M. Osakabe

Kyoto University, Kioto, Kyōto, Japan

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Publications (434)551.43 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Measurement and control of divertor heat flux are a crucial issue for realization of fusion burning plasma. However, time-dependent heat flux is often difficult to be estimated experimentally, because thermal diffusion process in thermal probe tips takes time longer than the discharge duration of present experiments. A new reconstruction method for time dependent heat flux from the measurement of the thermal probe tip temperature is proposed in this paper. The heat flux of the Large Helical Device divertor leg was analyzed by the proposed method as the function of the time for the first time. This indicates that heat flux measurement with thermal probes would become a monitoring tools even for the future fusion devices. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
    Beiträge aus der Plasmaphysik 04/2014; 54(3).
  • Fuyuki Tachi, Masahiro Osakabe
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    ABSTRACT: Solar ultraviolet-B (UVB) radiation is deleterious to plant-dwelling mites. Neoseiulus californicus (McGregor) is a predominant predator of agriculturally important pest species of spider mite. However, phytoseiid mites are more vulnerable to UVB radiation than spider mites. Thus, the UVB radiation may influence decision making in foraging phytoseiid mites whether disperse or not. We tested the difference in impact and behavioral response among wavelengths of monochromatic UV radiation using a spectroscopic light source in N. californicus in the laboratory. We also examined whether the behavioral responses of N. californicus females to UV radiation varied based on the presence of prey (Tetranychus urticae Koch) eggs and residues (webs and excreta of T. urticae: foraging cue). The impact of UV radiation on the N. californicus egg hatchability varied drastically between wavelengths of ≤300 nm (0%) and ≥310 nm (100%). The N. californicus females escaped from UV radiation more quickly when they were irradiated with UV at shorter wavelength. Presence of T. urticae eggs had no effects arresting the escape of phytoseiid mites. In contrast, prey residues (including eggs) markedly detained N. californicus females from escaping under UV irradiation at ≥310 nm. However, N. californicus females quickly escaped when irradiated with UV at harmful 300 nm wavelength, regardless of prey cues. This indicates that the eyeless phytoseiid mite is capable of perceiving UV radiation, and whether escape or not is determined on the basis of harmful/harmless UV wavelength and presence/absence of foraging cues.
    Environmental Entomology 03/2014; · 1.31 Impact Factor
  • Yasumasa Murata, Masahiro Osakabe
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    ABSTRACT: Ambient ultraviolet-B (UVB) radiation causes lethal damage to spider mites, and the extent of photochemical effects is determined by cumulative irradiance in the two-spotted spider mite, Tetranychus urticae. However, the LD50 values obtained using a UVB lamp were much lower than those elicited by solar UVB radiation. As solar radiation includes intense visible light and UVA, we assumed that a photoreactivation mechanism would play a role to survive under solar radiation. We assessed the capacity for photoreactivation in T. urticae eggs and larvae, and found that the efficacy of photoreactivation was determined by the cumulative irradiance of visible light (VIS) after exposure to UVB radiation. The wavelength range effective for photoreactivation went from UVA to green. Next, we found that an increased time lag between UVB and VIS radiation reduced the photoreactivation efficacy in eggs. In contrast, a time lag ≤4 h did not affect that in larvae. We discussed the possibility that the timing of photoreactivation occurs related with phase-specific UVB vulnerability and outbreak symptoms due to UVB-induced DNA damage. Our results suggest that T. urticae depends on a photoreactivation mechanism, and that the photoreactivation efficiency probably caused the divergence in UVB impact between UV lamp and solar radiation.
    Experimental and Applied Acarology 02/2014; · 1.85 Impact Factor
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    ABSTRACT: A spectrally selective imaging system has been developed to obtain a distribution of Hα emissions at the extraction region in a hydrogen negative ion source. The diagnostic system consisted of an aspherical lens, optical filters, a fiber image conduit, and a charge coupled device detector was installed on the 1/3-scaled hydrogen negative ion source in the National Institute for Fusion Science. The center of sight line passes beside the plasma grid (PG) surface with the distance of 11 mm, and the viewing angle has coverage 35 mm from the PG surface. Two dimensional Hα distribution in the range up to 20 mm from the PG surface was clearly observed. The reduction area for Hα emission caused by beam extraction was widely distributed in the extraction region near the PG surface.
    The Review of scientific instruments 02/2014; 85(2):02A724. · 1.52 Impact Factor
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    ABSTRACT: The electron density was measured at various bias voltages to understand how the plasma grid bias affects the electron near the plasma grid in large-scaled negative ion sources. It was found that the response of the electron to the bias voltage changes depending on negative ion production processes. The electron density remarkably decreases with increasing the bias voltage in the pure-volume plasma. On the other hand, the electron density depends on the bias voltage weakly in the Cs-seeded plasma. In addition, it was observed that the response of the co-extracted electron current to the bias voltage has similar trend to that of the electron density.
    The Review of scientific instruments 02/2014; 85(2):02B131. · 1.52 Impact Factor
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    ABSTRACT: In the large helical device (LHD), the theoretically predicted width of the ordinary-extraordinary-electron Bernstein wave (O-X-B) mode conversion (MC) window is comparable to the beam width and the power deposition is located in the off-axis region if the 77GHz fundamental electron cyclotron (EC) wave of is launched from an existing horizontal port antenna. In the experiment, the actual MC window location was looked for with changing the aiming. The effective aiming with that the increase of the stored energy was observed was two degrees apart from the location of the theoretical MC window at a maximum. Measurement of the waves originated from the thermally emitted EBW and radiated via the B-X-O mode conversion process is effective to improve the accuracy of the theoretical prediction with comparison between the theoretical and the experimental results. The theoretical prediction suggests that the width of the MC window of the fundamental 77GHz EC wave can be expanded if the lower port antenna is used. On the other hand, the MC window of the second harmonic 154GHz EC wave is blocked by horizontal port wall if another horizontal port antenna is used. It is required to move the final mirror of the quasi-optical antenna toward the plasma surface. Focusing of the beam at the plasma cutoff is (PC) also necessary for the effective mode conversion.
    01/2014; 1580(1).
  • Source
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    ABSTRACT: Remarkable progress has been made in diagnosing energetic particle instabilities on present-day machines and in establishing a theoretical framework for describing them. This overview describes the much improved diagnostics of Alfven instabilities and modelling tools developed world-wide, and discusses progress in interpreting the observed phenomena. A multi-machine comparison is presented giving information on the performance of both diagnostics and modelling tools for different plasma conditions outlining expectations for ITER based on our present knowledge.
    10/2013;
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    ABSTRACT: Extraction structure of negative hydrogen ions (H‑) (i.e. the regions where H‑ ions are effectively extracted from the plasma) was obtained using hydrogen Balmer-α (Hα) imaging spectroscopy and cavity ring-down spectroscopy. The H‑ ion density increases after caesium (Cs) seeding through a surface conversion process on a Cs-covered plasma-grid (PG) surface. We found a reduction in the H‑ density during beam extraction after Cs conditioning, and the same signal reduction appeared in the Hα intensity caused by the reduction in the excited hydrogen (n = 3) population, which in turn is caused by the decrease in the mutual neutralization process between positive and negative hydrogen ions. We clearly observed the reduction structure of the Hα emissions in the extraction region; the structure expands at optimal Cs conditioning. From this result, the H‑ ions, which are produced at the PG surface, release to the extraction region and widely distribute during arc discharge. We conclude that the reduction of the H‑ density is caused by the particle loss due to beam extraction from the PG apertures.
    New Journal of Physics 10/2013; 15(10):3026-. · 4.06 Impact Factor
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    ABSTRACT: A reversal of intrinsic torque is observed during the formation of an internal transport barrier (ITB) in the Large Helical Device. The intrinsic torque evaluated from the disparity of rotation between coinjection and counterinjection changes sign from counter to codirection inside the ITB after the ITB formation. Both the internal transport barrier and the reversal of the intrinsic torque propagate inwards. This experiment demonstrates that the sign of the nondiffusive term of momentum transport is sensitive to the confinement mode of heat transport.
    Physical Review Letters 07/2013; 111(5). · 7.73 Impact Factor
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    ABSTRACT: Three-dimensional effects on plasma flows have been experimentally studied in the large helical device with 3D configurations. Spontaneous toroidal flow without net driving force using the combination of perpendicular neutral beam injection (NBI) heating and balanced tangential NBI heating has been investigated with two magnetic configurations. Co- and counter-directed spontaneous flows have been observed depending on the collisionality. Toroidal flow shear changes the sign at 0.4<reff<0.6 between co- and counter-flowing plasmas, where reff is a averaged minor radius. The detailed flow structures have been also examined at the edge region with stochastic magnetic field. A poloidal flow driven by the positive radial electric field has been observed at the open field region just outside of the plasma boundary. At the stochastic region, a shear of poloidal flow has been observed, while no shear of toroidal flow has been observed. The toroidal flow shear changes only in the nested magnetic flux surface region. A difference of density fluctuation property has been observed between co- and counter-flowing plasmas, where toroidal flow shears are formed.
    Physics of Plasmas 05/2013; 20(5). · 2.38 Impact Factor
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    ABSTRACT: A polymerase chain reaction (PCR)-restriction fragment length polymorphism (PCR-restriction fragment-length polymorphism)-based method for species identification was applied to 14 Tetranychus spider mite species, which were dominant species intercepted at Japanese import plant quarantine. We sequenced the internal transcribed spacer (ITS) region of the nuclear ribosomal DNA (rDNA), which included the partial ends of the 18S and 28S ribosomal RNA genes, 5.8S ribosomal RNA gene, and two internal transcribed spacers (ITS1 and ITS2) for 15 populations of the 14 species. We analyzed the recognition sites of four restriction endonucleases, which had been proposed for discrimination of Japanese Tetranychus species, and constructed a scheme for Tetranychus species identification by PCR-restriction fragment-length polymorphism. We then applied the scheme to 245 individuals from 199 populations, most of them were from foreign countries. As a result, all 14 species were correctly identified using PCR-restriction fragment-length polymorphism. This demonstrates the usefulness of the PCR-restriction fragment-length polymorphism method for the worldwide identification of Tetranychus species.
    Journal of Economic Entomology 04/2013; 106(2):661-8. · 1.60 Impact Factor
  • Masaaki Sudo, Masahiro Osakabe
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    ABSTRACT: The eggs of the herbivorous false spider mite Brevipalpus obovatus Donnadieu have a longer incubation period than those of spider mites and are not protected by webs. Brevipalpus obovatus often lays its eggs in the gaps among the hairs on host leaves. We examined the effects of stellate hairs of Viburnum erosum var. punctatum (VEP) leaves on the survival of B. obovatus eggs. Adult B. obovatus and Phytoseius nipponicus Ehara, a generalist predator, were introduced to VEP leaf disks; each B. obovatus egg was inspected daily until hatching. More eggs (63 vs. 42 %) survived on the abaxial surfaces of VEP leaves, where the stellate hairs are more complicated, than on the adaxial surfaces. Predation hazard decreased rapidly with increasing egg age and a substantial portion of the eggs hatched. Phytoseius nipponicus preyed on eggs regardless of egg age when mixed-age eggs were provided. Manipulative experiments with bent stellate hairs showed that the normal hairs reduced the predation risk of B. obovatus eggs by P. nipponicus. Therefore, the predation hazard was considered to decrease since the stellate hairs hindered the search for B. obovatus eggs by the phytoseiid mite.
    Experimental and Applied Acarology 02/2013; · 1.85 Impact Factor
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    ABSTRACT: The first results of saturation-currents polar distribution, which is measured with a directional Langmuir probe, at the beam extraction region of our caesium (Cs) seeded negative ion source have been reported. The line from maximum to minimum of the distribution tilts by 40° to the normal direction of the plasma grid (PG) surface. The maximum intensity is one order of magnitude larger than the minimum one. Depth distribution of the saturation currents is also measured along the axis of the PG aperture and the middle line between a pair of the axes of nearest neighbor PG apertures. Ionic plasma with quite low electron density is generated within a distance of 10 mm from PG. With a bias voltage lower than plasma potential, the difference between negative to positive saturation currents, which corresponds to electron current, increases rapidly beyond the boundary of ionic plasma. The electron current decreases by a factor of 6 with increasing the bias voltage from 2.8 to 6.4 V.
    02/2013;
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    ABSTRACT: Characteristics of negative-hydrogen ion (H-) density in the vicinity of plasma grid (PG) which is a boundary electrode between plasma and beam were experimentally investigated in cesium-seeded H- source. The H- density was measured with Cavity Ring Down method (CRD). Our CRD system has been upgraded from fixed line measurement to movable one which provides a profile measurement of the H- density. The H- density above the PG aperture is lower than that above the PG metal surface, and this density structure become to disappear in further region from the PG surface. The H- density decreases with positive bias voltage where an arc discharge chamber is higher potential than the PG. On the other hand, the H- density does not largely change with negative bias voltage. Reduction of the H- density was observed when a beam extraction voltage is applied. The reduction occurs in the case of lower bias voltage close to plasma potential. The extraction voltage influences H- density to a greater degree than bias voltage in low bias voltage region.
    02/2013;
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    ABSTRACT: Intense hydrogen-negative-ion source development, conducted at National Institute for Fusion Science (NIFS), is reviewed. Presently, the developed negative-ion sources are utilized in the negative-ion-based neutral beam injectors, which are installed to the Large Helical Device, the world's largest superconducting fusion machine, and the total injection power has achieved 16MW with the energy of 180-190 keV using three injectors with six sources. In the developed negative-ion accelerator with multi-slotted grounded grid, the grid heat load is much reduced due to its high transparency, leading to a high-energy acceleration of a high-current negative ion beam. As a result, one ion source produces 190keV-37A of negative ions for 1.6sec at maximum, corresponding to 340A/m2 of the current density. For further improvement of the negative ion source, plasma characteristics are investigated in the extraction region with a multi-diagnostics system. With the Cs seeding, the H- density increases and the electron density decreases, and, finally, an ion-ion plasma which consists of almost positive and negative ions is observed. The measured negative ion density is not largely decreased toward the plasma grid surface, on which the negative ion is produced. Reduction of the negative ion density is observed by the negative ion extraction, and invasion of the electric field for the negative ion extraction is recognized. Understanding of the negative ion transport in the plasma and the mechanism of the negative ion extraction should contribute to improvement of the source performance.
    02/2013;
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    ABSTRACT: Plant‐dwelling mites are potentially exposed to solar ultraviolet‐B (UVB) radiation that causes deleterious and often lethal effects, leading most mites to inhabit the lower (underside) leaf surfaces. However, in species of spider mite belonging to the Genus Panonychus, a substantial portion of individuals occur on upper leaf surfaces. We investigated whether the upper leaf surfaces of citrus trees are favorable for P. citri, and to what extent they are tolerant to UVB radiation. If eggs are not adequately protected from UVB damage, females may avoid ovipositing on the upper surfaces of sunny leaves. To test this, we conducted laboratory experiments using a UVB lamp, and semioutdoor manipulative experiments. As a result, P. citri eggs are tolerant to UVB. Field studies revealed that the ratio of eggs and adult females on upper leaf surfaces were larger for shaded than for sunny leaves. However, 64–89% of eggs hatched successfully even on sunny upper leaf surfaces. Nutritional evaluation revealed that whether on sunny or shaded leaves, in fecundity and juvenile development P. citri reaped the fitness benefits of upper leaf surfaces. Consequently, P. citri is tolerant to UVB damage, and inhabiting the upper surfaces of shaded leaves is advantageous to this mite.
    Photochemistry and Photobiology 01/2013; 89(2). · 2.29 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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    ABSTRACT: Dynamic transport study taking account of the slowing-down effect on the neutral beam injection heating is applied to a high ion temperature plasma with an ion internal transport barrier (ITB) obtained by carbon pellet injection, which records the highest ion temperature of around ~7 keV in the Large Helical Device. The transient increase in ion heating is clarified during the density decay phase just after the carbon pellet injection by considering the slowing-down effect. The dynamic transport analysis also includes the change in heat flux due to the change in kinetic energy inside the plasma with the time scale of the global energy confinement time, which is required to investigate the heat and momentum transport during the transient phase more exactly. The characteristics of the ion heat and momentum transport improvement during the ion ITB formation phase are clarified by the dynamic transport study.
    Plasma Physics and Controlled Fusion 12/2012; 55(1):014011. · 2.37 Impact Factor
  • Yasumasa Murata, Masahiro Osakabe
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    ABSTRACT: To determine whether the Bunsen-Roscoe reciprocity law (i.e., the extent of photochemical effects is determined by cumulative irradiance) is applicable to ultraviolet-B (UVB) damage in the twospotted spider mite Tetranychus urticae, egg hatchability and survival of individuals were assessed after irradiation with a UVB lamp using various combinations of intensity and time length. A positive linear correlation between probit mortality and cumulative UVB irradiance was detected in eggs, larvae, teleiochrysalis females, and adult females, regardless of UVB intensity (0.19-0.58 W m(-2)). LD(50) values were clearly higher in adult females, followed by teleiochrysalis females, larvae, and eggs. In eggs, reciprocity was obeyed not only at the UVB intensities listed above, but also at very low UVB intensity (0.014-0.023 W m(-2)). Such reciprocity in the negative effects of UVB radiation was also observed for the developmental rate of juveniles and egg production of adult females. However, the LD(50) value of eggs obtained using the UVB lamp (0.58 kJ m(-2)) was lower than that elicited by solar UVB radiation in a previous outdoor experiment (about 50 kJ m(-2)). These results suggest that a photoreactivation mechanism plays an important role in the survival of this mite under solar radiation.
    Journal of insect physiology 12/2012; · 2.24 Impact Factor
  • Fuyuki Tachi, Masahiro Osakabe
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    ABSTRACT: Ambient ultraviolet-B (UVB) radiation impacts plant-dwelling arthropods including herbivorous and predatory mites. However, the effects of UVB on prey-predator systems, such as that between the herbivorous spider mite and predatory phytoseiid mite, are poorly understood. A comparative study was conducted to determine the vulnerability and behavioral responses of these mites to ultraviolet (UV) radiation. First, we analyzed dose-response (cumulative irradiance-mortality) curves for the eggs of phytoseiid mites (Neoseiulus californicus, Neoseiulus womersleyi, and Phytoseiulus persimilis) and the spider mite (Tetranychus urticae) to UVB radiation from a UV lamp. This indicated that the phytoseiid mites were more vulnerable than the spider mite, although P. persimilis was slightly more tolerant than the other two phytoseiid mites. Second, we compared the avoidance behavior of adult female N. californicus and two spider mite species (T. urticae, a lower leaf surface user; Panonychus citri, an upper leaf surface user) in response to solar UV and visible light. N. californicus actively avoided both types of radiation, whereas P. citri showed only minimal avoidance behavior. T. urticae actively avoided UV as well as N. californicus but exhibited a slow response to visible light as well as P. citri. Such variation in vulnerability and avoidance behavior accounts for differences in the species adaptations to solar UVB radiation. This may be the primary factor determining habitat use among these mites on host plant leaves, subsequently affecting accessibility by predators and also intraguild competition.
    Naturwissenschaften 10/2012; · 2.14 Impact Factor

Publication Stats

1k Citations
551.43 Total Impact Points

Institutions

  • 2003–2014
    • Kyoto University
      • Graduate School of Agriculture / Faculty of Agriculture
      Kioto, Kyōto, Japan
  • 1995–2014
    • National Institute for Fusion Science
      Tokitsu-chō, Gifu, Japan
  • 2002–2003
    • The University of Tokyo
      • • Department of Agricultural and Environmental Biology
      • • Department of Biological and Environmental Engineering
      Tokyo, Tokyo-to, Japan
  • 2000
    • Australian National University
      • Plasma Research Laboratory (PRL)
      Canberra, Australian Capital Territory, Australia
    • National Agriculture and Food Research Organization
      Tsukuba, Ibaraki, Japan
  • 1994–1999
    • The Graduate University for Advanced Studies
      • Department of Fusion Science
      Миура, Kanagawa, Japan
  • 1998
    • Princeton University
      • Princeton Plasma Physics Laboratory
      Princeton, NJ, United States
  • 1996
    • National Engineering Research Center for Vegetables
      Peping, Beijing, China