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Kitazato, Kohei*; Milliken, R. E.*; Iwata, Takahiro*; Abe, Masanao*; Otake, Makiko*; Matsuura, Shuji*; Takagi, Yasuhiko*; Nakamura, Tomoki*; Hiroi, Takahiro*; Matsuoka, Moe*; et al.
Nature Astronomy (Internet), 5(3), p.246 - 250, 2021/03
Times Cited Count：43 Percentile：96.93(Astronomy & Astrophysics)Here we report observations of Ryugu's subsurface material by the Near-Infrared Spectrometer (NIRS3) on the Hayabusa2 spacecraft. Reflectance spectra of excavated material exhibit a hydroxyl (OH) absorption feature that is slightly stronger and peak-shifted compared with that observed for the surface, indicating that space weathering and/or radiative heating have caused subtle spectral changes in the uppermost surface. However, the strength and shape of the OH feature still suggests that the subsurface material experienced heating above 300 
C, similar to the surface. In contrast, thermophysical modeling indicates that radiative heating does not increase the temperature above 200 C at the estimated excavation depth of 1 m, even if the semimajor axis is reduced to 0.344 au. This supports the hypothesis that primary thermal alteration occurred due to radiogenic and/or impact heating on Ryugu's parent body.
Kitazato, Kohei*; Milliken, R. E.*; Iwata, Takahiro*; Abe, Masanao*; Otake, Makiko*; Matsuura, Shuji*; Arai, Takehiko*; Nakauchi, Yusuke*; Nakamura, Tomoki*; Matsuoka, Moe*; et al.
Science, 364(6437), p.272 - 275, 2019/04
Times Cited Count：259 Percentile：99.73(Multidisciplinary Sciences)The near-Earth asteroid 162173 Ryugu, the target of Hayabusa2 sample return mission, is believed to be a primitive carbonaceous object. The Near Infrared Spectrometer (NIRS3) on Hayabusa2 acquired reflectance spectra of Ryugu's surface to provide direct measurements of the surface composition and geological context for the returned samples. A weak, narrow absorption feature centered at 2.72 micron was detected across the entire observed surface, indicating that hydroxyl (OH)-bearing minerals are ubiquitous there. The intensity of the OH feature and low albedo are similar to thermally- and/or shock-metamorphosed carbonaceous chondrite meteorites. There are few variations in the OH-band position, consistent with Ryugu being a compositionally homogeneous rubble-pile object generated from impact fragments of an undifferentiated aqueously altered parent body.
Ida, Katsumi*; Sakamoto, Yoshiteru; Yoshinuma, Mikiro*; Takenaga, Hidenobu; Nagaoka, Kenichi*; Hayashi, Nobuhiko; Oyama, Naoyuki; Osakabe, Masaki*; Yokoyama, Masayuki*; Funaba, Hisamichi*; et al.
Nuclear Fusion, 49(9), p.095024_1 - 095024_9, 2009/09
Times Cited Count：29 Percentile：72.01(Physics, Fluids & Plasmas)Dynamics of ion internal transport barrier (ITB) formation and impurity transport both in the Large Helical Device (LHD) heliotron and JT-60U tokamak are described. Significant differences between heliotron and tokamak plasmas are observed. The location of the ITB moves outward during the ITB formation regardless of the sign of magnetic shear in JT-60U and the ITB becomes more localized in the plasma with negative magnetic shear. In LHD, the low Te/Ti ratio (
1) of the target plasma for the high power heating is found to be necessary condition to achieve the ITB plasma and the ITB location tends to expand outward or inward depending on the condition of the target plasmas. Associated with the formation of ITB, the carbon density tends to be peaked due to inward convection in JT-60U, while the carbon density becomes hollow due to outward convection in LHD. The outward convection observed in LHD contradicts the prediction by neoclassical theory.
Kobayashi, Takayuki; Terakado, Masayuki; Sato, Fumiaki; Yokokura, Kenji; Shimono, Mitsugu; Hasegawa, Koichi; Sawahata, Masayuki; Suzuki, Sadaaki; Hiranai, Shinichi; Igarashi, Koichi; et al.
Plasma and Fusion Research (Internet), 4, p.037_1 - 037_10, 2009/08
Electron cyclotron (EC) heating and current drive (CD) are key tools to control fusion plasma especially for effective electron heating and for suppression of neoclassical tearing mode (NTM). Recently, developments of a high power gyrotron and a power modulation technique have been successfully achieved on JT-60U ECRF system in order to enhance the system performance. Stable gyrotron oscillation with oscillation power of 1.5 MW for 1 s was demonstrated in 2007, for the first time. Then temperature rise of cavity and collector has been investigated. It has been shown that the longer pulse operation with 1.5 MW by an improved 110 GHz gyrotron is possible. In addition, modulated ECCD in synchronized with NTM rotation has been performed with the oscillation power of 0.8 MW and the frequency around 5 kHz. The synchronizing system has worked very well and it has played an essential role in NTM suppression experiments on JT-60U.
Noguchi, Kazuhiko*; Miyano, Hiroshi*; Muramatsu, Ken*; Narumiya, Yoshiyuki*; Takata, Takashi; Muta, Hitoshi*; Itoi, Tatsuya*; Matsumoto, Masaaki*; Matsunaga, Yoko*; Sugiyama, Kenichiro*
no journal, ,
The risk is used for an index to judge. The risk to be considered varies according to the purpose of the judgment. The analysis of the risk needs the knowledge of the nuclear energy system and society.
Miyano, Hiroshi*; Muramatsu, Ken*; Noguchi, Kazuhiko*; Narumiya, Yoshiyuki*; Takata, Takashi; Muta, Hitoshi*; Itoi, Tatsuya*; Matsumoto, Masaaki*; Matsunaga, Yoko*; Sugiyama, Kenichiro*
no journal, ,
In considering nuclear safety, it is an important task to clarify the relationship with "peace of mind" that is the heart of people. What is the state that scientific safety is something that people feel safe? We considered the relationship between quantified risk and safety, and ways to acquire peace of mind. We analyzed the thresholds of safety risks as a social common, showed a safe condition, and showed the importance of forming a consensus to obtain peace of mind.
Matsumoto, Masaaki*; Miyano, Hiroshi*; Noguchi, Kazuhiko*; Muramatsu, Ken*; Narumiya, Yoshiyuki*; Takata, Takashi; Muta, Hitoshi*; Itoi, Tatsuya*; Matsunaga, Yoko*; Sugiyama, Kenichiro*
no journal, ,
In society, understanding of risk is various. We will show how to understand risk and describe how to face risks in the society. Individual risks are accepted by individuals, but it is necessary for society to construct a structure in society that allows risks to be tolerated by society. For that purpose, we also describe what social risk is and how society and individuals face social risks and how to choose risks to accept. We consider not only the concept of nuclear risk but also how nuclear risk should be accepted from the viewpoint of disaster prevention for the public.
Matsunaga, Yoko*; Miyano, Hiroshi*; Noguchi, Kazuhiko*; Muramatsu, Ken*; Narumiya, Yoshiyuki*; Takata, Takashi; Muta, Hitoshi*; Itoi, Tatsuya*; Matsumoto, Masaaki*; Sugiyama, Kenichiro*
no journal, ,
After Fukushima Daiichi nuclear accident, it becomes more important risk communication with the public. In discussions with the public in nuclear safety, communication and discussions on risks that not only nuclear risks also social risks are important. Differences in viewpoints, understanding, and thought about risks become communication difficult. We need to discuss risks fairly, appropriately with the public and reduce total social risks.
Takata, Takashi; Miyano, Hiroshi*; Noguchi, Kazuhiko*; Muramatsu, Ken*; Narumiya, Yoshiyuki*; Muta, Hitoshi*; Itoi, Tatsuya*; Matsumoto, Masaaki*; Matsunaga, Yoko*
no journal, ,
A considering nuclear safety, it is an important task to clarify the relationship with "peace of mind" that is the heart of people. In this paper, a fundamental methodology of risk assessment for nuclear safety is introduced based on a probabilistic risk assessment (PRA) method. Furthermore, an application of the methodology for an external event is also discussed.
Narumiya, Yoshiyuki*; Miyano, Hiroshi*; Noguchi, Kazuhiko*; Muramatsu, Ken*; Takata, Takashi; Muta, Hitoshi*; Itoi, Tatsuya*; Matsumoto, Masaaki*; Matsunaga, Yoko*
no journal, ,
In order to grasp efficiency of risk information, we tried to apply an insight of PRA to considering of severe accidents; TMI, Chernobyl, and Fukushima Dai-ichi. Based on this analysis, three points are disclosed. At first, PRA can product adequate countermeasures for low-likelihood events; huge earthquake or Tsunami. Next, PRA can prove weak points in design or operation reasonably. Third point is safety culture. PRA and safety culture are seemed to be connected deeply. These analyses revealed PRA is one of the most efficient and systematic risk analysis methods to prevent/mitigate severe accidents.
Narumiya, Yoshiyuki*; Miyano, Hiroshi*; Noguchi, Kazuhiko*; Muramatsu, Ken*; Takata, Takashi; Muta, Hitoshi*; Itoi, Tatsuya*; Matsumoto, Masaaki*; Matsunaga, Yoko*
no journal, ,
Target of PRA is not calculating PRA to get CDF/CFF, but providing significant and useful information from PRA results for risk-informed activities. Lot of risk applications have been implemented these about 20 years in US. After Fukushima Dai-ichi accidents, Japanese Nuclear Regulation Authority provided new regulatory requirements about external events and beyond design events. And Risk Application faces full-scale implementation. In this report, several methods of risk application are showed with adequate risk indexes. Two examples of risk application, risk-informed shutdown management and RI-ISI, are provided. The explanation about Risk Informed Decision-Making Process is made.
Takir, D.*; Kitazato, Kohei*; Milliken, R. E.*; Iwata, Takahiro*; Abe, Masanao*; Otake, Makiko*; Matsuura, Shuji*; Arai, Takehiko*; Nakauchi, Yusuke*; Nakamura, Tomoki*; et al.
no journal, ,
JAXA spacecraft and sample return mission Hayabusa2 has arrived at the near-Earth asteroid 162173 Ryugu, which is classified a primitive carbonaceous object. Here we report recent results of near-infrared spectrometer (NIRS3) on the Hayabusa2 spacecraft. The observations provide direct measurements of the surface composition of Ryugu and context for the returned samples. NIRS3 has detected a weak and narrow absorption feature centered at 2.72 micrometer across entire observed surface. This absorption feature is attributed to the presence of OH-bearing minerals. The NIRS3 observations also revealed that Ryugu is the darkest object to be observed up-close by a visiting spacecraft. The intensity of the OH feature and low albedo are consistent with thermally-and/or shock-metamorphosed, and/or carbon-rich space-weathered primitive and hydrated carbonaceous chondrites.
Tekeda, Norito*; Tsuchida, Shoji*; Kuwafaki, Reiko*; Matsunaga, Yoko*; Horikoshi, Hidehiko*; Sata, Tsutomu
no journal, ,
We create a framework for evaluating risk communication based on evaluation indicators and evaluation methods that make use of the characteristics of risk communication such as collaboration and consensus building, and start a research project to consider methods for concrete social implementation. Therefore, I would like to give an overview of it.
