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  • 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
    Ion heat pulse after a sawtooth crash in the JAERI Fusion Torus-2M tokamak (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 3696-3700 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The ion heat pulse after a sawtooth crash is studied by a time-of-flight (TOF) neutral measurement. A rapid change of the bulk ion energy distribution near the edge is observed after a sawtooth crash. The delay time is measured, and the effective measuring position is estimated by a neutral transport code. Then a transient ion thermal conductivity, χiHP, of about (7–18) m2/s is evaluated for the low confinement mode (L-mode) plasma. The simple diffusive model with constant χiHP, however, does not explain the amplitude of the pulse in the ion energy distribution. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872029
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  • 3
    Electronic Resource
    Electronic Resource
    Self-sustained plasma turbulence due to current diffusion (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 4140-4148 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Plasma turbulence and anomalous transport by the electrostatic current diffusive interchange mode are studied by the nonlinear simulation based on the magnetohydrodynamic model. The turbulence is found to have a typical characteristic of subcritical turbulence. The saturation level, as a function of the pressure gradient ∇p, is confirmed to scale like ||∇p||3/2. This nature holds independent of the ratio ||∇p||/||∇pc|| where ||∇pc||, is a critical pressure gradient against linear instability. The turbulence-driven transport is also evaluated. The simulation result confirms the theoretical prediction, which is based on the self-sustained turbulence, with respect to the nonlinear growth and damping. Both the normal cascade and inverse cascade are essential in establishing the stationary turbulent state. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871038
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  • 4
    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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  • 5
    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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  • 6
    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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  • 7
    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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  • 8
    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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  • 9
    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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  • 10
    Electronic Resource
    Electronic Resource
    Numerical study of chaos based on a shell model (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Chaos 9 (1999), S. 393-402 
    Details
    ISSN: 1089-7682
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A shell model is introduced to study a turbulence driven by the thermal instability (Rayleigh–Bénard convection). This model equation describes cascade and chaos in the strong turbulence with high Rayleigh number. The chaos is numerically studied based on this model. The characteristics of the turbulence are analyzed and compared with those of the Gledzer–Ohkitani–Yamada (GOY) model. Quantities such as a mean value of total fluctuation energy, it's standard deviation, time averaged wave spectrum, probability distribution function, frequency spectrum, the maximum instantaneous Lyapunov exponent, distribution of instantaneous Lyapunov exponents, are evaluated. The dependences of these quantities on the error of numerical integration are also examined. There is not a clear correlation between the numerical accuracy and the accuracy of these quantities, since the interaction between a truncation error and an intrinsic nonlinearity of the system exists. A finding is that the maximum Lyapunov exponent is insensitive to a truncation error. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.166416
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