N. Yanagi

National Institutes Of Natural Sciences, Edo, Tōkyō, Japan

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Publications (242)230.49 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Based on the successful plasma experiments in the Large Helical Device (LHD), design activities of the LHD-type helical fusion reactor FFHR-d1 are progressing at National Institute for Fusion Science (NIFS). A 100 kA current capacity is required for the winding conductor under the maximum magnetic field of similar to 12 T. The high-temperature superconductor (HTS) is a promising option for the helical coil conductor. For the development of such a HTS conductor suitable for the helical fusion reactor, we fabricated 30 kA-class HTS conductor samples, and the excitation tests were successfully carried out. We then fabricated and tested a 100-kA class HTS conductor. The conductor sample is a one-turn short-circuit coil with a race-track shape having a bridge-type mechanical lap joint. The transport current of the sample was induced by changing the external magnetic field, then the critical current of the sample was measured. A numerical analysis of the critical current is being performed by self-consistently solving the spatial distributions of the current density and magnetic field among the simply-stacked HTS tapes to verify the measured critical current of the samples. The critical current characteristics of a single HTS tape is evaluated by the percolation model in the precise analysis.
    IEEE Transactions on Applied Superconductivity 06/2015; 25(3):1-5. DOI:10.1109/TASC.2014.2377793 · 1.32 Impact Factor
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    ABSTRACT: An innovative winding method is developed by connecting high-temperature superconducting (HTS) conductors to enable efficient construction of a magnet system for the helical fusion reactor FFHR-d1. A large-current capacity HTS conductor, referred to as STARS, is being developed by the incorporation of several innovative ideas, such as the simple stacking of state-of-the-art yttrium barium copper oxide tapes embedded in a copper jacket, surrounded by electrical insulation inside a conductor, and an outer stainless-steel jacket cooled by helium gas. A prototype conductor sample was fabricated and reached a current of 100 kA at a bias magnetic field of 5.3 T with the temperature at 20 K. At 4.2 K, the maximum current reached was 120 kA, and a current of 100 kA was successfully sustained for 1 h. A low-resistance bridge-type mechanical lap joint was developed and a joint resistance of 2 nΩ was experimentally confirmed for the conductor sample.
    Nuclear Fusion 05/2015; 55(5):053021. DOI:10.1088/0029-5515/55/5/053021 · 3.24 Impact Factor
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    ABSTRACT: NIFS launched the Fusion Engineering Research Project (FERP) in preparation for DEMO by starting the redesign of the LHD-type helical reactor FFHR-d1. In the first round, the main parameters were selected. The second round is preparing detailed three-dimensional (3D) design of the superconducting magnet support structures, and 3D neutronics analyses, where the diverter targets can be efficiently shielded from fast neutrons. A new Flinabe blanket mixed with metal powder was proposed. Fabrication of helical coils by connecting half-helical-pitch segments of 100 kA-class YBCO high-temperature superconductors is proposed as a promising method. Also in progress is improvement of the first round of the core plasma design, ignition start-up analyses, and fueling scenario. As a consequence, a multi-path strategy on FFHR-d1 has been introduced with versions of -d1A, -d1B, and -d1C, where design flexibility is expanded to include subignition with options FFHR-c1 for “before demo, compact, and component-test.”
    Fusion Engineering and Design 10/2014; 89(9-10). DOI:10.1016/j.fusengdes.2014.02.076 · 1.15 Impact Factor
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    ABSTRACT: FFHR-d1 is a conceptual design of the helical reactor being developed at the National Institute for Fusion Science. The maintenance of in-vessel components is very important for the fusion demo reactor. In addition, sufficient pathways are needed for the divertor exhaust. To implement these, the vacuum vessel, coil support structure, and cryostat require large apertures. However, the coil support structure has to be sufficiently rigid to remain within soundness and deformation limits. A design combining the structural components in the FFHR-d1A was developed from mechanical and thermal viewpoints. Consequently, components having a sufficiently large port area were provided. An investigation of the maintenance and exhaust schemes has been planned on the basis of this fundamental design.
    Fusion Engineering and Design 10/2014; 89(9-10). DOI:10.1016/j.fusengdes.2014.02.058 · 1.15 Impact Factor
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    ABSTRACT: This study examines the relationship between toner exposure and its health effects in terms of biomarkers which are known to assess the damages to humans caused by toxic material exposure.
    Human &amp Experimental Toxicology 07/2014; 34(4). DOI:10.1177/0960327113512339 · 1.41 Impact Factor
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    ABSTRACT: This study uses pulmonary function tests and chest x-ray examinations to examine the relationship between toner-handling work and its health effects.
    Human &amp Experimental Toxicology 07/2014; 34(4). DOI:10.1177/0960327113520018 · 1.41 Impact Factor
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    ABSTRACT: Objectives Focusing on the respiratory function for health effect indices, we conducted a cross-sectional study on workers with and without toner handling to compare the longitudinal changes. Methods Among 116 subjects who worked for a Japanese business-equipment manufacturer and participated in the study, the analysis included 69 male workers who we were able to follow up for 4 years. We categorized the 40 workers engaged in toner-handling work as the exposed group and the 29 workers not engaged in these tasks as the referent group, and compared their respiratory function test results: PEFR, VC, %VC, FEV1.0 and FEV1.0%. Results The cross-sectional study of the respiratory function test results at the baseline and at the 5th year showed no statistically significant differences in PEFR, VC, %VC, FEV1.0 and FEV1.0% between the exposed and referent workers. Also, respiratory function time-course for 4 years was calculated and compared between the groups. No statistically significant differences were shown. Conclusion Our study does not suggest any toner exposure effects on respiratory function. However, the number of subjects was small in our study; studies of larger populations will be desired in the future.
    Safety and Health at Work 07/2014; 5(4). DOI:10.1016/j.shaw.2014.07.001
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    ABSTRACT: Design activities on the helical-type fusion DEMO reactor, FFHR-d1, are progressing at NIFS. A 100 kA current-capacity is required for the helical coil conductors under the maximum magnetic field of ~ 13 T. High-temperature superconducting conductor has been proposed as one of the conductor options for the FFHR-d1 magnet. In this study, a 30 kA class HTS conductor sample has been fabricated and tested. The sample had no current feeders and the current was induced by changing the background magnetic field generated by the 9 T split coils in the cryostat. Rogowski coils and Hall probes were used for the measurement of the transport current of the sample. The critical current of the sample was measured at various temperatures and bias magnetic fields. To verify the self-field effect of the sample, a numerical analysis was performed by considering the current and magnetic field distribution among the tapes self-consistently. The analysis result was compared with the experimental observation.
    IEEE Transactions on Applied Superconductivity 06/2014; 24(3):1-5. DOI:10.1109/TASC.2013.2287715 · 1.32 Impact Factor
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    ABSTRACT: The high-temperature superconducting magnet option is being explored in the conceptual design studies of the LHD-type helical fusion reactor FFHR-d1. A 100 kA-class conductor is being developed by simply stacking REBCO tapes in a copper and stainless-steel jacket. One of the design options of the HTS conductor includes internal insulation so that the windings do not require vacuum pressure impregnation process. Innovative winding method of the huge helical coils is being investigated based on the segment fabrication of half-helical-pitch conductors by developing a bridge-type mechanical lap joint. A “30 kA-class” prototype conductor sample was fabricated using GdBCO tapes and successfully tested. The critical current was measured at various temperatures at 4.2-40 K and magnetic field <; 8 T. The joint resistance was evaluated by changing the applied stress. These experimental results are boosting the HTS magnet design of FFHR-d1.
    IEEE Transactions on Applied Superconductivity 06/2014; 24(3):1-5. DOI:10.1109/TASC.2013.2292775 · 1.32 Impact Factor
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    ABSTRACT: The upgrading plan of the Mini-RT which is an experimental device for plasma physics was initiated to replace the magnetically-levitated high temperature superconducting (HTS) coil by the new one wound with the latest REBCO tapes. The performance of the new HTS coil has been examined at the National Institute for Fusion Science. The coil was indirectly cooled to 35 K by forced flow of cold helium gas. The coil was successfully excited up to 100 A with a proper persistent current switch (PCS) operation. The central field given by the Hall probe was 0.21 T, which was the same with that expected by a numerical calculation. The time constant of the current decay during the persistent current mode was evaluated at the coil temperature of 36 and 41 K to be 306 and 228 h, respectively. These values are consistent with the estimation based on the measured joint resistances and they are much longer than that of the previous floating coil of Mini-RT wound 10 years ago (41 h before aged deterioration). By the test results, it has been confirmed that the promising performance of the manufactured REBCO floating coil has been achieved to further promote the Mini-RT project.
    IEEE Transactions on Applied Superconductivity 06/2014; 24(3):1-4. DOI:10.1109/TASC.2013.2287706 · 1.32 Impact Factor
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    ABSTRACT: This study examines the relationship between toner-handling work and its health effects on self-reported respiratory symptoms. The subjects were 1,504 male workers in a Japanese toner and photocopier manufacturing company. Personal exposure measurement, pulmonary function tests, chest X-ray examination, measurement of biomarkers, and a questionnaire about self-reported respiratory symptoms were performed annually. This study discusses the questionnaire results. We found that the toner-handling group showed significantly higher prevalence of breathlessness than the never-toner-handling group. The significant reduction of pulmonary function and fibrosis change in the chest X-ray examination associated with breathlessness were not observed. However the morbidity of asthma was higher compared to the Japanese population in both of the toner-handling group and the never-toner handling group, the effect of toner exposure was not clarified. Nevertheless, while the toner exposure levels in the current well-controlled working environment may be sufficiently low to prevent adverse health effects, further studies are needed to assess the more long-term latent health effects of toner exposure.
    02/2014; 2014:826757. DOI:10.1155/2014/826757
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    K. Natsume · T. Mito · N. Yanagi · H. Tamura
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    ABSTRACT: A new method of including cryogenic oscillating heat pipes (OHPs) in the HTS coil windings as a thermal transport device has been studied. In this work, two type of OHPs are tested in low temperature. Employed working fluids are H2, Ne, N2. We have attained high performance thermal property using a bent-pipe cryogenic OHP as a prototype. Obtained effective conductivities have reached to 46000 W/m K. Then a flat-plate cryogenic OHP has been developed, that is suitable for imbedding in magnet windings. Preliminary experiments have been conducted and the result has been promising.
    Physics Procedia 12/2013; 45:233–236. DOI:10.1016/j.phpro.2013.05.010
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    O. Mitarai · A. Sagara · R. Sakamoto · N. Yanagi · T. Goto
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    ABSTRACT: We present the newly discovered control algorithm for the heating power during ignition access to the thermally unstable ignition regime in the FFHR helical reactor. We used the fact that the thermally unstable and stable ignition regimes on Plasma Operating Contour map (POPCON) have an inverse relationship with respect to the density and temperature. As the density limit restricts the operating point to the thermally stable regime, the postulated temperature limit restricts the operating point to the thermally unstable regime. As a result, the heating power for feedback control is expressed by the measured temperature and power balance terms such as alpha heating and bremsstrahlung loss powers. The external heating power thus obtained is applied during the low-density NBI penetration phase, and then switched off automatically after over-passing the saddle point by alpha-heating power, reaching high-density ignition regime. This control algorithm is robust to various perturbations of the confinement factor, impurity content and so on. Feedback control algorithms thus established for both fueling and heating makes the thermally unstable operation more realistic in FFHR.
    Fusion Engineering and Design 10/2013; 88(6-8):1046-1049. DOI:10.1016/j.fusengdes.2013.03.033 · 1.15 Impact Factor
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    ABSTRACT: A conceptual design for the helical DEMO reactor FFHR-d1 is under development at the National Institute for Fusion Science. In the large helical device (LHD)-type configuration of FFHR-d1, the space between the plasma boundary and the helical coil is limited. Many components are required to be installed at definite geometric positions within this space. The position of each component changes owing to variations in the surrounding conditions, such as temperature, electromagnetic forces, and support methods. This paper proposes a radial-build design concept; the application of this concept ensures constant geometric positions of the components and the gaps between them during normal operation and the construction/maintenance phase. On the other hand, large apertures are required for the coil support structure for the maintenance of blanket and divertor systems. This paper presents a structural design procedure for the coil support structure with large apertures and an LHD-type gravity support post. The analytic results show that the stress level of the structure is lower than the permissible limit.
    Fusion Engineering and Design 10/2013; 88(9-10):2033-2037. DOI:10.1016/j.fusengdes.2013.02.027 · 1.15 Impact Factor
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    ABSTRACT: The progress of physical understanding as well as parameter improvement of net-current-free helical plasma is reported for the Large Helical Device since the last Fusion Energy Conference in Daejeon in 2010. The second low-energy neutral beam line was installed, and the central ion temperature has exceeded 7 keV, which was obtained by carbon pellet injection. Transport analysis of the high-Ti plasmas shows that the ion-thermal conductivity and viscosity decreased after the pellet injection although the improvement does not last long. The effort has been focused on the optimization of plasma edge conditions to extend the operation regime towards higher ion temperature and more stable high density and high beta. For this purpose a portion of the open helical divertors are being modified to the baffle-structured closed ones aimed at active control of the edge plasma. It is compared with the open case that the neutral pressure in the closed helical divertor increased by ten times as predicted by modelling. Studies of physics in a three-dimensional geometry are highlighted in the topics related to the response to a resonant magnetic perturbation at the plasma periphery such as edge-localized-mode mitigation and divertor detachment. Novel approaches of non-local and non-diffusive transport have also been advanced.
    Nuclear Fusion 10/2013; 53(10):104015. DOI:10.1088/0029-5515/53/10/104015 · 3.24 Impact Factor
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    ABSTRACT: The Large Helical Device is the world's largest heliotron/stellarator as well as the largest superconducting fusion device. Its construction started in 1990, and the plasma experiments started in March 1998 as planned, owing to strongly supported by concentrated R&D activities for superconducting magnets, heating devices and diagnostics. In 15 years since the initial operation, considerable efforts have been devoted to technology R&D activities in the areas of cryogenic engineering, plasma-facing components, heating devices, and diagnostics. These efforts have contributed to the advancement of plasma parameters toward the target values. The obtained results as well as the experiences should contribute to ITER and the next fusion reactors.
    Fusion Engineering (SOFE), 2013 IEEE 25th Symposium on; 01/2013
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    H. Tamura · N. Yanagi · T. Goto · K. Takahata · S. Imagawa · A. Sagara
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    ABSTRACT: The helical coil (HC) of a large helical device- (LHD-) type reactor has a non-axisymmetric three-dimensional (3-D) geometry and is wound continuously through the toroidal circumference. A simple calculation method can be useful in the early design phase for estimating the effect of many geometrical and structural parameters on the coil's behavior. An axisymmetric coil model having the mean radius of curvature of the HC has been proposed for estimating the stress distribution inside the coil. To ensure precision, several non-axisymmetric 3-D models were prepared, and the differences among them were investigated. The resulting axisymmetric model can estimate the stress distribution by difference of approximately 20% between the typical 3-D models. However, the deformation can be estimated accurately only by using the 3-D models. (C) 2011 Published by Elsevier B.V. Selection and/or peer-review under responsibility of the Guest Editors.
    Physics Procedia 12/2012; 36:1077-1082. DOI:10.1016/j.phpro.2012.06.109
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    ABSTRACT: Abstract Background: Interleukins, interferons and oxidative DNA products are important biomarkers assessing the inflammations and tissue damages caused by toxic materials in the body. We tried to evaluate distributions, reference values and age related changes of blood levels of inflammatory cytokines, C-reactive protein (CRP), IgE and urine levels of 8-hydroxy-2'-deoxyguanosine (8-OHdG) among workers in a cohort study evaluating the health influences of toner particles. Methods: A total of 1366 male workers under age 50 years (age 19-49 years; 718 exposed and 648 not exposed to toner particles) in a cross sectional study of 1614 (categorized as 809 exposed and 805 not exposed, age 19-59 years) workers in a photocopier company has been followed prospectively as the cohort. Blood levels of interleukin (IL)-4, IL-6, IL-8, interferon-γ (IFN-γ), CRP, IgE and urine 8-OHdG were measured annually for 5 years. Results: Reference values of the biomarkers are; CRP: 0.01-0.63×10-2g/L, IgE: 6-1480 IU/mL, IL-4: 2.6-76.1 pg/mL, IL-6: 0.4-4.9 pg/mL and 8-OHdG: 1.5-8.2 ng/mgCr. We could not evaluate reference values for IL-8 and IFN-γ because most of the values were below the sensitivity limits (2.0 pg/mL and 0.1 IU/mL, respectively). There were no differences of the biomarker levels between the toner exposed and the control workers. We observed a statistically significant age related decrease of serum IL-4 levels. Conclusions: This is the first report assessing the distributions and reference values of inflammatory biomarker levels in a large scaled cohort. We observed age related changes of some of the biomarkers. We could not detect any differences of the studied biomarker values between the toner exposed and the control workers.
    Clinical Chemistry and Laboratory Medicine 08/2012; 51(2). DOI:10.1515/cclm-2012-0330 · 2.96 Impact Factor
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    ABSTRACT: A new design activity is under way for a helical type DEMO reactor FFHR-d1. The first stage of the activity involves the fundamental issues related to three-dimensional blanket design: (1) the minimum blanket space required for reactor parameter decisions, (2) the support method for the helical blanket system, and (3) the blanket module design. Investigations have been performed with neutronics and mechanical finite-element method calculations. Neutronics investigations indicate that a tungsten carbide radiation shield could reduce the minimum blanket space requirement by ∼30 cm at the inboard region of FFHR-d1 compared with the blanket space of ∼100 cm in the previous FFHR2 design. The investigations also showed that main shielding materials, ferritic steel and B4C, could be used separately in a two-layered shielding configuration. The ferritic steel layer of the radiation shield is considered suitable to support the helical blanket system instead of relying on a thin vacuum vessel of the helical reactor. A size of a blanket module for a replacement process and the preferable cooling channel direction under a magnetic field are also discussed.
    Fusion Engineering and Design 08/2012; 87(s 5–6):584–588. DOI:10.1016/j.fusengdes.2012.01.049 · 1.15 Impact Factor

Publication Stats

1k Citations
230.49 Total Impact Points


  • 2009–2015
    • National Institutes Of Natural Sciences
      Edo, Tōkyō, Japan
  • 2012–2014
    • University of Occupational and Environmental Health
      • Institute of Industrial Ecological Sciences
      Kitakyūshū, Fukuoka, Japan
  • 1999–2014
    • The Graduate University for Advanced Studies
      Миура, Kanagawa, Japan
  • 1991–2014
    • National Institute for Fusion Science
      • Department of Helical Plasma Research
      Tokitsu-chō, Gifu, Japan
  • 2002–2011
    • Kyoto University
      • Graduate School of Energy Science
      Kyoto, Kyoto-fu, Japan
  • 2005
    • Seikei University
      Edo, Tōkyō, Japan
  • 2004
    • Waseda University
      Edo, Tōkyō, Japan
  • 2000–2003
    • Kyushu University
      Hukuoka, Fukuoka, Japan
  • 2001–2002
    • Tokai University
      Hiratuka, Kanagawa, Japan
  • 1992–1994
    • Kagoshima University
      • Faculty of Engineering
      Kagosima, Kagoshima, Japan