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  • 1
    Electronic Resource
    Electronic Resource
    Spinal clear cell meningioma presented with progressive paraparesis in infancy (2000)
    Springer
    Child's nervous system 16 (2000), S. 607-610 
    Details
    ISSN: 1433-0350
    Keywords: Keywords Spinal clear cell meningioma ; Infancy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  Clear cell meningioma, about 20 cases of which have been reported in the literature, is a morphological variant of meningioma. The authors report a case of spinal clear cell meningioma that occurred in a child. A 14-month-old girl showed gradually progressive paraparesis 1 month after she started to walk. Magnetic resonance image showed an intradural extramedullary mass compressing the conus medullaris and cauda equina. Complete excision of the tumor was done, and the patient gradually recovered from motor weakness and neurogenic bladder. Histological examinations along with immunohistochemical and ultrastructural investigations allowed a diagnosis of clear cell meningioma. During the follow-up period, a recurrent mass lesion was detected on the 8-month follow-up MR image in the same region. Because clear cell meningioma might be biologically aggressive, postoperative adjuvant therapy and close follow-up investigation should be considered.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00007302
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  • 2
    Electronic Resource
    Electronic Resource
    Transitionless enhanced confinement and the role of radial electric field shear (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 615-625 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Evidence is presented for the role of radial electric field shear in enhanced confinement regimes attained without sharp bifurcations or transitions. Temperature scans at constant density, created in the reheat phase following deuterium pellet injection into supershot plasmas in the Tokamak Fusion Test Reactor [J. D. Strachan, et al., Phys. Rev. Lett. 58, 1004 (1987)] are simulated using a physics-based transport model. The slow reheat of the ion temperature profile, during which the temperature nearly doubles, is not explained by relatively comprehensive models of transport due to Ion Temperature Gradient Driven Turbulence (ITGDT), which depends primarily on the (unchanging) electron density gradient. An extended model, including the suppression of toroidal ITGDT by self-consistent radial electric field shear, does reproduce the reheat phase. The extended reheat at constant density is observed in supershot but not L-Mode plasmas. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873867
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  • 3
    Electronic Resource
    Electronic Resource
    The role of the neutral beam fueling profile in the performance of the Tokamak Fusion Test Reactor and other tokamak plasmas : 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. 1699-1706 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Scalings for the stored energy and neutron yield, determined from experimental data, are applied to both deuterium-only and deuterium–tritium plasmas in different neutral-beam-heated operational domains in the Tokamak Fusion Test Reactor [Nucl. Fusion 25, 1167 (1985)]. The domain of the data considered includes the Supershot, high poloidal beta, low-mode, and limiter high-mode operational regimes, as well as discharges with a reversed magnetic shear configuration. The new important parameter in the present scaling is the peakedness of the heating beam fueling profile shape. Ion energy confinement and neutron production are relatively insensitive to other plasma parameters compared to the beam fueling peakedness parameter and the heating beam power when considering plasmas that are stable to magnetohydrodynamic modes. However, the stored energy of the electrons is independent of the beam fueling peakedness. The implication of the scalings based on this parameter is related to theoretical transport models such as radial electric field shear and ion temperature gradient marginality models. Similar physics interpretation is provided for beam heated discharges on other major tokamaks.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872272
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  • 4
    Electronic Resource
    Electronic Resource
    Confinement and the safety factor profile (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 1348-1355 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The conjecture that the safety factor profile, q(r), controls the improvement in tokamak plasmas from poor confinement in the Low- (L-) mode regime to improved confinement in the supershot regime has been tested in two experiments on the Tokamak Fusion Test Reactor (TFTR) [Plasma Phys. Controlled Nucl. Fusion Res. 1, 51 (1987)]. First, helium was puffed into the beam-heated phase of a supershot discharge, which induced a degradation from supershot to L-mode confinement in about 100 ms, far less than the current relaxation time. The q and shear profiles measured by a motional Stark effect polarimeter showed little change during the confinement degradation. Second, rapid current ramps in supershot plasmas altered the q profile, but were observed not to change significantly the energy confinement. Thus, enhanced confinement in supershot plasmas is not due to a particular q profile, which has enhanced stability or transport properties. The discharges making a continuous transition between supershot and L-mode confinement were also used to test the critical-electron-temperature-gradient transport model. It was found that this model could not reproduce the large changes in electron and ion temperature caused by the change in confinement. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871788
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  • 5
    Electronic Resource
    Electronic Resource
    Isotopic scaling of confinement in deuterium–tritium plasmas (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 2299-2307 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The confinement and heating of supershot plasmas are significantly enhanced with tritium beam injection relative to deuterium injection in the Tokamak Fusion Test Reactor [Plasma Phys. Controlled Fusion 26, 11 (1984)]. The global energy confinement and local thermal transport are analyzed for deuterium and tritium fueled plasmas to quantify their dependence on the average mass of the hydrogenic ions. Radial profiles of the deuterium and tritium densities are determined from the D–T fusion neutron emission profile. The inferred scalings with average isotopic mass are quite strong, with τE∝〈A〉0.85±0.20, τEthermal∝〈A〉0.89±0.20, χitot∝〈A〉−2.6±0.5, and De∝〈A〉−1.4±0.2 at fixed Pinj. For fixed local plasma parameters χitot∝〈A〉−1.8±0.4 is obtained. The quoted 2σ uncertainties include contributions from both diagnostic errors and shot irreproducibility, and are conservatively constructed to attribute the entire scatter in the regressed parameters to uncertainties in the exponent on plasma mass. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871253
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  • 6
    Electronic Resource
    Electronic Resource
    High-frequency core localized modes in neutral beam heated plasmas on TFTR (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 593-605 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A band of high-frequency modes in the range 50–150 kHz with intermediate toroidal mode numbers 4〈n〈10 are commonly observed in the core of supershot plasmas on TFTR [R. Hawryluk, Plasma Phys. Controlled Fusion 33, 1509 (1991)]. Two distinct varieties of magnetohydrodynamic (MHD) modes are identified, corresponding to a flute-like mode predominantly appearing around the q=1 surface and an outward ballooning mode for q(approximately-greater-than)1. The flute-like modes have nearly equal amplitude on the high-field and low-field side of the magnetic axis, and are mostly observed in moderate performance supershot plasmas with τE〈2τL, while the ballooning-like modes have enhanced amplitude on the low-field side of the magnetic axis and tend to appear in higher performance supershot plasmas with τE(approximately-greater-than)2τL, where τL is the equivalent L-mode confinement time. Both modes appear to propagate in the ion diamagnetic drift direction and are highly localized with radial widths Δr∼5–10 cm, fluctuation levels ñ/n, T˜e/Te〈0.01, and radial displacements ξr∼0.1 cm. Unlike the toroidally localized high-n activity observed just prior to major and minor disruptions on TFTR [E. D. Fredrickson et al., Proceedings of the 15th International Conference on Plasma Physics and Controlled Nuclear Fusion Research, Seville, Spain (International Atomic Energy Agency, Vienna, 1995), No. IAEA-CN-60/A-2-II-5], these modes are typically more benign and may be indicative of MHD activity excited by resonant circulating beam ions. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871887
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  • 7
    Electronic Resource
    Electronic Resource
    Fluctuation measurements in tokamaks with microwave imaging reflectometry : 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. 1955-1961 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: To study the mechanism of anomalous transport in tokamaks requires the use of sophisticated diagnostic tools for the measurement of short-scale turbulent fluctuations. In this article, we describe an attempt at developing a technique capable of providing a comprehensive description of plasma fluctuations with k⊥ρi〈1, such as those driven by the ion temperature gradient mode in tokamaks. The proposed method is based on microwave reflectometry, and stems from a series of numerical calculations showing that the spatial structure of fluctuations near the cutoff could be obtained from the phase of reflected waves when these are collected with a wide aperture optical system forming an image of the cutoff onto an array of phase sensitive detectors. Preliminary measurements with a prototype apparatus on the Torus Experiment for Technology Oriented Research 94 (TEXTOR-94) [U. Samm, Proceedings of the 16th IEEE Symposium on Fusion Engineering, 1995 (IEEE, Piscataway, NJ, 1995), p. 470] confirm the validity of these conclusions. Technical issues in the application of the proposed technique to tokamaks are discussed in this article, and the conceptual design of an imaging reflectometer for the visualization of turbulent fluctuations in the National Spherical Torus Experiment (NSTX) [M. Ono et al., Nucl. Fusion 40, 557 (2000)] is described. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1435564
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  • 8
    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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  • 9
    Electronic Resource
    Electronic Resource
    Observation of particle transport barriers in reverse shear plasmas on the Tokamak Fusion Test Reactor : 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. 1832-1838 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Perturbative experiments on the Tokamak Fusion Test Reactor [Phys. Plasmas 4, 1736 (1997)] (TFTR) have investigated transport in reverse shear plasmas. On TFTR, reverse magnetic shear plasmas bifurcate into two states with different transport properties: reverse shear (RS) and enhanced reverse shear (ERS) with improved core confinement. Measurements of the 14 MeV t(d,n)α neutrons and charge-exchange recombination radiation spectra are used to infer the trace tritium and helium profiles, respectively. The profile evolution indicate the formation of core particle transport barriers in ERS plasmas. The transport barrier is manifested by an order-of-magnitude reduction in the particle diffusivity (DT,DHe) and a smaller reduction in the pinch within the reverse shear region. The low diffusivities are consistent with neoclassical predictions. Furthermore, DT and DHe(approximate)χeff, the effective thermal diffusivity. Although the measured coefficients imply no helium ash accumulation, the situation is uncertain in a reactor due to unknown χeff scaling.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872853
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  • 10
    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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