• 제목/요약/키워드: Plasma Space

검색결과 456건 처리시간 0.03초

입자모사를 통한 HALL EFFECT THRUSTER의 플라즈마 운동 이해 (A VIEW PLASMA MOTION OF HALL EFFECT THRUSTER WITH PARTICLE SIMULATION)

  • 이재진;정성일;최원호;이종섭;임유봉;서미희;김형명
    • 한국우주과학회:학술대회논문집(한국우주과학회보)
    • /
    • 한국우주과학회 2007년도 한국우주과학회보 제16권2호
    • /
    • pp.139-143
    • /
    • 2007
  • 전기 추진시스템은 저렴한 개발비와 높은 신뢰성을 제공하는 추진 장치로 많은 분야에서 응용 되어 왔다. 특히 최근에 발사된 SMART-1과 MUSES-C는 우리에게 시사하는 바가 크다. 각각 European Space Agency(ESA)와 Japan Aerospace Exploration Agency(JAXA)에서 개발한 행성 탐사선으로, SMART-1은 달 탐사를 목적으로 하고 MUSES-C는 소행성 Itokawa의 토양을 채취해오는 것을 목적으로 한다. 이 두 탐사선에는 각각 Hall effect thruster와 Micro wave ion engine이 탑재되었는데, 작고 저렴한 비용의 탐사선을 이용해서 충분히 행성 탐사가 가능하다는 좋은 선례를 남겼다. 현재 개발되고 있는 과학기술위성 3호(STSAT-3)에도 전기추진 장치가 탑재되는데, SMART-1에 탑재 되었던 것과 유사한 Hall effect thruster가 인공위성 연구센터와 KAIST 물리학과의 GDPL과 공동으로 개발되고 있다. 성능이 좋은 전기 추력 장치를 개발하기 위해 추력기 내부에서 발생하는 플라즈마의 물리적 특성을 파악하는 것은 매우 중요한 일이다. 이 논문에서는 이러한 플라즈마의 특성을 모사하는 방법으로 Particle In Cell 모사와 더불어 독립적인 개개 입자의 운동을 기술하는 입자모사(particle simulation)를 이용하는 방법을 제시 하고자 한다. 이러한 접근 방법은 실제 전기추력장치를 설계하고 실험하는 담당자에게 플라즈마 운동에 대한 명료한 지식을 제공해 줄 수 있을 것으로 생각된다.

  • PDF

A Study on Virtual Studio Application using Microsoft Hololens

  • Lee, Jaehyun;Kim, Seunghyeon;Kim, Lyounghui;Kang, Jinwook;Lee, Seunghyun;Kwon, Soonchul
    • International journal of advanced smart convergence
    • /
    • 제6권4호
    • /
    • pp.80-87
    • /
    • 2017
  • Mixed Reality (MR) shows a composite image of a virtual object in the real world. It has been applied to various fields by the introduction of head mounted display (HMD) such as Microsoft's Hololens [1-3]. The virtual studio in broadcasting combines the contents created by computer graphics with the actual set to reproduce the 3D image screen. This requires physical space such as a set of chroma keys. It also requires professional knowledge and manpower and costly equipment to post-process the graphics and information for long periods of time. Therefore, in this paper, we aim to study the implementation of virtual studio based on Mixed Reality using Microsoft Hololens. Through the implementation of 'Holo-studio' application, realistic and virtual objects of broadcasting camera viewpoint were acquired at the same time. Using Microsoft's spectator view library, the frame rate is degraded in objects with high polygons (100,000 polygons). The proposed method maintains 60 fps image transmission in high polygon objects. The results of this paper show the possibility of using virtual studio at low cost which does not need separate physical space.

논문 : 플라즈마 펄스 추력기를 이용한 인공위성 자세제어 기법 연구 (Papers : Feasibility Study on Attitude Control of Spacecraft Using Pulsed Plasma Thrusters)

  • 지효선;이호일;이훈구;탁민제
    • 한국항공우주학회지
    • /
    • 제30권3호
    • /
    • pp.46-56
    • /
    • 2002
  • 본 논문에서는 플라즈마 펄스 추력기(PPT)를 사용한 우주 비행체의 자세 제어 가용성을 연구하였다. 전형적인 기체 추진 시스템에 비해 PPT는 높은 임펄스 특성을 갖고 있어 궤도나 자세 제어에 필요한 추진제의 질량을 적게 소모한다. PPT는 상대적으로 긴 작동 시간과 장착의 간편성 때문에 장기 작동을 요구하는 임무에 많이 적용되리라 기대된다. 소형 위성 시스템의 자세 제어를 위한 PPT의 적용 가능성을 실제 임무를 통하여 연구하였다. 고전적인 비례 미분 제어기와 퍼지 제어기를 적용해 보았고 점 더 유연한 임무 성능을 위해 연료 절감형 퍼지 제어기를 제안하였다.

Intrusion of a Magnetic Field through the Overlying Field in the Solar Atmosphere Induced by Ballooning Instability

  • 전홍달;최광선
    • 천문학회보
    • /
    • 제35권1호
    • /
    • pp.26.2-26.2
    • /
    • 2010
  • It has been a puzzle in solar physics how a low-lying magnetic structure such as a solar prominence surrounded by a strongly line-tied overlying field sometimes intrudes through the latter and goes into eruption. A numerical simulation study of the solar coronal plasma reveals that a ballooning instability can explain this type of eruptive process. We consider an idealized situation with two flux ropes merging. When magnetic field lines from different flux ropes reconnect, a new field line connecting farther footpoints is generated. Since the field line length abruptly increases, the field line expands outward. If the plasma beta is low, this expansion takes place more or less evenly over the whole field line. If, on the other hand, the plasma beta is high enough somewhere in this field line, the outward expansion is not even, but is localized as in a bulging balloon. This ballooning section of the magnetic field penetrates out of the overlying field, and eventually the originally underlying field and the overlying field come to interchange their apex positions. This process may explain how a field structure that has stably been confined by an overlying field can occasionally show a localized eruptive behavior.

  • PDF

A Study on the Temporal Behavior of the Wall Voltage in a surface-type AC panel

  • Kim, Jung-Hun;Lee, Jun-Hak;Choi, Young-Wook;Whang, Ki-Woong
    • 한국정보디스플레이학회:학술대회논문집
    • /
    • 한국정보디스플레이학회 2000년도 제1회 학술대회 논문집
    • /
    • pp.175-176
    • /
    • 2000
  • Electric fields and the wall voltages in a surface-type AC PDP cell were measured using a Laser Induced Fluorescence Spectroscopy. For the condition of He 100Torr, 200V sustain voltage and 50kHz sustain frequency, the wall voltage dropped from about 50V to about -75V within $1{\mu}sec$ after the main discharge. And the wall voltage decreased with the rate of $10.8V/{\mu}sec$ due to the accumulation of the space charges after $1{\mu}sec$. But when the operating pressure was 40Torr, it increased with the rate of $4.5V/{\mu}sec$ because the diffusion effect of the wall charge on MgO surface was more dominant than the accumulation effect of the space charges. During the pulse-off period, the wall voltage decreased slightly due to the diffusion of the wall charge. When the sustain voltage was 250V, the self-erasing discharge occurred, and the absolute value of the wall voltage decreased rapidly just after the pulses were off, which was caused by the accumulation of the charges generated by the self-erasing discharge.

  • PDF

Physics of Solar Flares

  • Magara, Tetsuya
    • 한국우주과학회:학술대회논문집(한국우주과학회보)
    • /
    • 한국우주과학회 2010년도 한국우주과학회보 제19권1호
    • /
    • pp.25.1-25.1
    • /
    • 2010
  • This talk outlines the current understanding of solar flares, mainly focusing on magnetohydrodynamic (MHD) processes. A flare causes plasma heating, mass ejection, and particle acceleration that generates high-energy particles. The key physical processes related to a flare are: the emergence of magnetic field from the solar interior to the solar atmosphere (flux emergence), formation of current-concentrated areas (current sheets) in the corona, and magnetic reconnection proceeding in current sheets that causes shock heating, mass ejection, and particle acceleration. A flare starts with the dissipation of electric currents in the corona, followed by various dynamic processes which affect lower atmospheres such as the chromosphere and photosphere. In order to understand the physical mechanism for producing a flare, theoretical modeling has been developed, in which numerical simulation is a strong tool reproducing the time-dependent, nonlinear evolution of plasma before and after the onset of a flare. In this talk we review various models of a flare proposed so far, explaining key features of these models. We show observed properties of flares, and then discuss the processes of energy build-up, release, and transport, all of which are responsible for producing a flare. We come to a concluding view that flares are the manifestation of recovering and ejecting processes of a global magnetic flux tube in the solar atmosphere, which was disrupted via interaction with convective plasma while it was rising through the convection zone.

  • PDF

Exhaust Plasma Characteristics of Direct-Current Arcjet Thrusters

  • Tahara, Hirokazu
    • 한국추진공학회:학술대회논문집
    • /
    • 한국추진공학회 2004년도 제22회 춘계학술대회논문집
    • /
    • pp.327-334
    • /
    • 2004
  • Spectroscopic and electrostatic probe measurements were made to examine plasma characteristics with or without a metal plate for a 10-㎾-class direct-current arcjet Heat fluxes into the plate from the plasma were also evaluated with a Nickel slug and thermocouple arrangement. Ammonia and mixtures of nitrogen and hydrogen were used. The NH$_3$ and $N_2$+3H$_2$ plasmas in the nozzle and in the downstream plume without a plate were in thermodynamical nonequilibrium states. As a result, the H-atom electronic excitation temperature and the $N_2$ molecule-rotational excitation temperature intensively decreased downstream in the nozzle although the NH molecule-rotational excitation temperature did not show an axial decrease. Each temperature was kept in a small range in the plume without a plate except for the NH rotational temperature for NH$_3$ gas. On the other hand, as approaching the plate, the thermodynamical nonequilibrium plasma came to be a temperature-equilibrium one because the plasma flow tended to stagnate in front of the plate. The electron temperature had a small radial variation near the plate. Both the electron number density and the heat flux decreased radially outward, and an increase in H$_2$ mole fraction raised them at a constant radial position. In cases with NH$_3$ and $N_2$+3H$_2$ a large number of NH radical with a radially wide distribution was considered to cause a large amount of energy loss, i.e., frozen flow loss, for arcjet thrusters.

  • PDF

The First Report on the Afternoon E-Region Plasma Density Irregularities in Middle Latitude

  • Yang, Tae-Yong;Kwak, Young-Sil;Lee, Jaewook;Park, Jaeheung;Choi, Seonghwan
    • Journal of Astronomy and Space Sciences
    • /
    • 제38권2호
    • /
    • pp.135-143
    • /
    • 2021
  • We report, for the first time, the afternoon (i.e., from noon to sunset time) observations of the northern mid-latitude E-region field-aligned irregularities (FAIs) made by the very high frequency (VHF) coherent backscatter radar operated continuously since 29 December 2009 at Daejeon (36.18°N, 127.14°E, 26.7°N dip latitude) in South Korea. We present the statistical characteristics of the mid-latitude afternoon E-region FAIs based on the continuous radar observations. Echo signal-to-noise ratio (SNR) of the afternoon E-region FAIs is found to be as high as 35 dB, mostly occurring around 100-135 km altitudes. Most spectral widths of the afternoon echoes are close to zero, indicating that the irregularities during the afternoon time are not related to turbulent plasma motions. The occurrence of afternoon E-regional FAI is observed with significant seasonal variation, with a maximum in summer and a minimum in winter. Furthermore, to investigate the afternoon E-region FAIs-Sporadic E (Es) relationship, the FAIs have also been compared with Es parameters based on observations made from an ionosonde located at Icheon (37.14°N, 127.54°E, 27.7°N dip latitude), which is 100 km north of Daejeon. The virtual height of Es (h'Es) is mainly in the height range of 105 km to 110 km, which is 5 km to 10 km greater than the bottom of the FAI. There is no relationship between the FAI SNR and the highest frequencies (ftEs) (or blanket frequencies (fbEs)). SNR of FAIs, however, is found to be related well with (ftEs-fbEs).

태양 활동과 대서양 지역에서 발생하는 equatorial plasma bubble 사이의 상호 관계

  • 이재진;민경욱
    • 한국우주과학회:학술대회논문집(한국우주과학회보)
    • /
    • 한국우주과학회 2003년도 한국우주과학회보 제12권2호
    • /
    • pp.31-31
    • /
    • 2003
  • Equatorial Plasma Bubble(EPB)은 적도 지역에서 Rayleigh-Taylor Instability에 의해 발생하는 이온층 플라즈마의 불안정성 현상으로, 주변의 플라즈마 밀도에 비해 좁은 영역에서 플라즈마 밀도가 급격하게 떨어지는 현상을 말한다. 지역적으로 보면, 겨울철에는 대서양 지역에서 집중적으로 발생하고 여름철에서는 태평양 지역에서 많이 관측된다. 이러한 불안정 현상은 단파 통신 장애를 유발할 수 있기 때문에 많은 연구 대상이 되어왔지만, 아직까지 태양 활동이나 지자기 변화에 의한 상호 연관성이 규명되지 못 하고 있다. 이것은 Rayleigh-Taylor Instability를 발생시키는 여러 인자들이 매우 복잡하게 관련되어 있기 때문인데, 본 연구에서는 특정 지역에서 발생하는 EPB에 한정하여 태양 활동과의 상호 연관성에 대해 분석하고자 하였다. 또한 단순한 발생 빈도에 대한 통계적인 처리가 아닌, EPB하나 하나에 대한 특성을 분석함으로써 EPB의 발생과 관련한 보다 명확한 분석이 가능하게 되었다. 분석에 필요한 data는 KOMPSAT-1의 Langmuir Probe(LP)에 의해 2000년에서 2001년 사이에 얻은 이온층의 전자 밀도를 사용하였는데, KOMPSAT-1의 LP는 같은 기간 활동한 다른 위성에 비해 좋은 시간 분해능을 가지고 있기 때문에 EPB의 통계 처리에 적당한 것으로 생각되었다.

  • PDF

THEORY AND SIMULATION OF BROADBAND ELECTROSTATIC NOISE IN THE MAGNETOTAIL

  • Kim, S.Y.
    • Journal of Astronomy and Space Sciences
    • /
    • 제11권2호
    • /
    • pp.250-272
    • /
    • 1994
  • Various plasma instabilities driven by the ion beams have been proposed in order to explain the broadband electrostatic noise (BEN) in the earth's geomagnetic tail. Ion acoustic, ion-ion two stream, and electron acoustic instabilities have been proposed. Here we consider a theoretical investigation of the generation of BEN by cold streaming ion beams in the earth's magnetotail. Linear theory analysis and particle simulation studies for the plasma sheet, which consists of warm electrons and ions as well as cold streaming ion beams, have been done. Both beam-ion acoustic and ion-ion two stream instabilities easily occur when the beam and warm electron temperature ratio, $T_b/T_e$ is small enough. The numerical simulation results confirm the existence of broadband electrostatic noise whose frequency is ranged from $\omega$=0 to $\omega$$\omega_{pe}$.

  • PDF