• 제목/요약/키워드: Plasma Space

검색결과 456건 처리시간 0.027초

MAGNETIC FLUX-CURRENT SURFACES OF MAGNETOHYDROSTATIC EQUILIBRIA

  • Choe, G.S.;Jang, Minhwan
    • 천문학회지
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    • 제46권6호
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    • pp.261-268
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    • 2013
  • Magnetohydrostatic equilibria, in which the Lorentz force, the plasma pressure force and the gravitational force balance out to zero, are widely adopted as the zeroth order states of many astrophysical plasma structures. A magnetic flux-current surface is a surface, in which both magnetic field lines and current lines lie. We for the first time derive the necessary and sufficient condition for existence of magnetic flux-current surfaces in magnetohydrostatic equilibria. It is also shown that the existence of flux-current surfaces is a necessary (but not sufficient) condition for the ratio of gravity-aligned components of current density and magnetic field to be constant along each field line. However, its necessary and sufficient condition is found to be very restrictive. This finding gives a significant constraint in modeling solar coronal magnetic fields as force-free fields using photospheric magnetic field observations.

Global Magnetohydrodynamic Simulation of a Comet : When a Comet Crosses a Heliopheric Sector Boundary

  • Yu, Yi
    • International Union of Geodesy and Geophysics Korean Journal of Geophysical Research
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    • 제22권1호
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    • pp.6-23
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    • 1994
  • A disconnection event (DE) of the cometary plasma tail is one of most spectacular phenomena observed in comets. Yet, for years it has remained one of the great unsolved problems I astronomy and space physics. The solar wind is thought to play a major role in the creation of comet plasma tail (type Ⅰ) disconnection events. The goal of this paper is to present a mechanism that explains the disconnection event in terms of the local conditions at the comet. Comparison of the solar wind conditions and 16 DEs in Halley's comet shows that DEs are associated primarily with crossings of the heliospheric sector boundary and apparently not with any other properties of the solar wind, such as a high speed stream[Yi et al., 1994]. A 3-dimensional resistive magnetohydrodynamic simulation in this paper supports this association by showing that only front-side magnetic reconnection between the reversed interplanetary magnetic fields that exist when a comet crosses the heliospheric sector boundary [Niedner and Brandt, 1978] could reproduce the morphology of a DE, including ray formation [Brandt, 1982].

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Spatiotemporal Behaviors of Excited Xenon Atoms in a Three-Dimensional Diagnosable Microplasma Unit Cell with High Sustain Frequency for Plasma Display Panels

  • Oh, Jun-Seok;Sakai, Osamu;Hashimoto, Masaki;Tachibana, Kunihide
    • 한국정보디스플레이학회:학술대회논문집
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    • 한국정보디스플레이학회 2006년도 6th International Meeting on Information Display
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    • pp.925-928
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    • 2006
  • With the high sustain frequency at 250 kHz, a three-dimensional diagnostics of excited xenon atoms was investigated by the emission and absorption microscopic spectroscopy for plasma display panels, spatiotemporally. As a typical feature of the emissions, a broad discharge peak was observed on the temporal cathode and a sharp one was monitored on the anode, at the high frequency. However, the discharge starts from the cathode edge, actually, that is a discharge space on the floated address (or data) electrode. Spatially, the dense emission and absorption peak were observed in the discharge space between the sustain electrodes gap. Overall, the microdischarge at high sustain frequency showed priming dominant characteristics.

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무거운 이온을 포함하고 있는 플라스마에서 Pseudo-Potential Method와 1d PIC Simulation

  • 최정림;민경욱;이대영;라기철;이동렬;유창모
    • 한국우주과학회:학술대회논문집(한국우주과학회보)
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    • 한국우주과학회 2009년도 한국우주과학회보 제18권2호
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    • pp.43.4-44
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    • 2009
  • electron, ion, heavy ion으로 구성 된 plasma에서 hump type과 kink type(double layer)의 electrostatic solitary waves이 존재할 수 있다는 것을 pseudopotential method를 이용한 결과와 1d PIC(Particle-In-Cell) simulation method의 결과에서 각각 확인하였다. 1d PIC simulation에서 초기에 각각의 입자 종(species; electron, ion, heavy ion)의 밀도섭동(density perturbation)은 Gaussian 형태로 주었으며, 각각의 입자들의 drift velocity는 각각의 plasma 입자 종들의 thermal velocity로 나란한 방향으로 주었다.

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아크 플라즈마 유동에 삽입된 엔탈피 탐침의 동작특성 실험 (Experimental analysis on the characteristics of enthalpy probe immersed in arc plasma flow)

  • 서준호;남준석;최성만;홍봉근;홍상희
    • 한국항공우주학회지
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    • 제38권12호
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    • pp.1240-1246
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    • 2010
  • 내경 1.5 mm, 외경 4.8 mm를 갖는 엔탈피 탐침을 설계 제작하고, 17 kW급 비이송식 직류 아크히터로부터 나오는 고엔탈피 Ar 아크 플라즈마 유동의 중심축을 따라 삽입하면서 탐침 첨두가 파괴될 때까지 온도와 속도를 측정하였다. 이 실험으로부터, 설계된 엔탈피 탐침은 대기압 조건에서 최대 12,000 K 의 온도와 600 m/s 의 속도를 갖는 고엔탈피아크 플라즈마 유동장에 대해 탐침 첨두의 파괴 없이 동작할 수 있음을 관찰하였다. 탐침첨두에서 형성되는 비압축성 열경계층 및 열속 방정식으로부터 이 경우의 아크 플라즈마 유동은 약 ${\sim}5{\times}10^7\;W/m^2$의 열속 부하를 전달한 것으로 추측되었다. 이로부터, 설계된 엔탈피 탐침은 $0{\sim}5{\times}10^7\;W/m^2$의 열속 범위 내에서 다양한 형태의 아크히터로부터 발생되는 넓은 범위의 플라즈마 온도, 속도 및 농도를 동시에 측정할 수 있을 것으로 기대된다.

Magnetic Turbulence Associated with Magnetic Dipolarizations in the Near-Tail of the Earth's Magnetosphere: Test of Anisotropy

  • Lee, Ji-Hee;Lee, Dae-Young;Park, Mi-Young;Kim, Kyung-Chan;Kim, Hyun-Sook
    • Journal of Astronomy and Space Sciences
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    • 제28권2호
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    • pp.117-122
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    • 2011
  • In this paper, the anisotropic nature of the magnetic turbulence associated with magnetic dipolarizations in the Earth's plasma sheet is examined. Specifically, we determine the power spectral indices for the perpendicular and parallel components of the fluctuating magnetic field with respect to the background magnetic field, and compare them in order to identify possible anisotropic features. For this study, we identify a total of 47 dipolarization events in February 2008 using the magnetic field data observed by the THEMIS A, D and E satellites when they are situated near the neutral sheet in the near-Earth tail. For the identified events, we estimate the spectral indices for the frequency range from 1.3 mHz to 42 mHz. The results show that the degree of anisotropy, as defined by the ratio of the spectral index of the perpendicular components to that of the parallel component, can range from ~0.2 to ~2.6, and there are more events associated with the ratio greater than unity (i.e., the perpendicular index being greater than the parallel index) than those which are anisotropic in the opposite sense. This implies that the dipolarization-associated turbulence of the magnetic field is often anisotropic, to some non-negligible degree. We then discuss how this result differs from what the theory of homogeneous, anisotropic, magnetohydrodynamic turbulence would predict.

Effect of Microstructure on the Environmentally Induced Cracking Behavior of Al-Zn-Mg-Cu-Zr Aluminum Alloy

  • Ghosh, Rahul;Venugopal, A.;Pradeep, PI;krishna, L. Rama;Narayanan, P. Ramesh;Pant, Bhanu;Cherian, Roy M
    • Corrosion Science and Technology
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    • 제17권3호
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    • pp.101-108
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    • 2018
  • AA7010 is an Al-Zn-Mg-Cu alloy containing Zr, developed as an alternate to traditional AA7075 alloy owing to their high strength combined with better fracture toughness. It is necessary to improve the corrosion resistance and surface properties of the alloy by incorporating plasma electrolytic oxidation (PEO) method. AA7010-T7452 aluminum alloy has been processed through the forging route with multi-stage working operations, and was coated with $10{\mu}m$ thick $Al_2O_3$ ceramic aluminina coating using the plasma electrolytic oxidation (PEO) method. The corrosion, stress corrosion cracking (SCC) and nano-mechanical behaviours were examined by means of potentiodynamic polarization, slow strain rate test (SSRT) and nano-indentation tests. The results indicated that the additional thermomechanical treatment during the forging process caused a fully recrystallized microstructure, which lead to the poor environmental cracking resistance of the alloy in 3.5% NaCl solution, despite the overaging treatment. Although the fabricated PEO coating improved general corrosion resistance, the brittle nature of the coating did not provide any improvement in SCC resistance of the alloy. However, the hardness and elastic modulus of the coating were significantly higher than the base alloy.

우주 자원 탐사를 위한 레이저 유도 플라즈마 분광분석법의 우주 환경에서의 특성 분석 (Characteristics of Laser-Induced Breakdown Spectroscopy (LIBS) at Space Environment for Space Resources Exploration)

  • 최수진;여재익
    • 한국항공우주학회지
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    • 제40권4호
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    • pp.346-353
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    • 2012
  • 레이저 조사 시 발생되는 플라즈마를 성분 분석에 이용하는 Laser-Induced Breakdown Spectroscopy(LIBS)는 우주 자원 탐사에 적합한 실시간 성분 분석 기술이다. LIBS 플라즈마의 특성은 주위 압력의 영향을 크게 받는다. 본 연구에서는 다양한 물성치를 갖는 일곱 가지 원소(C, Ti, Ni, Cu, Sn, Al, Zn)의 지속시간(lifetime)이 760 - $10^{-5}$ torr의 압력 범위에서 분석되었다. 압력이 낮아짐에 따라 탄소와 티타늄의 lifetime은 감소하였고, 그 밖의 원소들은 1 torr의 압력에서 가장 오랜 시간동안 검출되었다. 원소별 lifetime 결과를 통하여 낮은 압력 하에서 플라즈마의 특성과 원소별 끓는점 및 전기음성도의 관계를 규명하였다.

A Brief Introduction of Current and Future Magnetospheric Missions

  • Yukinaga Miyashita
    • 우주기술과 응용
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    • 제3권1호
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    • pp.1-25
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    • 2023
  • In this paper, I briefly introduce recently terminated, current, and future scientific spacecraft missions for in situ and remote-sensing observations of Earth's and other planetary magnetospheres as of February 2023. The spacecraft introduced here are Geotail, Cluster, Time History of Events and Macroscale Interactions during Substorms / Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon's Interaction with the Sun (THEMIS / ARTEMIS), Magnetospheric Multiscale (MMS), Exploration of energization and Radiation in Geospace (ERG), Cusp Plasma Imaging Detector (CuPID), and EQUilibriUm Lunar-Earth point 6U Spacecraft (EQUULEUS) for recently terminated or currently operated missions for Earth's magnetosphere; Lunar Environment Heliospheric X-ray Imager (LEXI), Gateway, Solar wind Magneto-sphere Ionosphere Link Explorer (SMILE), HelioSwarm, Solar-Terrestrial Observer for the Response of the Magnetosphere (STORM), Geostationary Transfer Orbit Satellite (GTOSat), GEOspace X-ray imager (GEO-X), Plasma Observatory, Magnetospheric Constellation (MagCon), self-Adaptive Magnetic reconnection Explorer (AME), and COnstellation of Radiation BElt Survey (CORBES) approved for launch or proposed for future missions for Earth's magnetosphere; BepiColombo for Mercury and Juno for Jupiter for current missions for planetary magnetospheres; Jupiter Icy Moons Explorer (JUICE) and Europa Clipper for Jupiter, Uranus Orbiter and Probe (UOP) for Uranus, and Neptune Odyssey for Neptune approved for launch or proposed for future missions for planetary magnetospheres. I discuss the recent trend and future direction of spacecraft missions as well as remaining challenges in magnetospheric research. I hope this paper will be a handy guide to the current status and trend of magnetospheric missions.

Statistical properties of the fast flows accompanied by dipolarization in the near-Earth tail

  • Kim, Hyun-Sook;Lee, Dae-Young;Ahn, Byung-Ho
    • 한국우주과학회:학술대회논문집(한국우주과학회보)
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    • 한국우주과학회 2010년도 한국우주과학회보 제19권1호
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    • pp.40.4-41
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    • 2010
  • Using magnetic field and plasma moment data obtained by THEMIS satellites(A, D, and E), we selected 203 fast flow events accompanied by dipolarization in the near-Earth region( X(GSM) = -7 ~ -12 RE) and statistically examined their properties. It was found that most of the fast flows show the maximum velocity between 1 minute before dipolarization onset and 2 minutes after onset and proceed earthward and duskward. We also found that only the flows with low velocity of less than 400 km/s are observed at X > -8 RE, while the high velocity flows(as well as low velocity flows) are observed at the further tailward region(X < -8 RE). And most of the tailward flows are slow regardless of distance at X(GSM) = -7 ~ -12 RE. On the other hand, if we consider the fast flow as a bubble (Pontius and Wolf, 1990), the entropy parameter, PV5/3 is an important factor to describe the plasma sheet dynamics. Thus we investigated the relationship between the flow velocity and the amount of change in PV5/3 before and after dipolarization onset and found out that the dipolarizations with more depleted entropy parameter tend to show higher flow velocity. Also we examined how the magnetic field at geosynchronous orbit responds to the fast flow accompanied by dipolarization in the near-earth plasma sheet, using the measurements from GOES 11 and 12 statellites. We found that most of the fast flows do not reach geosynchronous orbit as suggested by Ohtani et al. (2006).

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