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Journal Articles

Information on ITER project, 50

Moriyama, Setsuko; Kajita, Shin*; Neyatani, Yuzuru

Purazuma, Kaku Yugo Gakkai-Shi, 91(3), p.231 - 232, 2015/03

no abstracts in English

Journal Articles

Fatal damages due to breakdown on a diagnostic mirror located outside the vaccum vessel in JT-60U

Kajita, Shin*; Hatae, Takaki; Sakuma, Takeshi; Takamura, Shuichi*; Ono, Noriyasu*; Itami, Kiyoshi

Plasma and Fusion Research (Internet), 7(Sp.1), p.2405121_1 - 2405121_4, 2012/09

Journal Articles

Development of prototype YAG laser amplifier for the edge Thomson scattering system in ITER

Hatae, Takaki; Hayashi, Toshimitsu; Yatsuka, Eiichi; Kajita, Shin*; Yoshida, Hidetsugu*; Fujita, Hisanori*; Nakatsuka, Masahiro*; Yahagi, Kenichi*; Shinobu, Katsuya*; Ono, Takehiro; et al.

Journal of Plasma and Fusion Research SERIES, Vol.9, p.253 - 258, 2010/08

Journal Articles

Design study of the divertor Thomson scattering system for JT-60SA

Kajita, Shin*; Hatae, Takaki; Itami, Kiyoshi; Ono, Noriyasu*; Nakano, Tomohide

Journal of Plasma and Fusion Research SERIES, Vol.9, p.157 - 162, 2010/08

Journal Articles

Progress in development of the advanced Thomson scattering diagnostics

Hatae, Takaki; Howard, J.*; Ebizuka, Noboru*; Yoshida, Hidetsugu*; Nakatsuka, Masahiro*; Fujita, Hisanori*; Narihara, Kazumichi*; Yamada, Ichihiro*; Funaba, Hisamichi*; Hirano, Yoichi*; et al.

Journal of Physics; Conference Series, 227, p.012002_1 - 012002_6, 2010/06

 Times Cited Count:2 Percentile:69.52

Journal Articles

Optimization of optical filters for ITER edge Thomson scattering diagnostics

Kajita, Shin; Hatae, Takaki; Naito, Osamu

Fusion Engineering and Design, 84(12), p.2214 - 2220, 2009/12

 Times Cited Count:9 Percentile:56.98(Nuclear Science & Technology)

In ITER edge Thomson scattering measurement system, it is planned that polychromators by use of optical band-pass filters and avalanche photodiodes are used for the detection system. In this paper, the optimization of the filter transmission wavelength ranges is performed by minimizing the numerically calculated electron temperature error. The Thomson spectrum extends to considerably short wavelength range because high electron temperature measurement is required; therefore, it is important to eliminate the line emission from the plasma, such as $$D_{alpha}$$, in particular. It is shown that a filter, the transmission wavelength of which is shorter than $$D_{alpha}$$, becomes important to decrease the error in high temperature regime. Moreover, when the filter number is more than 7, it is found that a filter, the transmission wavelength of which is higher than the laser wavelength of 1064 nm, is useful to reduce the averaged error in wide temperature range.

Journal Articles

Experimental studies on in-vessel tritium inventory in complicated environment of fusion reactors

Ueda, Yoshio*; Hino, Tomoaki*; Ono, Noriyasu*; Takagi, Ikuji*; Nakano, Tomohide; Tanabe, Tetsuo*; Kajita, Shin*; Fukumoto, Masakatsu

Purazuma, Kaku Yugo Gakkai-Shi, 85(10), p.684 - 694, 2009/10

Relation between deuterium retention, wall temperature and hydrocarbon generation in 30-s H-mode discharges of JT-60U was described. In discharges with a density below 50% of the Greenwald density, the trend of the deuterium retention against pulse number depended on the wall temperature: with increasing pulse number, the deuterium retention decreased at a wall temperature of 300 $$^{circ}$$C, decreased gradually at 150 $$^{circ}$$C, and remained constant at 80 $$^{circ}$$C. In contrast, in discharges with high densities above 70% of the Greenwald density, the deuterium retention increased with increasing pulse number at the above three wall temperatures. In the high density discharges, the deuterium retention flux increased with increasing hydrocarbon generation flux, suggesting that the deuterium is retained in co-deposition layers of carbon, which originated from the hydrocarbons.

Journal Articles

Engineering and maintenance studies of the ITER diagnostic upper port plug

Sato, Kazuyoshi; Omori, Junji; Kondoh, Takashi; Hatae, Takaki; Kajita, Shin*; Ishikawa, Masao; Neyatani, Yuzuru; Ebisawa, Katsuyuki*; Kusama, Yoshinori

Fusion Engineering and Design, 84(7-11), p.1713 - 1715, 2009/06

 Times Cited Count:1 Percentile:10.95(Nuclear Science & Technology)

Engineering analyses have been performed for the representative diagnostic upper port plug of ITER. Maintenance and integration design have been also carried out for the diagnostic components to be installed in the upper port plug. From the electromagnetic and structural analyses, it has come up an important problem to suppress the displacement of the upper port plug rather than to reduce the produced stress. Reducing the EM force will help to decrease the severity of potential displacement. Maximum displacement of the port plug decreases with increasing in the number of slits in a manner that the displacement would seem to be less than the design tolerance. A proposed low body roller and inner frame may enhance maintenance and integration. These studies and designs have established the design basis for the diagnostic upper port plug.

Journal Articles

Design study of polychromators for ITER edge Thomson scattering diagnostics

Kajita, Shin; Hatae, Takaki; Kusama, Yoshinori

Review of Scientific Instruments, 79(10), p.10E726_1 - 10E726_4, 2008/10

 Times Cited Count:3 Percentile:20.5(Instruments & Instrumentation)

In ITER edge Thomson scattering measurement system, it is planned that polychromator by use of optical filters and avalanche photodiodes is used for the detection system. In this paper, the optimization of the filter transmission wavelength ranges is performed by minimizing the numerically calculated electron temperature error. The Thomson spectrum extends to considerably low wavelength ranges because high electron temperature measurement is required; therefore, it is important to eliminate the line emission from the plasma. It has been found that a filter below 656 nm, which corresponds to the strong line emission of $$D$$$$_{alpha}$$, is important for evaluating the electron density and temperature because the required maximum temperature is 10 keV, in which the tail of the spectrum is broadened around 400 nm. Moreover, the calculation indicates that a filter, transmission wavelength of which is higher than 1064 nm, is also useful to reduce the measurement error.

Journal Articles

Assessment of laser transmission mirror materials for ITER edge Thomson scattering diagnostics

Kajita, Shin; Hatae, Takaki; Voitsenya, V.*

Plasma and Fusion Research (Internet), 3, p.032_1 - 032_7, 2008/06

Assessment of in-vessel metallic mirror material for laser transmission used in ITER edge Thomson scattering diagnostics is done. Transient temperature increase due to the laser pulse irradiation to the laser transmission mirror is calculated by use of one-dimensional heat conduction equation. Based on the comparison between the numerical calculation and current data relevant to laser induced damage threshold (LIDT), the plausible material for the mirror is discussed. Because of its high reflectivity, gold, silver, copper are thought of as promising material. Necessary size for the laser transmission mirror for ITER edge Thomson scattering diagnostics is presented.

JAEA Reports

Design study of the optical system in the port plug for edge Thomson scattering diagnostics for ITER

Kajita, Shin; Hatae, Takaki; Katsunuma, Atsushi*; Kusama, Yoshinori

JAEA-Technology 2007-064, 60 Pages, 2008/01

JAEA-Technology-2007-064.pdf:5.65MB

The design of the collection optics for edge Thomson scattering diagnostics for ITER is provided. Since the neutron and $$gamma$$ ray radiation fluxes generated by the nuclear fusion reaction are considerably high near the plasma in ITER, available optical components are limited. Near the plasma, namely in the front-end optics, only metal mirrors can be used; moreover, optical fiber may be used only outside the vacuum window, which is located far from the front-end optics. In this design, three metal mirrors are used for the front-end optics, and the light ray is transmitted in the slender port plug through a relay optical system. To compensate the aberrations and increase the coupling efficiency to the fibers, two types of optical system with Catadioptric system are proposed for fiber-coupling optical system. It has been revealed that refraction type and reflection type system are not adequate for the fiber-coupling optical system. The image qualities are discussed based on the spot diagram and so on for the Catadioptric optical system.

Journal Articles

Plasma-assisted laser ablation of tungsten; Reduction in ablation power threshold due to bursting of holes/bubbles

Kajita, Shin; Ono, Noriyasu*; Takamura, Shuichi*; Sakaguchi, Wataru*; Nishijima, Dai*

Applied Physics Letters, 91(26), p.261501_1 - 261501_3, 2007/12

 Times Cited Count:39 Percentile:80.19(Physics, Applied)

Nanosecond laser ablation of tungsten (W) that was exposed to helium plasmas was investigated using optical emission spectroscopy. Sub-micrometor holes/bubbles are formed on the surface of W specimen when it was exposed to the helium plasma at sufficient higher temperature ($$ge$$ 1500-1600 K). The onset pulse energy to detect W I becomes $$sim$$ 0.2 J/cm$$^{-2}$$ after the W specimen was exposed to high-density helium plasmas, though the emission from a pure virgin W (before helium plasma irradiation) cannot be detected when the pulse energy was lower than 1 J/cm$$^{-2}$$. Laser-induced bursting of the holes/bubbles is suggested to be the physical mechanism leading to the significant reduction in the ablation power threshold.

Journal Articles

Comparison of He I line intensity ratio method and electrostatic probe for electron density and temperature measurements in NAGDIS-II

Kajita, Shin*; Ono, Noriyasu*; Takamura, Shuichi*; Nakano, Tomohide

Physics of Plasmas, 13(1), p.013301_1 - 013301_9, 2006/01

 Times Cited Count:49 Percentile:85.54(Physics, Fluids & Plasmas)

no abstracts in English

Oral presentation

Comparison of He I line intensity ratio method and electrostatic probe for electron density and temperature measurements

Kajita, Shin*; Ono, Noriyasu*; Okamoto, Masaaki*; Nakano, Tomohide; Takamura, Shuichi*

no journal, , 

no abstracts in English

Oral presentation

Experimental investigation of electron density and temperature measurement Using helium line intensity ratios in divertor simulator NAGDIS-II

Kajita, Shin*; Ono, Noriyasu*; Hiraishi, Takehiro*; Nakano, Tomohide; Takamura, Shuichi*

no journal, , 

no abstracts in English

Oral presentation

Measurement of electron temperature and density using He I line intensity ratio in tokamak plasmas

Hiraishi, Takehiro*; Okamoto, Masaaki*; Kajita, Shin*; Hasebe, Yu*; Ono, Noriyasu*; Takamura, Shuichi*; Nakano, Tomohide

no journal, , 

no abstracts in English

Oral presentation

Temporal evolution of electron temperature and density during ELM in JT-60 divertor plasma

Nakano, Tomohide; Asakura, Nobuyuki; Ono, Noriyasu*; Kajita, Shin*; Kawashima, Hisato; Kubo, Hirotaka; Shimizu, Katsuhiro; Fujimoto, Kayoko

no journal, , 

no abstracts in English

Oral presentation

Laser irradiation experiments to the tungsten surface having helium bubbles and holes

Kajita, Shin; Ono, Noriyasu*; Takamura, Shuichi*

no journal, , 

The effects of a transient heat load on damaged tungsten due to helium plasma irradiation have been investigated using a ruby laser with long pulse duration in the divertor simulator NAGDIS-II. Helium holes/bubbles, which were formed in the surface region of powder metallurgy tungsten due to the exposure to the helium plasma, disappeared after the laser pulse irradiation to the tungsten surface with sufficient pulse energy. When a tungsten coated graphite was exposed to the helium plasma, the surface was covered with arborescent nanostructured tungsten containing many helium bubbles inside the structure. Melting traces were found on the surface after the laser pulses irradiated the surface even though the pulse energy was sufficiently lower than that for melting bulk tungsten.

Oral presentation

Synergetic effects of plasma and pulse laser irradiation on tungsten material

Kajita, Shin

no journal, , 

no abstracts in English

Oral presentation

Study on a new business model which can be applied vitality of the private sector to backend system management in nuclear fuel cycle, 2; Assessment to social impacts and business risks by the developed model

Yoshida, Norimasa*; Kajita, Shingo*; Torii, Hiroyuki*; Hasegawa, Makoto; Ashida, Takashi

no journal, , 

Following to the previous presentation, an assessment to social impacts and business risks is carried out for the developed model. The framework of risk allocation and avoidance is also discussed.

32 (Records 1-20 displayed on this page)