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真空容器内でのシリカダスト浮遊の実験的研究およびマイクロキャビティ内での帯電と表面電界によって浮遊する月砂高度の予測
https://doi.org/10.18997/00007309
https://doi.org/10.18997/000073097a9c7d64-9d52-49aa-908b-70f4ef19a4dd
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kou_k_460.pdf (8.5 MB)
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Item type | 学位論文 = Thesis or Dissertation(1) | |||||||
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公開日 | 2019-08-02 | |||||||
資源タイプ | ||||||||
資源タイプ識別子 | http://purl.org/coar/resource_type/c_db06 | |||||||
資源タイプ | doctoral thesis | |||||||
タイトル | ||||||||
タイトル | Experimental Investigation on Silica Dust Lofting in the Vacuum Chamber and Predictions of Lunar Dust Heights due to Charging within Micro-Cavities and Surface Electric Field | |||||||
言語 | en | |||||||
タイトル | ||||||||
タイトル | 真空容器内でのシリカダスト浮遊の実験的研究およびマイクロキャビティ内での帯電と表面電界によって浮遊する月砂高度の予測 | |||||||
言語 | ja | |||||||
言語 | ||||||||
言語 | eng | |||||||
著者 |
Orger, Necmi Cihan
× Orger, Necmi Cihan
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抄録 | ||||||||
内容記述タイプ | Abstract | |||||||
内容記述 | There is a soil-like layer above the bedrock of the Moon that is produced by the small meteoroid impacts on the lunar surface, which is also called as the lunar regolith. The size of the regolith particles ranges from several centimeters to submicron size, and the small-scale particles are also referred as the lunar dust, which can be transported by the electrostatic forces above the lunar surface. Electrostatically lofted and/or levitated dust grains were detected while scattering the sunlight above the lunar terminator region, and this physical phenomenon has been called the lunar horizon glow (LHG). TV cameras of Surveyor missions first monitored the LHG in 1966 and 1968, and the excessive brightness to coronal and zodiacal light (CZL) indicated that the dust population was considerably denser than the levels that can be produced by micrometeorite ejecta on the lunar surface. In addition, all observations of the LHG were under the solar wind plasma, and the lunar surface directly interacts with the charged particles in the absence of a global magnetic field and a dense atmosphere. Even though the solar wind plasma has a lower temperature and higher density than the magnetospheric plasma, enhanced fluxes of charged particles can be observed in some cases such as solar energetic particle events or coronal mass ejections (CMEs). In this research, the purpose can be described as (1) predicting the maximum height variation of the dust grains above the lunar terminator under various ambient plasma conditions and (2) experimentally investigating the silica dust lofting in the vacuum chamber under the electron beam. Therefore, the equations that are used in the simulations are compared to the experimental results, and the significance of the surface parameters such as the presence of the horizontal electric field and the increased packing density on the electrostatical dust launching are investigated as well. The LHG observations, the lunar dust exosphere measurements, and the previous studies on the lunar dust simulations and experiments are presented in chapter 1. In addition, the simulation method of the lunar surface charging and the results of the surface potential, the electric field and Debye length are discussed for the plasma parameters of the regular solar wind and three selected geoeffective CME events in chapter 2. In chapter 3, the initial separation of the dust particles and the maximum height calculations are presented in detail. The simulation results show that the surface potential is highly variable on the lunar terminator region, and the dust launching rates are significantly controlled by the secondary electron emission and the dust sizes. Even though the micron-sized dust grains are launched from the surface more frequently than the submicron-sized dust particles, their heights are less influenced by the surface electric field in all cases. The simulations are performed for the dust particles with 0.1, 1 and 5 μm radius, and the uncertainty range of the height predictions are represented as well. In chapter 4, the experiments on the silica dust grains are explained in detail. The experiments are performed under 4×10-3 Pa pressure in a general-purpose vacuum chamber. In addition, an electron beam is produced from a cathode ray tube, and the electron current density is measured as approximately 2.87×10-4 Am-2. Different from the previous dust lofting experiments, the initial launching velocities of the grains are detected by the microscopic telescope and the high-speed camera by focusing on the near-surface area above the dust sample. Three different types of experiments are performed on the silica dust grains. First, the dust grains are loaded on the graphite plate without applying additional pressure or external horizontal electric field during the experiment. Therefore, it is called the simple case, and the measurements are compared with the estimated values. Second, the separate dust samples are compressed after loading on to the graphite plate with approximately 781 and 3780 Pa in order to increase the contact surface areas among the dust grains while decreasing the number of the microcavities. Third, the graphite plate is placed between two parallel aluminum plates that are separated by 5 and 12 cm distance and biased to 240 V in both cases. Therefore, it is expected to increase the number of the rolling particles over the surface while increasing the number of the inter-particle collisions. Finally, all of the results are discussed for the simulations and the experiments in chapter 5. First, the dust grains with 5 μm radius reach significantly similar heights with the LHG observations of Surveyor mission in the simulations. Second, the dust grains 0.1 μm in radius are lofted to the heights similar to the Lunokhod-2 astrophotometer observations under the regular solar wind. Third, the laboratory experiments point out that several factors are determinative to estimate the dust lofting such as the contact surface areas between the dust grains, the packing density, the existence of the microcavities, and the inter-particle collisions in the presence of the horizontal electric field. Most of the particles are launched within the estimated range for the simple case. Furthermore, increased packing density reduces the number of the lofted dust grains; however, their vertical launching velocities are increased due to stronger electrostatic potential energy built-up between the dust grains. In addition, strong horizontal electric field contributes to the dust release from the surface by potentially increasing the inter-particle collisions; and the current results suggest lower launching velocities than the previous cases. Finally, the aggregates are lofted as well as the single particles, and some of them separated during the lofting motion. Therefore, the separation of charged dust grains on the flight can be an additional source for the smaller grains. In chapter 6, the conclusions and the recommendations are explained, and the future tasks are determined as the investigation of the correlation between the micrometeorite impact regions and the electrostatic transportation of the dust grains. | |||||||
目次 | ||||||||
内容記述タイプ | Other | |||||||
内容記述 | 1 Introduction||2 Lunar Surface Charging Simulations||3 Electrostatic Lunar Dust Transportation||4 Experimental Investigation on Silica Dust Lofting||5 Discussion||6 Conclusions and Recommendations | |||||||
備考 | ||||||||
内容記述タイプ | Other | |||||||
内容記述 | 九州工業大学博士学位論文 学位記番号:工博甲第460号 学位授与年月日:平成30年9月21日 | |||||||
キーワード | ||||||||
主題Scheme | Other | |||||||
主題 | Lunar dust | |||||||
キーワード | ||||||||
主題Scheme | Other | |||||||
主題 | Dust lofting | |||||||
キーワード | ||||||||
主題Scheme | Other | |||||||
主題 | Lunar surface charging | |||||||
キーワード | ||||||||
主題Scheme | Other | |||||||
主題 | Electrostatic dust motion | |||||||
キーワード | ||||||||
主題Scheme | Other | |||||||
主題 | Lunar horizon glow | |||||||
アドバイザー | ||||||||
値 | 豊田, 和弘 | |||||||
学位授与番号 | ||||||||
学位授与番号 | 甲第460号 | |||||||
学位名 | ||||||||
学位名 | 博士(工学) | |||||||
学位授与年月日 | ||||||||
学位授与年月日 | 2018-09-21 | |||||||
学位授与機関 | ||||||||
学位授与機関識別子Scheme | kakenhi | |||||||
学位授与機関識別子 | 17104 | |||||||
学位授与機関名 | 九州工業大学 | |||||||
学位授与年度 | ||||||||
内容記述タイプ | Other | |||||||
内容記述 | 平成30年度 | |||||||
出版タイプ | ||||||||
出版タイプ | VoR | |||||||
出版タイプResource | http://purl.org/coar/version/c_970fb48d4fbd8a85 | |||||||
アクセス権 | ||||||||
アクセス権 | open access | |||||||
アクセス権URI | http://purl.org/coar/access_right/c_abf2 | |||||||
ID登録 | ||||||||
ID登録 | 10.18997/00007309 | |||||||
ID登録タイプ | JaLC |