2006 Fiscal Year Final Research Report Summary
Pulsed-laser ablation of hydrogen-dposited graphite target
| Project/Area Number |
17540468
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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 |
Plasma science
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| Research Institution | Osaka University |
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Principal Investigator |
SAKAWA Youichi Osaka University, Institute of Laser Engineering, Associate Professor, レーザーエネルギー学研究センター, 助教授 (70242881)
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| Co-Investigator(Kenkyū-buntansha) |
SHOJI Tatsuo Nagoya University, Graduate School of Engineering, Associate Professor, 工学研究科, 助教授 (50115581)
TANABE Tetsuo Kyusyu University, Interdisciplinary School of Engineering, Professor, 総合理工学研究院, 教授 (00029331)
YAMAZAKI Kouzou Nagoya University, Graduate School of Engineering, Professor, 工学研究科, 教授 (50115648)
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| Project Period (FY) |
2005 – 2006
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| Keywords | Laser ablation / Tritium removal / Graphite / Pulsed laser / Tokamak / Divertor |
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| Research Abstract |
Carbon materials are one of the candidates for plasma facing materials in ITER and nuclear-fusion reactors because of its superior nature at high-heat flux and low atomic number. However, when carbon is eroded by hydrogenic plasmas containing tritium, it co-deposits with tritium, and periodical removal is required from the safety reason. For the purpose of tritium removal from carbon co-deposits on plasma-facing material of fusion device, pulsed-laser induced desorption of hydrogen from co-deposits on JT-60 open-divertor tile has been investigated.
The fundamental (L=1064 nm) and fourth harmonic (L=266 nm) emission of Nd:YAG laser (laser energy <35 mJ/pulse for 1064 nm and <3 mJ/pulse for 266 nm, pulse duration 〜20 ps, I_L<6 x 10^<12> W/cm^2 for 1064 nm and 5 x 10^<11> W/cm^2 for 266 nm, repetition rate=10 Hz) were used.
Ablation depth per laser shot vs I_L showed that whereas the threshold laser intensity for ablation I_<ablation> 〜10^<10> W/cm^2 was nearly independent on L, the linear absorption-coefficient was larger for L=266 nm. A large difference in the threshold laser intensities of the strong ionization of carbon I_<ionization> between L=1064 and 266 nm was observed ; I_<ionization>= 9 x 10^<10> and (3.4〜7.4) x 10^<11>W/cm^2 for L=266 and 1064 nm, respectively. The lower I_<ionization> for L=266 nm was explained by three-photon ionization of carbon. Hydrogen-desorption efficiency, defined as the ratio between the number of desorbed hydrogen by laser irradiation and that of hydrogen retained in the ablated volume, was largest in the region, where strong ionization of C^+ occurred, and was larger for L=266 nm, in which a laser photon can cut C-H bond, compared with that for L=1064 nm. For the ablative removal of hydrogen, a short-wavelength and high-power laser is desirable.
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Research Products
(11 results)
