle, transferred away from the tokamak into a low radiation background area, and analyzed in a high resolution Czerny–Turner spectrometer, which is equipped with a fast charge coupled device camera for optical detection. The intensity of the observed line emission (Dα−6561.03 Å and Tα−6560.44 Å) is directly proportional to the partial pressure of each gas found in the divertor. The line intensity of each isotope is calibrated as a function of pressure. The ratio of the line intensities thus provides a direct measurement of the deuterium–tritium isotopic ratio. The lower limit for the determination of the deuterium–tritium isotopic ratio is about 0.5%. The applicable pressure range for this system is from 10−5 to a few times 10−3 mbar. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1149301
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  • 7
    Digitale Medien
    Digitale Medien
    Application of a species-selective Penning gauge to the measurement of neon and hydrogen-isotope partial pressures in the plasma boundary : 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. 400-403 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: A species-selective Penning gauge, previously applied to He partial pressures, is now applied to the detection of small concentrations of Ne in a D2 gas. This is important for the study of Ne in the boundary region of magnetic fusion devices, where this impurity is deliberately injected to enhance the radiated power in that region. The application of the technique to the detection of the partial pressure of a minority hydrogen isotope is also examined. In this latter application, the detection system and the data analysis are more complex, because of the proximity of the spectral lines of the isotopes. In both applications, it is found that use of a proper detection scheme permits reliable measurements of concentrations as low as 0.5% of the minority neutral species, without requiring changes to the standard commercial Penning gauge setup. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1147839
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  • 8
    Digitale Medien
    Digitale Medien
    Electron beam and magnetic field mapping techniques used to determine field errors in the ATF torsatron (1989)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 60 (1989), S. 2680-2689 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: The beam from an electron gun was used to trace flux surfaces in the Advanced Toroidal Facility (ATF) torsatron. The ATF magnetic field was run steady state at 0.1 T, and the electron beam was detected optically with an image-intensified, solid-state camera when it impinged on a phosphor-coated screen. Closed flux surfaces and islands at several low-order resonances were observed. The largest island, located at the ι= 1/2 surface, was from 5 to 6 cm in width, and its presence implied the existence of magnetic field errors. To determine if these error fields could be traced to small misalignments of the magnetic coils, a device capable of accurately measuring the radial and vertical magnetic field components of individual coil sets was placed in the center of ATF. This device allowed for a determination of the precise location of each of the coils that make up the ATF coil set. No significant coil misalignments were found. A further investigation of the coil configuration led to the identification of dipole fields in the helical field coil leads as the source of the field errors. The techniques developed in making these measurements are described in the text.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1141082
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  • 9
    Digitale Medien
    Digitale Medien
    Image analysis and data-acquisition techniques for infrared and CCD cameras for ATF (1988)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 59 (1988), S. 1762-1764 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: A multipurpose image processing system has been developed for the Advanced Toroidal Facility (ATF) stellarator experiment. This system makes it possible to investigate the complicated topology inherent in stellarator plasmas with conventional video technology. Infrared (IR) and charge-coupled device (CCD) cameras, operated at the standard video framing rate, are used on ATF to measure heat flux patterns to the vacuum vessel wall and visible-light emission from the ionized plasma. These video cameras are coupled with fast acquisition and display systems, developed for a MicroVAX-II, which allow between-shot observation of the dynamic temperature and spatial extent of the plasma generated by ATF. The IR camera system provides acquisition of one frame of 60×80 eight-bit pixels every 16.7 ms via storage in a CAMAC module. The CCD data acquisition proceeds automatically, storing the video frames until its 12-bit, 1-Mbyte CAMAC memory is filled. After analysis, transformation, and compression, selected portions of the data are stored on disk. Interactive display of experimental data and theoretical calculations are performed with software written in Interactive Data Language.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1140104
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  • 10
    Digitale Medien
    Digitale Medien
    Multiple-frequency electron-cyclotron heating of hot-electron rings in a bumpy torus (1985)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 28 (1985), S. 1932-1936 
    Details
    ISSN: 1089-7666
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The use of multiple-frequency microwave power for electron-cyclotron heating significantly increased the ring stored energy in the SM-1 simple mirror device. Multiple-frequency electron-cyclotron heating (MFECH) was used on the ELMO Bumpy torus (EBT) in an effort to increase its hot-electron beta. No substantial improvement in the ring parameters was observed in a series of two-frequency ECH experiments, with frequency separations up to 90 MHz, in contrast to the dramatic improvement found in the axisymmetric SM-1 experiment. The toroidal canting of the EBT mirror sectors introduces asymmetries that destroy the superadiabatic behavior of the energetic electrons, reduce microwave heating efficiency, and produce additional ring losses. These effects qualitatively explain the different multiple-frequency heating results obtained in EBT and SM-1.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.864937
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