Y. Sakamoto

Tohoku Gakuin University, Japan

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Publications (360)605.22 Total impact

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    ABSTRACT: In this paper, recent progress on experimental analysis and theoretical models for non-local transport (non-Fickian fluxes in real space) is reviewed. The non-locality in the heat and momentum transport observed in the plasma, the departures from linear flux-gradient proportionality, and externally triggered non-local transport phenomena are described in both L-mode and improved-mode plasmas. Ongoing evaluation of ‘fast front’ and ‘intrinsically non-local’ models, and their success in comparisons with experimental data, are discussed
    Nuclear Fusion 01/2015; 55(1):013022. DOI:10.1088/0029-5515/55/1/013022 · 3.24 Impact Factor
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    ABSTRACT: We describe a muon track reconstruction algorithm for the reactor anti-neutrino experiment Double Chooz. The Double Chooz detector consists of two optically isolated volumes of liquid scintillator viewed by PMTs, and an Outer Veto above these made of crossed scintillator strips. Muons are reconstructed by their Outer Veto hit positions along with timing information from the other two detector volumes. All muons are fit under the hypothesis that they are through-going and ultrarelativistic. If the energy depositions suggest that the muon may have stopped, the reconstruction fits also for this hypothesis and chooses between the two via the relative goodness-of-fit. In the ideal case of a through-going muon intersecting the center of the detector, the resolution is ~40 mm in each transverse dimension. High quality muon reconstruction is an important tool for reducing the impact of the cosmogenic isotope background in Double Chooz.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 11/2014; 764:330-339. DOI:10.1016/j.nima.2014.07.058 · 1.32 Impact Factor
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    ABSTRACT: The energy spectra of neutrons were measured by a time-of-flight method for 120 GeV protons on thick graphite, aluminum, copper, and tungsten targets with an NE213 scintillator at the Fermilab Test Beam Facility. Neutron energy spectra were obtained between 25 and 3000 MeV at emission angles of 30°, 45°, 120°, and 150°. The spectra were parameterized as neutron emissions from three moving sources and then compared with theoretical spectra calculated by PHITS and FLUKA codes. The yields of the theoretical spectra were substantially underestimated compared with the yields of measured spectra. The integrated neutron yields from 25 to 3000 MeV calculated with PHITS code were 16–36% of the experimental yields and those calculated with FLUKA code were 26–57% of the experimental yields for all targets and emission angles.
    Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms 10/2014; 337:68–77. DOI:10.1016/j.nimb.2014.07.019 · 1.12 Impact Factor
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    ABSTRACT: Relations between a net electrical output power and dimensions of components in radial build are investigated based on the ITER plasma performance to develop a conceptual design of DEMO with the net electrical output power of several hundred MW. Reducing the dimensions of in-vessel components and increasing the thickness of the toroidal field coil contribute to strengthen the toroidal magnetic field at plasma, which brings about increase in a net electrical output power. The relation between the minimum plasma major radius and the maximum net electrical output power is clarified. Furthermore effects of improvements in the ITER plasma performance on the net electricity are also analyzed; indicating the increase of normalized beta could have advantage from the viewpoint of the divertor heat load because the increase of synchrotron radiation loss power contributes to reduce the divertor heat load, though the higher energy confinement is required.
    Nuclear Engineering and Design Fusion 10/2014; 89(9-10). DOI:10.1016/j.fusengdes.2014.04.032
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    ABSTRACT: After the Fukushima Dai-ichi nuclear accident, a need for assuring safety of fusion energy has grown in the Japanese (JA) fusion research community. DEMO safety research has been launched as a part of Broader Approach DEMO Design Activities (BA-DDA). This paper reports progress in the fusion DEMO safety research conducted under BA-DDA. Safety requirements and evaluation guidelines have been, first of all, established based on those established in the Japanese ITER site invitation activities. The radioactive source terms and energies that can mobilize such source terms have been assessed for a reference DEMO concept. This concept employs in-vessel components that are cooled by pressurized water and built of a low activation ferritic steel (F82H), contains solid pebble beds made of lithium-titanate (Li2TiO3) and beryllium–titanium (Be12Ti) for tritium breeding and neutron multiplication, respectively. It is shown that unlike the energies expected in ITER, the enthalpy in the first wall/blanket cooling loops is large compared to the other energies expected in the reference DEMO concept. Reference accident event sequences in the reference DEMO in this study have been analyzed based on the Master Logic Diagram and Functional Failure Mode and Effect Analysis techniques. Accident events of particular concern in the DEMO have been selected based on the event sequence analysis and the hazard assessment.
    Fusion Engineering and Design 10/2014; 89(9-10). DOI:10.1016/j.fusengdes.2014.04.062 · 1.15 Impact Factor
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    ABSTRACT: The oscillation results published by the Double Chooz collaboration in 2011 and 2012 rely on background models substantiated by reactor-on data. In this analysis, we present a background-model-independent measurement of the mixing angle $\theta_{13}$ by including 7.53 days of reactor-off data. A global fit of the observed neutrino rates for different reactor power conditions is performed, yielding a measurement of both $\theta_{13}$ and the total background rate. The results on the mixing angle are improved significantly by including the reactor-off data in the fit, as it provides a direct measurement of the total background rate. This reactor rate modulation analysis considers antineutrino candidates with neutron captures on both Gd and H, whose combination yields $\sin^2(2\theta_{13})=$ 0.102 $\pm$ 0.028(stat.) $\pm$ 0.033(syst.). The results presented in this study are fully consistent with the ones already published by Double Chooz, achieving a competitive precision. They provide, for the first time, a determination of $\theta_{13}$ that does not depend on a background model.
    Physics Letters B 07/2014; 735:51-56. DOI:10.1016/j.physletb.2014.04.045 · 6.02 Impact Factor
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    ABSTRACT: The Double Chooz experiment measures the neutrino mixing angle θ 13 by detecting reactor \( {\overline{\nu}}_e \) via inverse beta decay. The positron-neutron space and time coincidence allows for a sizable background rejection, nonetheless liquid scintillator detectors would profit from a positron/electron discrimination, if feasible in large detector, to suppress the remaining background. Standard particle identification, based on particle dependent time profile of photon emission in liquid scintillator, can not be used given the identical mass of the two particles. However, the positron annihilation is sometimes delayed by the ortho-positronium (o-Ps) metastable state formation, which induces a pulse shape distortion that could be used for positron identification. In this paper we report on the first observation of positronium formation in a large liquid scintillator detector based on pulse shape analysis of single events. The o-Ps formation fraction and its lifetime were measured, finding the values of 44 % ±12 % (sys.) ±5 % (stat.) and 3.68 ns ±0.17 ns (sys.) ±0.15 ns (stat.) respectively, in agreement with the results obtained with a dedicated positron annihilation lifetime spectroscopy setup.
    Journal of High Energy Physics 07/2014; DOI:10.1007/JHEP10(2014)032 · 5.62 Impact Factor
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    ABSTRACT: The Double Chooz experiment presents improved measurements of the neutrino mixing angle θ 13 using the data collected in 467.90 live days from a detector positioned at an average distance of 1050 m from two reactor cores at the Chooz nuclear power plant. Several novel techniques have been developed to achieve significant reductions of the backgrounds and systematic uncertainties with respect to previous publications, whereas the efficiency of the \( {\overline{\nu}}_e \) signal has increased. The value of θ 13 is measured to be sin2 2θ 13 = 0.090 − 0.029+ 0.032 from a fit to the observed energy spectrum. Deviations from the reactor \( {\overline{\nu}}_e \) prediction observed above a prompt signal energy of 4 MeV and possible explanations are also reported. A consistent value of θ 13 is obtained from a fit to the observed rate as a function of the reactor power independently of the spectrum shape and background estimation, demonstrating the robustness of the θ 13 measurement despite the observed distortion.
    Journal of High Energy Physics 06/2014; DOI:10.1007/JHEP10(2014)086 · 5.62 Impact Factor
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    ABSTRACT: In our previous study, double and mirror symmetric activation peaks found for Al and Au arranged spatially on the back of the Hadron absorber of the NuMI beamline in Fermi lab were considerably higher than those expected purely from muon-induced reactions. From material activation benchmark experiments, we conclude that this activation is due to hadrons with energy greater than 3 GeV that had passed downstream through small gaps in the hadron absorber.
    Nuclear Data Sheets 06/2014; 120:219-221. DOI:10.1016/j.nds.2014.07.051 · 3.35 Impact Factor
  • Proceedings of the 12th Asia Pacific Physics Conference (APPC12); 03/2014
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    ABSTRACT: The irradiation hardening behavior of reduced-activation ferritic steels after single Fe-ion beam irradiation and dual-ion (Fe ion and He ion) beam irradiation experiments was investigated with nanoindentation tests. The ion-irradiation experiments were conducted at 563 K with 6.4 MeV Fe3+ ions up to 3 dpa at a 600 nm depth from the irradiated surface. Furthermore, these experiments were conducted with and without simultaneous energy-degraded 1 MeV He+ ions up to 300 appm. The materials used were F82H, F82H + 1Ni, and F82H + 2Ni to investigate the effect of Ni addition on the irradiation hardening behavior. The measured nanoindentation hardness was converted to the bulk-equivalent hardness based on a combination of the Nix-Gao model to explain the indentation size effect and the composite hardness model to explain the softer substrate effect of the nonirradiated region beyond the irradiated depth range. It is clearly shown that the Ni addition enhances the irradiation hardening of F82H. The bulk-equivalent hardness is compared with the experimentally obtained Vickers hardness of F82H steels after neutron irradiation. The effect of simultaneously implanted helium on the irradiation hardening is negligible in the investigated irradiation conditions.
    Journal of Nuclear Materials 11/2013; 442(1-3):23-. DOI:10.1016/j.jnucmat.2012.12.033 · 2.02 Impact Factor
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    ABSTRACT: The total cross section has been measured for ω meson photoproduction on the proton for the center-of-mass energy ${\sqrt{s}}$ ranging from 1.69 to 1.75 GeV. Including the subthreshold region of ω photoproduction, a set of about 40 data points has been obtained with a fine energy step of 1–2 MeV. The data set enables us to deduce the ω-N scattering length.
    Few-Body Systems 08/2013; 54(7-10). DOI:10.1007/s00601-013-0658-5 · 1.51 Impact Factor
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    ABSTRACT: Baryon spectroscopy is important to understand Quantum Chromodynamics at low energies. In this purpose, a series of π 0 and η photoproduction experiments was carried out with an electro-magnetic calorimeter FOREST at Research Center for Electron Photon Science, Tohoku University. The incident tagged bremsstrahlung photon energy ranges from 550 to 1,150 MeV. The differential and total cross sections obtained for π 0 and η photoproduction processes on the proton are consistent with the SAID and MAID calculations. The analysis of π 0 and η photoproduction on the neutron is underway.
    Few-Body Systems 08/2013; 54(7-10). DOI:10.1007/s00601-013-0676-3 · 1.51 Impact Factor
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    ABSTRACT: The Double Chooz experiment has determined the value of the neutrino oscillation parameter $\theta_{13}$ from an analysis of inverse beta decay interactions with neutron capture on hydrogen. This analysis uses a three times larger fiducial volume than the standard Double Chooz assessment, which is restricted to a region doped with gadolinium (Gd), yielding an exposure of 113.1 GW-ton-years. The data sample used in this analysis is distinct from that of the Gd analysis, and the systematic uncertainties are also largely independent, with some exceptions, such as the reactor neutrino flux prediction. A combined rate- and energy-dependent fit finds $\sin^2 2\theta_{13}=0.097\pm 0.034(stat.) \pm 0.034 (syst.)$, excluding the no-oscillation hypothesis at 2.0 \sigma. This result is consistent with previous measurements of $\sin^2 2\theta_{13}$.
    Physics Letters B 06/2013; 723(1-3):66-70. DOI:10.1016/j.physletb.2013.04.050 · 6.02 Impact Factor
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    ABSTRACT: Double Chooz is unique among modern reactor-based neutrino experiments studying ν̅ e disappearance in that data can be collected with all reactors off. In this paper, we present data from 7.53 days of reactor-off running. Applying the same selection criteria as used in the Double Chooz reactor-on oscillation analysis, a measured background rate of 1.0±0.4 events/day is obtained. The background model for accidentals, cosmogenic β-n-emitting isotopes, fast neutrons from cosmic muons, and stopped-μ decays used in the oscillation analysis is demonstrated to be correct within the uncertainties. Kinematic distributions of the events, which are dominantly cosmic-ray-produced correlated-background events, are provided. The background rates are scaled to the shielding depths of two other reactor-based oscillation experiments, Daya Bay and RENO.
    Physical Review D 01/2013; 87(1):011102. DOI:10.1103/PhysRevD.87.011102 · 4.86 Impact Factor
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    ABSTRACT: We present a search for Lorentz violation with 8249 candidate electron antineutrino events taken by the Double Chooz experiment in 227.9 live days of running. This analysis, featuring a search for a sidereal time dependence of the events, is the first test of Lorentz invariance using a reactor-based antineutrino source. No sidereal variation is present in the data and the disappearance results are consistent with sidereal time independent oscillations. Under the Standard-Model Extension, we set the first limits on 14 Lorentz violating coefficients associated with transitions between electron and tau flavor, and set two competitive limits associated with transitions between electron and muon flavor.
    Physical Review D 12/2012; 86(11):112009. DOI:10.1103/PhysRevD.86.112009 · 4.86 Impact Factor
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    ABSTRACT: A database of toroidal momentum transport on five tokamaks, Alcator C-Mod, DIII-D, JET, NSTX and JT-60U, has been constructed under a wide range of conditions in order to understand the characteristics of toroidal momentum transport coefficients, namely the toroidal momentum diffusivity (chi(phi)) and the pinch velocity (V-pinch). Through an inter-machine comparison, the similarities and differences in the properties of chi(phi) and V-pinch among the machines have been clarified. Parametric dependences of these momentum transport coefficients have been investigated over a wide range of plasma parameters taking advantage of the different operation regimes in machines. The approach offers insights into the parametric dependences as follows. The toroidal momentum diffusivity (chi(phi)) generally increases with increasing heat diffusivity (chi(i)). The correlation is observed over a wide range of chi(phi), covering roughly two orders of magnitude, and within each of the machines over the whole radius. Through the inter-machine comparison, it is found that chi(phi) becomes larger in the outer region of the plasma. Also observed is a general trend for V-pinch in tokamaks; the inward pinch velocity (-V-pinch) increases with increasing chi(phi). The results that are commonly observed in machines will support a toroidal rotation prediction in future devices. On the other hand, differences among machines have been observed. The toroidal momentum diffusivity, chi(phi), is larger than or equal to chi(i) in JET and JT-60U; on the other hand, chi(phi) is smaller than or equal to chi(i) in NSTX, DIII-D and Alcator C-Mod. In DIII-D, the ratio -RVpinch/chi(phi) at r/a = 0.5-0.6 is about 2, which is small compared with that in other tokamaks (-RVpinch/chi(phi) approximate to 5). Based on these different observations, parametric dependences of chi(phi)/chi(i), RVpinch/chi(phi) and chi(phi) have been investigated in H-mode plasmas. Across the dataset from all machines, the ratio chi(phi)/chi(i) tends to be larger in low nu(e)* at fixed T-e/T-i and rho(pol)*. An increase in chi(phi) is observed with decreasing n(e) and/or increasing T-e. The pinch number (-RVpinch/chi(phi)) is observed to increase with increasing R/L-ne at both q(95) = 5.5-7.2 and q(95) = 3.7-4.5. Here nu(e)*, nu(pol)*, T-e, T-i, R/L-ne and q(95) are, respectively, the normalized effective electron collision frequency, the normalized ion poloidal Larmor radius, the electron and ion temperatures, the inverse ratio of density scale length, L-ne, to the major radius, R, and the safety factor at the 95% flux surface.
    Nuclear Fusion 12/2012; 52(12):123005. DOI:10.1088/0029-5515/52/12/123005 · 3.24 Impact Factor
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    ABSTRACT: We report on x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) studies of the paramagnetic (Mn,Co)-codoped ZnO [ZnO:(Mn,Co)] and ferromagnetic (Fe,Co)-codoped ZnO[ZnO:(Fe,Co)] nano-particles. Both the surface-sensitive total-electron-yield mode and the bulk-sensitive total-fluorescence-yield mode have been employed to extract the valence and spin states of the surface and inner core regions of the nano-particles. In the case of paramagnetic ZnO:(Mn,Co) nano-particles, the doped Mn and Co atoms are in a mixed-valence (2+, 3+, and 4+) state and the relative concentrations of the high-valence (3+ and 4+) Mn and Co ions are higher in the surface region than in the inner core region. In the case of the ferromagnetic ZnO:(Fe,Co) nano-particles, the doped Fe and Co atoms are found to be in a mixed-valence (2+ and 3+) state and the relative concentrations of the Fe 3+ and Co 3+ ions are higher in the surface region than in the inner core region. The XMCD spectra show that the Fe 3+ ions in the surface region mainly give rise to the ferromagnetism while the doped Co ions in the surface region show only paramagnetic behaviors. The transition-metal atoms in the inner core region do not show magnetic signals, meaning that they are nonmagnetic states due to antiferromagnetic coupling. The present result combined with the previous results on transition-metal-doped ZnO nano-particles suggest that doped holes, probably due to Zn vacancy formation at the surfaces of the nano-particles, rather than doped electrons are involved in the occurrence of ferromagnetism in these systems. [DOI: 10.1380/ejssnt.2012.594]
    e-Journal of Surface Science and Nanotechnology 11/2012; 3(10):594-598. DOI:10.1380/ejssnt.2012.594]
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    ABSTRACT: The first detailed measurements of ion-impurity dynamics for NBI-heated ELMy H-modes at the edge of the JT-60U tokamak are reported. We investigated the ability of external momentum/power input to modify and control the radial electric field, Er, and pedestal structures. The relationship between Er and pedestal structures of ion-impurity density, ni, and temperature, Ti, during the ELMing H-mode phase for various momentum input directions (i.e. co-, balanced- and counter-NBI) and input powers from perpendicular NBI are compared with the ELM-free phase. The observed trend is that the edge Er-well width increases in the co-NBI discharge, while the Er value at the base of the Er-well becomes more negative in the counter-NBI discharge. The scale length for both ni and Ti in the pedestal is ~2 cm and values are ~1 for both ELM-free and ELMing phases with different magnitudes of Er (and/or Er shear). Characteristics of the turbulent density fluctuation, in addition to a uniform toroidal MHD oscillation (i.e. n = 0), during both ELM-free and ELMing phases are also reported.
    Nuclear Fusion 10/2012; 52(11):114010. DOI:10.1088/0029-5515/52/11/114010 · 3.24 Impact Factor
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    ABSTRACT: Neutron energy spectra at 15 o and 90 o produced from aluminum, copper and tungsten targets bombarded with 120-GeV protons were measured at Fermilab Test Beam Facility. The target thicknesses were 50 cm for aluminum, 2 0 cm and 40 cm for copper, and 10 cm for tungsten, respectively. The neutron time-of-flight measurements were performed using an NE213 organic liquid scintillator (12.7 cm diameter, 12.7 cm long) at 5.2 m for 90 o and 8.0 m for 15 o measuring from the center of the target to the surface of the detector. The raw signals (waveforms) obtained from photomultiplier tubes were recorded using the 10 bit digitizer (Agilent-Acqiris DC282) with 0.5 ns sampling and 500 ns duration. To compare the experimental results, Monte Carlo calculations with the PHITS, FLUKA and MARS codes were performed. It was found that these calculated results at 90 o underestimate the experimental results due to the strong forward emission of particles in the models, while calculated results at 15 o gives good agreement with the data.
    10/2012; 3:65-68. DOI:10.15669/pnst.3.65

Publication Stats

3k Citations
605.22 Total Impact Points

Institutions

  • 2006–2014
    • Tohoku Gakuin University
      Japan
    • Yamagata University
      • Department of Physics
      Ямагата, Yamagata, Japan
  • 2002–2014
    • Japan Atomic Energy Agency
      • Nuclear Science and Engineering Directorate
      Muramatsu, Niigata, Japan
  • 2013
    • Kyoto University
      • Graduate School of Energy Science
      Kioto, Kyōto, Japan
  • 2008–2012
    • The Graduate University for Advanced Studies
      Миура, Kanagawa, Japan
  • 2008–2011
    • Tokai University
      • Department of Physics
      Hiratsuka, Kanagawa-ken, Japan
  • 2000–2011
    • The University of Tokyo
      • • Department of Physics
      • • Department of Astronomy
      • • Department of Quantum Engineering and Systems Sciences
      Tōkyō, Japan
  • 1989–2009
    • Kanazawa Medical University
      • Department of Ophthalmology
      Kanazawa, Ishikawa, Japan
    • The Physical Society of Japan
      Edo, Tōkyō, Japan
  • 2004–2007
    • National Institute of Radiological Sciences
      • Research Center for Charged Particle Therapy
      Tiba, Chiba, Japan
  • 2001–2007
    • High Energy Accelerator Research Organization
      • Accelerator Laboratory
      Tsukuba, Ibaraki, Japan
  • 2002–2005
    • Tohoku University
      • Department of Quantum Science and Energy Engineering
      Japan
  • 2001–2003
    • Rikkyo University
      Edo, Tōkyō, Japan
  • 2000–2003
    • Niigata University
      • Graduate School of Science and Technology
      Niahi-niigata, Niigata, Japan
  • 1994–2002
    • University of Tsukuba
      • Applied Physics
      Tsukuba, Ibaraki, Japan
  • 1998–2000
    • University of California, Los Angeles
      • Department of Surgery
      Los Ángeles, California, United States
  • 1997
    • Tokyo Junshin Women's College
      • Department of Hygiene and Public Health
      Edo, Tōkyō, Japan
  • 1995
    • Fukui National College Of Technology
      Hukui, Fukui, Japan
  • 1987–1989
    • Hokkaido University
      • • Laboratory of Nuclear Reactor Engineering
      • • School of Engineering
      Sapporo, Hokkaidō, Japan
    • RIKEN
      Вако, Saitama, Japan