| Project/Area Number |
17K17764
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| Research Category |
Grant-in-Aid for Young Scientists (B)
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| Allocation Type | Multi-year Fund |
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| Research Field |
Aerospace engineering
Plasma science
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| Research Institution | University of Fukui |
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Principal Investigator |
Fukunari Masafumi 福井大学, 遠赤外領域開発研究センター, 助教 (80786070)
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| Project Period (FY) |
2017-04-01 – 2020-03-31
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| Project Status |
Completed (Fiscal Year 2019)
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| Budget Amount *help |
¥4,420,000 (Direct Cost: ¥3,400,000、Indirect Cost: ¥1,020,000)
Fiscal Year 2019: ¥910,000 (Direct Cost: ¥700,000、Indirect Cost: ¥210,000)
Fiscal Year 2018: ¥1,430,000 (Direct Cost: ¥1,100,000、Indirect Cost: ¥330,000)
Fiscal Year 2017: ¥2,080,000 (Direct Cost: ¥1,600,000、Indirect Cost: ¥480,000)
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| Keywords | ミリ波放電 / 自己組織化 / ジャイロトロン / プラズマ計測 / マイクロ波ロケット / シャドウグラフ / 衝撃波 / ミリ波 / ガス放電 / 大気放電 / ハイスピードカメラ |
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| Outline of Final Research Achievements |
The beamed energy propulsions are attractive for the future low-cost mass-transportation to the space as alternatives to the chemical propulsions. A mega-watt class oscillator, gyrotron is currently available in the millimeter-wave range. The millimeter-wave discharge is a key factor of the thrust generation process. The ionization front propagates in the electric field lower than the ionization threshold and self-organized filamentary structures are created in the discharge. In this study, we investigated the millimeter wave discharge with high spatial and time resolution using a 303 GHz high-power gyrotron as a beam source. We observed the transition between two types of filamentary plasma arrays from the quarter-of-the-wavelength (λ/4) structure at the focal point to the comb-shaped array parallel to the incident beam with spacing of 0.96 λ for the first time. In addition, the shock wave formation and propagation was visualized by the shadowgraph.
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| Academic Significance and Societal Importance of the Research Achievements |
ミリ波放電で現れる自己組織化された構造は気体の電離閾値に比べミリ波の局所電界強度が高い超臨界条件(着火部)と、低い亜臨界条件で異なる。亜臨界条件でのミリ波放電は既存の電離モデルでは説明できず、また衝撃波通過後のガスを電離波面が進展するので複雑である。本研究ではミリ波放電が着火部の超臨界条件から亜臨界条件に遷移していく過程を観測した。この観測結果を通して、プラズマ表面での回折波が櫛状の放電構造を形成することを示した。さらにシャドウグラフにより同条件におけるプラズマ周辺での衝撃波形成過程を捉えた。これらのデータはミリ波ビーミング推進にとって重要なミリ波放電の電離モデル開発に寄与する。
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