2005 Fiscal Year Final Research Report Summary
Up take and release characteristics of hydrogen isotopes in re-deposited layers on the plasma facing wall
| Project/Area Number |
16560720
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Nuclear fusion studies
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| Research Institution | Tohoku University |
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Principal Investigator |
NAGATA Shinji Tohoku University, Institute for Materials Research, Associate Professor, 金属材料研究所, 助教授 (40208012)
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| Co-Investigator(Kenkyū-buntansha) |
TSUCHIYA Bun Tohoku University, Institute for Materials Research, Research Associate, 金属材料研究所, 助手 (90302215)
TOH Kentaro Tohoku University, Institute for Materials Research, Research Associate, 金属材料研究所, 助手 (40344717)
SHIKAMA Tatsuo Tohoku University, Institute for Materials Research, Professor, 金属材料研究所, 教授 (30196365)
YAMAMOTO Shunya Japan Atomic Energy Agency, Takasaki Advanced Radiation Research Institute, Chief Researcher, 高崎量子応用研究所, 研究副主幹 (70354941)
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| Project Period (FY) |
2004 – 2005
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| Keywords | plasma facing materials / re-deposited layer / sputtering / tungsten / hydrogen isotopes / oxides / ion irradiation / optical properties |
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| Research Abstract |
In the present study, up-take, retention and release characteristics of hydrogen isotopes were studied on the W and Mo, which are promising candidates for plasma facing materials. W and Mo single crystalline disks were made by the floating zone melting method. As a simulation of the re-deposition layers, tungsten films were prepared by a conventional rf magnetron sputtering with a W target in defined Ar/O2 mixture, at a temperature range between 300 and 900 K. The micro structure of the deposited films strongly depended on the substrate temperature and oxygen concentration. The highly oriented films prepared at the substrate temperature above 800 K exhibit good gasochromic properties for hydrogen gas exposure. However, hydrogen retention was not significantly affected by the composition of oxides and the micro structure of the deposited layer. Hydrogen accumulation in W surface irradiated by noble gas ions was examined in connection with morphological and compositional changes. Remarkable hydrogen retention was found for the He and Xe ion implanted layers where blisters and exfoliation were created. Tungsten oxides such as WO2 were formed along projected ranges of the implanted ions. The results indicated that the porous oxide surface layers play an important role for dissociation of hydrogen, and hydrogen trapping is correlated with microstructural changes owing to the formation of bubbles and clusters of implanted noble gas atoms. Preferential up-take of H atoms was found in the He saturated layer, when the specimen was exposed to the atmosphere mainly containing D_2 and D_2O gas ; the up-take rate for H was an order of magnitude higher than that for D during D_2 gas exposure. The observed isotope effects on the up-take behavior might be due to the proton conductive oxides formed on the He irradiated surface of the W and Mo.
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