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  • 2000-2004  (8)
  • 1990-1994  (16)
  • 1970-1974  (4)
  • 1
    Electronic Resource
    Electronic Resource
    Neutron depolarization in reentrant spin glasses Ni1−xMnx (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 5232-5234 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Polarization analysis of the transmitted beam was performed using a pulsed neutron source in a reentrant spin-glass (RSG) system Ni1−xMnx, for a concentration range (0.23≤x≤0.28) encompassing the critical concentration. The same samples were previously used to determine the magnetic phase diagram by magnetization measurements. The polarization P was measured as a function of temperature (15≤T≤300 K), neutron wavelength (3≤λ≤10 A(ring)) and applied field (7 Oe≤H≤125 Oe). Unlike other RSG systems, P measured in a 7 Oe field decreases at all temperatures below the Curie temperature even for the samples close to the critical concentration. The wavelength dependence of the polarization indicates the existence of magnetic domains whose size δ decreases with increasing x from a few tenths of micrometers at x=0.23 to a few thousands of angströms at x=0.25. No depolarization occurs for x〉0.25. As shown for x=0.23, the irreversibilities of the polarization, which depends on the cooling conditions, indicate that the domain arrangement freezes at low temperature. Clearly, in NiMn, the drop of the susceptibility at low temperature does not result from a decrease of the size or magnetization of the domains but from a slowing down of their mobility.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.344620
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  • 2
    Electronic Resource
    Electronic Resource
    Experimental study of the bifurcation nature of the electrostatic potential of a toroidal helical plasma (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 4152-4183 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The bifurcation nature of the electrostatic structure is studied in the toroidal helical plasma of the Compact Helical System (CHS) [K. Matsuoka et al., Proceedings of the 12th International Conference on Plasma Physics and Controlled Nuclear Fusion Research, Nice, 1988 (International Atomic Energy Agency, Vienna, 1989), Vol. 2, p. 411]. Observation of bifurcation-related phenomena is introduced, such as characteristic patterns of discrete potential profiles, and various patterns of self-sustained oscillations termed electric pulsation. Some patterns of the electrostatic structure are found to be quite important for fusion application owing to their association with transport barrier formation. It is confirmed, as is shown in several tokamak experiments, that the thermal transport barrier is linked with electrostatic structure through the radial electric field shear that can reduce the fluctuation resulting in anomalous transport. This article describes in detail spatio-temporal evolution during self-sustained oscillation, together with correlation between the radial electric field and other plasma parameters. An experimental survey to find dependence of the temporal and spatial patterns on plasma parameters is performed in order to understand systematically the bifurcation property of the toroidal helical plasma. The experimental results are compared with the neoclassical bifurcation property that is believed to explain the observed bifurcation property of the CHS plasmas. The present results show that the electrostatic property plays an essential role in the structural formation of toroidal helical plasmas, and demonstrate that toroidal plasma is an open system with a strong nonlinearity to provide a new attractive problem to be studied. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1290483
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  • 3
    Electronic Resource
    Electronic Resource
    Partition in power transfer and dissipation rate in self-sustained turbulence (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 1154-1158 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Power partition and energy dissipation rates are examined for a self-sustained stationary turbulence of a high-n ballooning mode in a tokamak plasma. It is found that the power to excite fluctuations is almost equally transferred to perpendicular ion motion and to parallel electron motion. The ratio of the thermalized power, which excites and sustains the turbulence, to the total power lost by energy diffusion is found to be of the order of the broken symmetry parameter, i.e., the inverse aspect ratio, a/R. The dissipation rates of the fluctuations due to the thermal conductivity, the electron viscosity, and the ion viscosity are also calculated separately. The dissipation is dominated by that associated with the thermal conductivity. The relation between the induced global flux and the microscopic dissipation is also derived. It is found that a fractional part of order a/R of the dissipated power is effective in sustaining the turbulent modes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870711
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  • 4
    Electronic Resource
    Electronic Resource
    Thickness of the layer of high shear radial electric field in JFT-2M H-mode plasmas (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 116-119 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The poloidal rotation velocity profiles both in low-confinement (L) and high-confinement (H) mode measured in JAERI Fusion Torus 2 Modified (JFT-2M) [Phys. Rev. Lett. 65, 1364 (1990)] are compared with H-mode models based on ion orbit loss. The profiles of poloidal rotation velocity measured in L and H modes are consistent with the calculation which consists of ion orbit loss model. The observed dependence of the thickness of the layer of high shear Er on poloidal gyroradius is explained by the radial transport of poloidal rotation velocity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870944
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  • 5
    Electronic Resource
    Electronic Resource
    Transition in multiple-scale-lengths turbulence in plasmas : 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. 1947-1954 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The statistical theory of strong turbulence in inhomogeneous plasmas is developed for the cases where fluctuations with different scale lengths coexist. Statistical nonlinear interactions between semimicro and micro modes are first kept in the analysis as the drag, noise and drive. The nonlinear dynamics determines both the fluctuation levels and the cross field turbulent transport for the fixed global parameters. A quenching or suppressing effect is induced by their nonlinear interplay, even if both modes are unstable when analyzed independently. Influence of the inhomogeneous global radial electric field is discussed. A new insight is given for the physics of the internal transport barrier. The thermal fluctuation of the scale length of λD is assumed to be statistically independent. The hierarchical structure is constructed according to the scale lengths. Transitions in turbulence are found and phase diagrams with cusp type catastrophe are obtained. Dynamics is followed. Statistical properties of the subcritical excitation are discussed. The probability density function (PDF) and transition probability are obtained. Power laws are obtained in the PDF as well as in the transition probability. Generalization for the case where turbulence is composed of three classes of modes is also developed. A new catastrophe of turbulent states is obtained. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1455005
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  • 6
    Electronic Resource
    Electronic Resource
    Ion cyclotron range of frequency heating experiments on the large helical device and high energy ion behavior : 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. 2139-2147 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ion cyclotron range of frequency (ICRF) heating experiments on the Large Helical Device (LHD) [O. Motojima et al. Fus. Eng. Des. 20, 3 (1993)] achieved significant advances during the third experimental campaign carried out in 1999. They showed significant results in two heating modes; these are modes of the ICH-sustained plasma with large plasma stored energy and the neutral beam injection (NBI) plasma under additional heating. A long-pulse operation of more than 1 minute was achieved at a level of 1 MW. The characteristics of the ICRF heated plasma are the same as those of the NBI heated plasma. The energy confinement time is longer than that of International Stellarator Scaling 95. Three keys to successful ICRF heating are as follows: (1) an increase in the magnetic field strength, (2) the employment of an inward shift of the magnetic axis, (3) the installation of actively cooled graphite plates along the divertor legs. Highly energetic protons accelerated by the ICRF electric field were experimentally observed in the energy range from 30 to 250 keV and the tail temperature depended on the energy balance between the wave heating and the electron drag. The transfer efficiency from the high energy ions to the bulk plasma was deduced from the increase in the energy confinement time due to the high energy ions in the lower density discharge, which agrees fairly well with the result obtained by the Monte Carlo simulation. The transfer efficiency is expected to be 95% at an electron density of more than ne=5.0×1019 m−3 even in the high power heating of 10 MW. The accumulation of impurities, e.g., FeXVI and OV was not observed in high rf power and long pulse operation. The well-defined divertor intrinsic to LHD is believed to be useful in reducing the impurity influx. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1354152
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  • 7
    Electronic Resource
    Electronic Resource
    Thermal and electric oscillation driven by orbit loss in helical systems (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 796-798 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Coupled oscillation of the radial electric field, the heating power, and the plasma temperature in helical systems is analyzed. This oscillation is caused by the influence of the radial electric field on the direct loss of injected fast ions. The damped oscillations of the radial electric field, temperature and fast-ion loss are predicted. Conditions for the occurrence of the mode and the oscillation frequency are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870774
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  • 8
    Electronic Resource
    Electronic Resource
    A compact neutron counter telescope with thick radiator (COTETRA) for fusion experiments (1994)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 65 (1994), S. 1636-1643 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A new type of neutron spectrometer, which is called COTETRA (counter telescope with thick radiator), has been developed for diagnosing DT fusion plasma. It is based on the recoil proton measurement and has such advantages as: (1) direct measurement of the neutron energy without the unfolding procedure, (2) sufficiently fine energy resolution and high detection efficiency for 14 MeV neutrons, (3) wide dynamic range of counting rate, and (4) good n–γ discrimination. A prototype of COTETRA was constructed and tested using a DT neutron accelerator. The energy resolution of 5.3%±0.9% was obtained for 14 MeV neutron with the detection efficiency of 1.3×10−4 [counts/(n/cm2)]. A Monte Carlo simulation code was developed and the performances of COTETRA were examined. The calculation agrees with the results of the experiment within its margin of error and suggests that energy resolution up to 3% with a detection efficiency of 10−5 [counts/(n/cm2)] could be achieved if the condition of the radiator could be successfully adjusted.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1144852
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  • 9
    Electronic Resource
    Electronic Resource
    Rapid thermal oxidation of thin nitride dielectrics deposited on rapid thermal nitrided polycrystalline silicon (1992)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 61 (1992), S. 1313-1315 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This letter compares the effects of two different oxidation techniques, i.e., rapid thermal and conventional wet (steam) oxidations, on the dielectric breakdown and charge trapping characteristics of thin Si3N4 films deposited on rapid thermally nitrided polycrystalline silicon. Results show that, in addition to the low thermal budget, rapid-thermal-oxidized Si3N4 shows superior time-dependent dielectric breakdown characteristics in terms of reduced defect densities and improved film intrinsic properties. Compared to wet-oxidized dielectrics, suppressed charge trapping is observed for rapid-thermal-oxidized Si3N4 stacked dielectrics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.107576
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  • 10
    Electronic Resource
    Electronic Resource
    Theory of pseudoclassical confinement and transition to L mode (1993)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 3299-3303 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A theory of the self-sustained turbulence is developed for resistive plasma in toroidal devices. Pseudoclassical confinement is obtained in the low-temperature limit. As temperature increases, the current diffusivity prevails upon resistivity, and the turbulence nature changes so as to recover the L-mode transport. Comparison with experimental observation on this transition is made. The Hartmann number is also given.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860626
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