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  • 1
    Electronic Resource
    Electronic Resource
    Experimental test of the radial force balance equation in the compact helical system (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 1-4 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Experimental test of the radial force balance equation was done in the Compact Helical System Heliotron/Torsatron [S. Okamura et al. Nucl. Fusion 39, 1337 (1999)]. A radial electric field is measured with a heavy ion beam probe, while plasma rotation and drift velocity of fully ionized carbon are measured with charge exchange spectroscopy. The two measurements agree with each other to within 10% of the radial electric field in a wide range of electron densities of 0.3–2.0×1019 m−3. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1331097
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  • 2
    Electronic Resource
    Electronic Resource
    Electron cyclotron resonance heating near the turning point in inhomogeneous magnetic field (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 3318-3323 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Cyclotron resonance heating of electrons in a magnetic beach is studied by rigorous numerical analysis of the electron trajectories. It is confirmed that a heating response function [Y. Kiwamoto et al., Phys. Plasmas 1 834 (1994)] connecting the velocity distributions in both sides of the resonance layer can be applied over a wider range of electron velocities than originally expected. For electrons mirror-reflected close to the resonance layer, however, the electron velocity distribution after heating substantially deviates from the prediction of the response function. The deviation is quantitatively evaluated to obtain a criterion of applicability of the response function. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871600
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  • 3
    Electronic Resource
    Electronic Resource
    Contribution of Yushmanov-trapped electrons to a thermal dike (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 1603-1611 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A substantial amount of Yushmanov-trapped electrons are generated as a result of electron cyclotron resonance heating employed for generating a thermal dike in an open magnetic field configuration. The production rate and the energy spectrum of the trapped electrons are calculated by using a heating response function. The calculated energy spectrum of the end-loss electrons driven from the Yushmanov-trapped region indicates a reduction in power efficiency of the thermal dike. The potential profile modified by the Yushmanov-trapped particles tends to reduce their production rate, leading to a stationary state. Their significance to a thermal dike basic experiment in the end region of the GAMMA 10 tandem mirror [Plasma Physics and Controlled Nuclear Fusion Research 1992 (International Atomic Energy Agency, Vienna, 1993), Vol. 2, p. 651] is discussed. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872019
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  • 4
    Electronic Resource
    Electronic Resource
    Suppression of secondary electrons from an endplate of a tandem mirror by use of a biased mesh (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 352-354 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Negative bias is applied to a mesh placed in front of an endplate of the GAMMA 10 tandem mirror [Phys. Rev. Lett. 55, 939 (1985)]. A bias voltage of around 10 V results in an increase of the potential difference by an order of kV in the end region. The increment is about two times the temperature of end-loss electrons and most of that stems from the sheath potential drop in front of the endplate. Provided that almost all the secondary electrons emitted from endplate are reflected, these results agree with the prediction of a potential model for the open magnetic field configuration [J. Phys Soc. Jpn. 61, 3153 (1992)]. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871439
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  • 5
    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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  • 6
    Electronic Resource
    Electronic Resource
    Inward turbulent particle transport in a helical plasma heated by neutral beam injection (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 4035-4041 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In neutral-beam-injection (NBI) heated plasmas of the Compact Helical System (CHS) heliotron/torsatron [K. Matsuoka et al., Plasma Physics and Controlled Nuclear Fusion Research, 1988 (International Atomic Energy Agency, Vienna, 1989), Vol. 2, p. 441], inward turbulent particle flux is observed at a particular radial location near the plasma edge. The observed reversal of the particle flux is connected to the change in the cross-phase between electron density and poloidal electric field fluctuations. This phenomenon is observed in the parameter regime of low collisionality at the electron temperature Te〉15 eV, electron density ne〈3×1018 m−3, which approximately corresponds to the effective collision frequency normalized by the transit frequency of a circulating particle ν*(approximately-less-than)1. The large inward particle flux ((approximately-greater-than)1×1020 m−2 s−1) correlates with the positive shear of the radial electric field Er′ ((approximately-greater-than)1×106 V m−2), but does not have clear correlation with the radial electric field Er and the curvature Er″. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1387267
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  • 7
    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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  • 8
    Electronic Resource
    Electronic Resource
    Use of a semiconductor detector for measurement of high energy end loss ions from a tandem mirror (1997)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 1433-1437 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A semiconductor detector is applied for measurement of high energy end loss ions (E≥15 keV) from a tandem mirror. Its energy sensitivity to protons calibrated by using a monochromatic ion source is found to be the same as that to electrons. The semiconductor detector is installed on an end wall of the GAMMA 10 tandem mirror and high energy end loss ions are observed with the detector when ions in the confinement region are strongly heated by ion cyclotron waves. Counts of high energy end loss ions are closely related with a diamagnetic signal representing ion heating. The energy of the end loss ions spreads with time and attains to 50–60 keV. Time behavior of the ion count suggests that unknown loss processes other than classical Coulomb scattering are relevant to ion end loss. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147629
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  • 9
    Electronic Resource
    Electronic Resource
    Current–voltage characteristics of the end loss ion flux from a tandem mirror collected on a gridded energy analyzer (1996)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 67 (1996), S. 2207-2214 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Examination is made of the relation between the distribution function of the ions confined in a tandem mirror and the current–voltage (I–V) characteristics of the end loss ions collected on a gridded energy analyzer. To do this, a model ion distribution function characterized by two parameters, an anisotropy parameter χ and a decay parameter Y is used. The decay parameter represents depletion of ion distribution in the loss cone. A Maxwellian distribution as the limit of Y=∞ is shown not to reproduce the measured I–V curve as an energy spectrum of the ions lost from the central cell of the GAMMA 10 tandem mirror [Phys. Rev. Lett. 55, 939 (1985)]. The ions in the central cell are subject to strong ICRH and have a highly anisotropic velocity distribution. These ions are deeply trapped in the central cell and the loss cone is not fully occupied. The model distribution with a small value of Y represents such features of the ion distribution. From comparison between a measured loss current and calculated one, the decay parameter of the model distribution function is roughly determined. The model distribution with this parameter yields I–V characteristics similar to the measured one. The present article gives the relation between the apparent ion temperature Ti simply determined from the slope of the log plot of the measured I–V curve and the real parallel ion temperature Ti(parallel). When the ion distribution is of a loss cone type, Ti is almost equal to Ti(parallel). On the other hand, Ti can be more than two times as high as Ti(parallel) if the ion distribution is Maxwellian-like. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147038
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  • 10
    Electronic Resource
    Electronic Resource
    Performance of a materials science facility at the Photon Factory: Soft x-ray beamline BL 13C coupled with multipurpose analytical apparatus : Proceedings of the 5th international conference on synchrotron radiation instrumentation (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 1780-1782 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The performance data of an undulator soft x-ray beamline based on the cylindrical element monochromator concept are described. Photon fluxes over 1012 photon/s 0.1% b.w. are achieved with the slit width of 100 μm at the harmonic peaks of a 13-period undulator. The maximum resolution obtained at the N K edge (E/ΔE) is ≈5000 with the slit width of 10 μm. The beamline is equipped with a multipurpose analytical instrument having a hemispherical electron analyzer and other detectors. The system is used for both x-ray photoelectron spectroscopy and x-ray absorption fine structure analyses for surface and materials science. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1145848
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