The Experts below are selected from a list of 300 Experts worldwide ranked by ideXlab platform

Toru Tamagawa - One of the best experts on this subject based on the ideXlab platform.

  • suzaku discovery of the strong radiative recombination continuum of iron from the supernova remnant w49b
    The Astrophysical Journal, 2009
    Co-Authors: Midori Ozawa, Katsuji Koyama, Hiroya Yamaguchi, Kuniaki Masai, Toru Tamagawa
    Abstract:

    We present a hard X-ray spectrum of unprecedented quality of the Galactic supernova remnant (SNR) W49B obtained with the Suzaku satellite. The spectrum exhibits an unusual structure consisting of a saw-edged bump above 8 keV. This bump cannot be explained by any combination of High-Temperature Plasmas in ionization equilibrium. We firmly conclude that this bump is caused by the strong radiative recombination continuum (RRC) of iron, detected for the first time in a SNR. The electron Temperature derived from the bremsstrahlung continuum shape and the slope of the RRC is ~1.5 keV. On the other hand, the ionization Temperature derived from the observed intensity ratios between the RRC and Kα lines of iron is ~2.7 keV. These results indicate that the plasma is in a Highly overionized state. Volume emission measures independently determined from the fluxes of the thermal and RRC components are consistent with each other, suggesting the same origin of these components.

  • suzaku discovery of the strong radiative recombination continuum of iron from the supernova remnant w49b
    arXiv: High Energy Astrophysical Phenomena, 2009
    Co-Authors: Midori Ozawa, Katsuji Koyama, Hiroya Yamaguchi, Kuniaki Masai, Toru Tamagawa
    Abstract:

    We present a hard X-ray spectrum of unprecedented quality of the Galactic supernova remnant W49B obtained with the Suzaku satellite. The spectrum exhibits an unusual structure consisting of a saw-edged bump above 8 keV. This bump cannot be explained by any combination of High-Temperature Plasmas in ionization equilibrium. We firmly conclude that this bump is caused by the strong radiative recombination continuum (RRC) of iron, detected for the first time in a supernova remnant. The electron Temperature derived from the bremsstrahlung continuum shape and the slope of the RRC is 1.5 keV. On the other hand, the ionization Temperature derived from the observed intensity ratios between the RRC and K-alpha lines of iron is 2.7 keV. These results indicate that the plasma is in a Highly overionized state. Volume emission measures independently determined from the fluxes of the thermal and RRC components are consistent with each other, suggesting the same origin of these components.

Midori Ozawa - One of the best experts on this subject based on the ideXlab platform.

  • suzaku discovery of the strong radiative recombination continuum of iron from the supernova remnant w49b
    The Astrophysical Journal, 2009
    Co-Authors: Midori Ozawa, Katsuji Koyama, Hiroya Yamaguchi, Kuniaki Masai, Toru Tamagawa
    Abstract:

    We present a hard X-ray spectrum of unprecedented quality of the Galactic supernova remnant (SNR) W49B obtained with the Suzaku satellite. The spectrum exhibits an unusual structure consisting of a saw-edged bump above 8 keV. This bump cannot be explained by any combination of High-Temperature Plasmas in ionization equilibrium. We firmly conclude that this bump is caused by the strong radiative recombination continuum (RRC) of iron, detected for the first time in a SNR. The electron Temperature derived from the bremsstrahlung continuum shape and the slope of the RRC is ~1.5 keV. On the other hand, the ionization Temperature derived from the observed intensity ratios between the RRC and Kα lines of iron is ~2.7 keV. These results indicate that the plasma is in a Highly overionized state. Volume emission measures independently determined from the fluxes of the thermal and RRC components are consistent with each other, suggesting the same origin of these components.

  • suzaku discovery of the strong radiative recombination continuum of iron from the supernova remnant w49b
    arXiv: High Energy Astrophysical Phenomena, 2009
    Co-Authors: Midori Ozawa, Katsuji Koyama, Hiroya Yamaguchi, Kuniaki Masai, Toru Tamagawa
    Abstract:

    We present a hard X-ray spectrum of unprecedented quality of the Galactic supernova remnant W49B obtained with the Suzaku satellite. The spectrum exhibits an unusual structure consisting of a saw-edged bump above 8 keV. This bump cannot be explained by any combination of High-Temperature Plasmas in ionization equilibrium. We firmly conclude that this bump is caused by the strong radiative recombination continuum (RRC) of iron, detected for the first time in a supernova remnant. The electron Temperature derived from the bremsstrahlung continuum shape and the slope of the RRC is 1.5 keV. On the other hand, the ionization Temperature derived from the observed intensity ratios between the RRC and K-alpha lines of iron is 2.7 keV. These results indicate that the plasma is in a Highly overionized state. Volume emission measures independently determined from the fluxes of the thermal and RRC components are consistent with each other, suggesting the same origin of these components.

M Liniers - One of the best experts on this subject based on the ideXlab platform.

  • moderation of neoclassical impurity accumulation in High Temperature Plasmas of helical devices
    Nuclear Fusion, 2017
    Co-Authors: J L Velasco, Ivan Calvo, S Satake, A Alonso, M Nunami, M Yokoyama, M Sato, T Estrada, J M Fontdecaba, M Liniers
    Abstract:

    Achieving impurity and helium ash control is a crucial issue in the path towards fusion-grade magnetic confinement devices, and this is particularly the case of helical reactors, whose low-collisionality ion-root operation scenarios usually display a negative radial electric field which is expected to cause inwards impurity pinch. In this work we discuss, based on experimental measurements and standard predictions of neoclassical theory, how Plasmas of very low ion collisionality, similar to those observed in the impurity hole of the large helical device (Yoshinuma et al and The LHD Experimental Group 2009 Nucl. Fusion 49 062002, Ida et al and The LHD Experimental Group 2009 Phys. Plasmas 16 056111 and Yokoyama et al and LHD Experimental Group 2002 Nucl. Fusion 42 143), can be an exception to this general rule, and how a negative radial electric field can coexist with an outward impurity flux. This interpretation is supported by comparison with documented discharges available in the International Stellarator-Heliotron Profile Database, and it can be extrapolated to show that achievement of High ion Temperature in the core of helical devices is not fundamentally incompatible with low core impurity content.

  • moderation of neoclassical impurity accumulation in High Temperature Plasmas of helical devices
    arXiv: Plasma Physics, 2016
    Co-Authors: J L Velasco, Ivan Calvo, S Satake, A Alonso, M Nunami, M Yokoyama, M Sato, T Estrada, J M Fontdecaba, M Liniers
    Abstract:

    Achieving impurity and helium ash control is a crucial issue in the path towards fusion-grade magnetic confinement devices, and this is particularly the case of helical reactors, whose low-collisionality ion-root operation scenarios usually display a negative radial electric field which is expected to cause inwards impurity pinch. In these work we discuss, based on experimental measurements and standard predictions of neoclassical theory, how Plasmas of very low ion collisionality, similar to those observed in the impurity hole of the Large Helical Device, can be an exception to this general rule, and how a negative radial electric field can coexist with an outward impurity flux. This interpretation is supported by comparison with documented discharges available in the International Stellarator-Heliotron Profile Database, and it can be extrapolated to show that achievement of High ion Temperature in the core of helical devices is not fundamentally incompatible with low core impurity content.

M H R Hutchinson - One of the best experts on this subject based on the ideXlab platform.

  • time resolved study of nonlocal electron heat transport in High Temperature Plasmas
    Physical Review Letters, 1998
    Co-Authors: T Ditmire, E T Gumbrell, R A Smith, A Djaoui, M H R Hutchinson
    Abstract:

    Exploiting the High absorption efficiency of intense, ultrashort laser pulses in gases of atomic clusters we have created plasma filaments with Temperatures of $g1\mathrm{keV}$ and electron densities in excess of ${10}^{20}{\mathrm{cm}}^{\ensuremath{-}3}$. Using picosecond laser pulses, we have interferometrically measured the temporal and spatial evolution of the electron density in these Plasmas on a fast $(l50\mathrm{ps})$ time scale. Our measurements indicate that nonlocal heat transport by hot electrons drives a fast ionization wave, and the data agree well with a nonlocal heat transport model.

S Kubo - One of the best experts on this subject based on the ideXlab platform.

  • extension of operational regime in High Temperature Plasmas and effect of ecrh on ion thermal transport in the lhd
    Nuclear Fusion, 2017
    Co-Authors: H Takahashi, Kenichi Nagaoka, S Murakami, M Osakabe, H Nakano, T I Tsujimura, S Kubo, T Kobayashi, K Tanaka, R Seki
    Abstract:

    A simultaneous High ion Temperature (T i) and High electron Temperature (T e) regime was successfully extended due to an optimized heating scenario in the LHD. Such High-Temperature Plasmas were realized by the simultaneous formation of an electron internal transport barrier (ITB) and an ion ITB by the combination of High power NBI and ECRH. Although the ion thermal confinement was degraded in the plasma core with an increase of T e/T i by the on-axis ECRH, it was found that the ion thermal confinement was improved at the plasma edge. The normalized ion thermal diffusivity at the plasma edge was reduced by 70%. The improvement of the ion thermal confinement at the edge led to an increase in T i in the entire plasma region, even though the core transport was degraded.

  • impact of nonlocal electron heat transport on the High Temperature Plasmas of lhd
    Nuclear Fusion, 2007
    Co-Authors: Nobumichi Tamura, K Ida, R Sakamoto, S Kubo, K Tanaka, S Inagaki, Clive Michael, T Tokuzawa, T Shimozuma, K Itoh
    Abstract:

    Edge cooling experiments with a tracer-encapsulated solid pellet in the large helical device (LHD) show a significant rise in core electron Temperature (the maximum rise is around 1 keV) as well as in many tokamaks. This experimental result indicates the possible presence of the nonlocality of electron heat transport in Plasmas where turbulence as a cause of anomalous transport dominates. The nonlocal electron Temperature rise in the LHD takes place in almost the same parametric domain (e.g. in a low density) as in the tokamaks. Meanwhile, the experimental results of LHD show some new aspects of nonlocal electron Temperature rise, for example the delay in the nonlocal rise of core electron Temperature relative to the pellet penetration time increases with the increase both in the collisionality in the core plasma and the electron Temperature gradient scale length in the outer region of the plasma.

  • thirty minute plasma sustainment by real time magnetic axis swing for effective divertor load dispersion in the large helical device
    Physics of Plasmas, 2006
    Co-Authors: T Mutoh, S Kubo, Y Takeiri, T Shimozuma, S Masuzaki, R Kumazawa, T Seki, Kenji Saito, Y Nakamura, Y Yoshimura
    Abstract:

    Achieving steady-state plasma operation at High plasma Temperatures is one of the important goals of worldwide magnetic fusion research. A High Temperature of approximately 2keV, and steady-state plasma-sustainment operation of the Large Helical Device (LHD) [O. Motojima, K. Akaishi, H. Chikaraishi et al., Nucl. Fusion 40, 599 (2000)] is reported. High-Temperature Plasmas were created and maintained for more than 30min with a world record injected heating power of 1.3GJ. The three-dimensional heat-deposition profile of the LHD helical divertor was modified and during long-pulse discharges it effectively dispersed the heat load using a magnetic-axis swing technique developed at the LHD. A sweep of only 3cm of the major radius of the magnetic axis position (less than 1% of the major radius of the LHD) was enough to disperse the divertor heat load. The modification of the heat-load profile was explained well by field-line tracing. The steady-state plasma was heated and sustained mainly by hydrogen minority i...