篠原 育

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Magneto Plasma Sail (MPS) is one of the next generation space propulsion systems which generates a propulsive force using the interaction between the solar wind plasma and an artificial inflated magnetosphere generated by a superconductive coil. In the MPS system, the magnetosphere as a sail must be inflated by the plasma injection from the spacecraft in order to obtain the thrust gain. In the present study, the magnetic inflation concept is numerically tested by so-called ion one-component plasma model. As a simulation result, the magnetic moment of the system is drastically increased up to 45 times that of the coil current at plasma-β = 20 and r_Li/L (radius of gyro motion / characteristics length of the magnetic field) = 0.01, and this is the first successful magnetosphere inflation obtained by numerical simulation. Corresponding maximum thrust gain is also estimated to be about 45.

Kinetic aspects of the ion current layer at the center of a reconnection outflow exhaust near the X-type region are investigated by a two-dimensional particle-in-cell (PIC) simulation. The layer consists of magnetized electrons and unmagnetized ions that carry a perpendicular electric current. The ion fluid appears to be nonideal, sub-Alfvenic, and nondissipative. The ion velocity distribution functions contain multiple populations, such as global Speiser ions, local Speiser ions, and trapped ions. The particle motion of the local Speiser ions in an appropriately rotated coordinate system explains the ion fluid properties very well. The trapped ions are the first demonstration of the regular orbits in the chaotic particle dynamics [Chen and Palmadesso, J. Geophys. Res. 91, 1499 (1986)] in self-consistent PIC simulations. They would be observational signatures in the ion current layer near reconnection sites. (C)C 2013 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.

A parallelized two-dimensional full particle-in-cell (PIC) simulations with an adaptive mesh refinement (AMR) technique for the interaction of solar wind with kinetic scale magnetosphere around a magnetic sail are conducted. For multi-scale simulations, the newly developed AMR-PIC code has a method to modify the grid size and time step interval of computational domain in the midst of the simulations temporally and locally. In the simulation results under the typical working condition introducing the AMR technique, it is shown that the direction of interplanetary magnetic field depend strongly on the magnetospheric configuration including electron dynamics and Alfven bow shock structure. Although more validation studies are needed, the AMR-PIC code shows the worth of development for multi-scale simulations.

A discretization procedure for a total variation diminishing (TVD) scheme is introduced to an electromagnetic hybrid particle-in-cell (PIC) plasma simulation code in order to improve the numerical stability and resolution when calculating the plasma flow field in which magnetic field discontinuities (for example, Rankine-Hugoniot jump conditions for shock waves) are generated. In the hybrid PIC code used in this study, ions are treated as particles and electrons are assumed to be an inertia-less (mass-less) fluid. In the numerical results of one-dimensional test simulations, the TVD scheme significantly prevents non-physical, numerical oscillations, which would ordinarily be produced in the solution when the convection term of the magnetic induction equation in the hybrid PIC code is discretized by central difference schemes at magnetic field discontinuities. Furthermore, a two-dimensional simulation of the global structure of a collision-less bow shock, which is suitable for practical use, makes it possible to clearly capture the bow shock by using the hybrid PIC code with the TVD scheme. (C) 2012 Elsevier B.V. All rights reserved.

Magnetic sail is a propellantless propulsion system used in space, which is capable of generating a propulsive force by the interaction between the magnetic field generated by a hoop coil and the solar wind plasma flow. Three dimensional hybrid (ion particles and electron fluid) particle-in-cell (PIC) simulation and scale-model experiment are performed to investigate the characteristics of the plasma flow around a magnetosphere on the ion inertial scale where an ion gyro radius rLi is comparable to the representative size of magnetosphere L. It is found that the dark region around magnetospheric boundary appearing in the experimental photograph corresponds to the region where the plasma density increases due to the plasma trapped by the magnetic field. The induced current which is both perpendicular to the plasma flow and the magnetic field also increases in the magnetospheric boundary region hence this region coincides with the magnetopause current layer. The width of the magnetopause current layer has a good agreement between the numerical simulation result and experimental result. Also, the predicted thrust value of 0.34 ± 0.01 N obtained by the hybrid simulation agrees well with the experimental result when numerical simulation is carried out by considering the ion-neutral collision effect. The hybrid PIC simulation carried out without considering the collisional effect gave a thrust value of 0.4 ± 0.01 N (increasing by a factor of 1.3), which can be applied to the thrust evaluation of the magnetic sail in a collisionless interplanetary space.

Solar wind plasma flow with interplanetary magnetic field (IMF) and the thrust of the magnetic sail are examined by time-dependent, two-dimensional, X-Y Cartesian, hybrid particle-in-cell (PIC) simulations. The hybrid-PIC simulation model is that the ions are treated kinetically as particles and the electrons are modeled as an inertia-less (mass-less) fluid. In this simulation, the real solar wind parameters around a near-earth orbit are used. The direction and strength of IMF are set to +Y direction which is perpendicular to the solar wind flow (+X direction) and 3 nT. Expressed in r_L/L (the ratio of an ion Larmor radius r_L of the solar wind at the magnetopause to a representative length of magnetic field L), when r_L/L = 0.1 (in the case of MHD scale), magnetopause is formed accompanied by a fast magnetosonic bow shock. When r_L/L = 2.0 (in the case of ion inertial scale), the electromagnetic interaction results in the formation of a magnetosphere with standing whistler waves. The drag coefficients, which is the thrust normalized by the solar wind inertial force, of both scales with IMF tend to increase compared with the cases without IMF because the incoming IMF accompanied by the solar wind piles up at upstream of the spacecraft. Also, on the ion inertial scale, the generation mechanism of Whistler wave and the influence of that on the thrust performance are revealed.

Signatures of the dissipation region of collisionless magnetic reconnection are investigated by the Geotail spacecraft for the 15 May 2003 event. The energy dissipation in the rest frame of the electron's bulk flow is considered in an approximate form D*(e), which is validated by a particle-in-cell simulation. The dissipation measure is directly evaluated from the plasma moments, the electric field, and the magnetic field. Using D*(e), a compact dissipation region is successfully detected in the vicinity of the possible X-point in Geotail data. The dissipation rate is 45 pWm(-3). The length of the dissipation region is estimated to 1-2d(i)(loc) (local ion inertial length). The Lorentz work W, the work rate by Lorentz force to plasmas, is also introduced. It is positive over the reconnection region and it has a peak around the pileup region away from the X-point. These new measures D*(e) and W provide useful information to understand the reconnection structure. Citation: Zenitani, S., I. Shinohara, and T. Nagai (2012), Evidence for the dissipation region in magnetotail reconnection, Geophys. Res. Lett., 39, L11102, doi:10.1029/2012GL051938.

A magnetic sail generates a propulsive force using the interaction between the solar wind and an artificial magnetosphere generated by a hoop coil. To investigate the electromagnetic thrust characteristics of the magnetic sail, such as the values of the drag, lift, transverse force, and pitching moment, three-dimensional hybrid (ion particle and electron fluid) particle-in-cell simulations are conducted in the range from the ion inertial scale to the magnetohydrodynamic scale. The drag values calculated in the different magnetic moment directions to the solar wind flow direction agree to within a factor of 2. The attitude of spacecraft is stable when the magnetic moment vector is perpendicular to the solar wind flow direction. It is found that these two results do not depend on the size of the magnetosphere.

Solar wind plasma behavior and thrust of a magnetic sail under the condition with interplanetary magnetic field (IMF) are examined by time-dependent, two-dimensional, X–Y  Cartesian, hybrid particle-in-cell (PIC) simulations. Magnetic sail is a propellant less propulsion system proposed for an interplanetary space flight. The thrust force is produced by the interaction between magnetic dipole field artificially generated by superconducting coils in a spacecraft and a solar wind. In the present simulations, the ratio of ion Larmor radius at the magnetopause to characteristic length of the magnetosphere is set to 0.1, and IMF strength is set to 0 and 10nT. As simulation results, magnetic reconnection occurs due to superposition of IMF and dipole field in the solar wind flow field. The reconnection points depend on the direction of IMF and those have an important role in the formation of shock wave. When IMF is perpendicular to the solar wind flow direction, the thrust acting on the spacecraft increases compared to the case without IMF. When IMF is parallel to the solar wind flow direction, lift force is generated on the spacecraft. These phenomena are attributed to the difference in location of magnetic reconnection point depending on the direction of IMF.

Solar wind interaction with a kinetic scale magnetosphere and the resulting momentum transfer process are investigated by 2.5-dimensional full kinetic particle-in-cell simulations. The spatial scale of the considered magnetosphere is less than or comparable to the ion inertial length and is relevant for magnetized asteroids or spacecraft with mini-magnetosphere plasma propulsion. Momentum transfer is evaluated by studying the Lorentz force between solar wind plasma and a hypothetical coil current density that creates the magnetosphere. In the zero interplanetary magnetic field (IMF) limit, solar wind interaction goes into a steady state with constant Lorentz force. The dominant Lorentz force acting on the coil current density is applied by the thin electron current layer at the wind-filled front of the magnetosphere. Dynamic pressure of the solar wind balances the magnetic pressure in this region via electrostatic deceleration of ions. The resulting Lorentz force is characterized as a function of the scale of magnetosphere normalized by the electron gyration radius, which determines the local structure of the current layer. For the finite northward IMF case, solar wind electrons flow into the magnetosphere through the reconnecting region. The inner electrons enhance the ion deceleration, and this results in temporal increment of the Lorentz force. It is concluded that the momentum transfer of solar wind plasma could take place actively with variety of kinetic plasma phenomena, even in a magnetosphere with a small scale of less than the ion inertial length. (C) 2012 American Institute of Physics. [doi: 10.1063/1.3683560]

Some numerical wear tests are conducted for the carbon/carbon ion optics of a microwave ion thruster μ10 engineering model to evaluate the accuracy and precision of JAXA's ion optics code (JIEDI). Through comparisons with experiment, the JIEDI code showed good agreement with a real-time 18,000-hrs life test when incorporating the motion of eroded grid materials and a low-energy sputtering yield model for the energy below 300 V. Numerical error caused by the uncertainty of physical model is also studied and it is found that uncertainty in beam current and plasma parameters cause 10% or less error to estimate grid hole erosion profiles. The grid erosion profile is most sensitive to the uncertainty in sticking factor, which indicates what percentage of eroded grid material arriving at a grid surface will re-deposit onto the grid surface. © 2011 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

The high-specification computational power of Japan Aerospace Exploration Agency's new supercomputer system, called Fujitsu FX1 cluster, enables us to perform really macroscale 3-D situations with full particle plasma simulation [particle-in-cell (PIC) method]. A fully 3-D kinetic approach to collisionless shock problems, which is one of the most important problems in the space plasma science, is possible, and a challenging run is being executed for a pioneering study of the topic. About 0.4 billion grids are allocated for the electromagnetic fields, and about 0.1 trillion particles are loaded into the simulation run. The computational efficiency of the PIC code is about 8% of the peak performance (4.6 Tflops) using 5776 CPU cores (57 Tflops). The simulation parameters were selected to simulate ESA's Cluster-II spacecraft observational result reported by Seki et al. (in 2009). The full mass ratio m(i)/m(epsilon) = 1840 was taken for this simulation, and almost one ion inertia length square could be allocated for the simulation. In this simulation, a quite complicated wave activity is found in the shock foot region. In this paper, comparing 3-D results with 2-D simulation results, a 3-D nature of shock transition region of quasi-perpendicular shock is reported.

We have performed 2.5-dimensional full particle simulations of an MHD-scale Kelvin-Helmholtz (KH) vortex and accompanying magnetic reconnection. This is the first study of so-called vortex-induced reconnection (VIR) using kinetic simulations. First, as a key property of the VIR, we found that magnetic reconnection occurs at multiple points in the current sheet compressed by the flow of the KH vortex. The resulting multiple mesoscale islands are carried toward the vortex body along the vortex flow and then are incorporated into the vortex body via re-reconnection. The rates of the first reconnection and second re-reconnection are both generally higher than that of spontaneous reconnection; both reconnection processes are of driven nature. Noteworthy is that the high rate of the first reconnection leads to strong magnetic field pileup within the multiple islands. This characteristic magnetic structure of the islands could be used as new observational evidence for the occurrence of the VIR. Next, as a key kinetic aspect of the VIR, we found that a series of the multiple island formation and incorporation processes causes efficient plasma mixing in real space and bidirectional magnetic field-aligned acceleration of electrons simultaneously within the vortex. These kinetic effects of the VIR could account for observed features of the Earth's low-latitude boundary layer, where mixed ions and bidirectional field-aligned electrons generally coexist.

The system size dependence of electron acceleration during large-scale magnetic island coalescence is studied via a two-dimensional particle-in-cell simulation. Using a simulation box that is larger than those used in previous studies, injection by merging line acceleration and subsequent reacceleration inside a merged island are found to be the mechanisms for producing the most energetic electrons. This finding and knowledge of the reacceleration process enable us to predict that the high energy end of the electron energy spectrum continues to expand as the merged island size increases. Both the merging line acceleration and the reacceleration within a merged island require the island coalescence process to be so dynamic as to involve fast in-flow toward the center of a merged island. Once this condition is met in an early stage of the coalescence, it is likely to stay in the subsequent phase. In other words, if the thin elongated current sheet is initially able to host the dynamic magnetic island coalescence process, it will be a site where repeated upgrades in the maximum energy of electrons occur in a systematic manner. (C) 2011 American Institute of Physics. [doi:10.1063/1.3554660]

Activity on numerical plasma simulations by JAXA’s Engineering Digital Innovation (JEDI) Center is overviewed. Currently, R&D of two major numerical tools is conducted. First one is spacecraft charging analysis tool that can compute charging status of a spacecraft solving charged particle motions precisely. Using this information, we can evaluate onboard measurement of electrostatic probes or consider better configuration of onboard equipment of a spacecraft. Computation example of the interactions between solar wind plasma and a solar sail is shown in this paper. Second one is a numerical tool called JIEDI (JAXA’s Ion Engine Development Initiative), which aims to reduce the cost and the time required for an ion thruster life test. The JIEDI tool can numerically estimate ion bombardment to an ion thruster’s grid material to predict the erosion rate of the grid material, and preliminary analysis by the JIEDI tool showed good agreement with the real-time life test of a microwave ion thruster.

The Geotail spacecraft made in situ observations of magnetic reconnection on 15 May 2003 in the near-Earth magnetotail at a radial distance of 28 R E when a moderate substorm started on the ground. For this event, the intense cross-tail electron current layer was detected in association with the simultaneous plasma flow and magnetic field reversals, and the scale length along the GSM x axis was obtained. This observation enables us to deduce scales for the basic structure of magnetic reconnection in the near-Earth magnetotail. In the center of the electron current layer (a possible X line), the speed of the dawnward electron flow carrying cross-tail current exceeds the maximum of the electron outflow speed (earthward/tailward), and it is highly super Alfvénic. The full extent of this central intense cross-tail electron current layer is approximately 1 λi (ion inertial length) in the x direction, which corresponds to 0.2 RE in the magnetotail. Electron outflow speed reaches its maximum, which is also super Alfvénic, at distances of less than 1 λi from the X line, and ion outflow speed reaches its maximum farther away from the center. Electron outflow speed decreases in the downstream region, and it becomes the same as the ion speed at distances of 4 λi. The full extent of the ion-electron decoupling region is 8 λi in the x direction, which corresponds to 1.5 RE in the magnetotail, and the outer region belongs to the MHD regime. Inside the ion-electron decoupling region, ions are accelerated up to 10 keV during inflow processes and further accelerated beyond 40 keV toward the duskward direction near the center and along the x axis slightly away from the center. These observations of the ion and electron dynamics in the close vicinity of the X line are fairly consistent with results from the two-dimensional particle-in-cell simulation described here and others. The present Geotail results provide the observational basis for the structure of magnetic reconnection in the near-Earth magnetotail. Copyright 2011 by the American Geophysical Union.

For the qualification of an ion thruster system for spacecraft, a time-consuming endurance test of more than 10,000 hours is required. To drastically reduce the cost and the time required for an ion thruster life test, a numerical tool called JIEDI (JAXA's Ion Engine Development Initiative) is under development. The JIEDI code numerically estimates ion bombardment to an ion thruster's grid material to predict the erosion rate of the grid material. Preliminary erosion rate analysis by the JIEDI code showed good agreement of erosion rate with a life test; the calculated grid erosion rate agrees with that of a life test within an accuracy of 40%. © 2011 by National Committee for IUTAM.

The "Conjunction Event Finder (CEF)" is a Web tool for seamlessly browsing quick-look (QL) data from many different kinds of satellites and ground-based instruments in solar-terrestrial physics. The QL plots are generally scattered all over the world, so that browsing many of them is so far very troublesome and inefficient. Just a simple procedure on the CEF, however, generates a collection of links to the QL plots for a period of interest, allowing us to check the data much more efficiently than ever. Hence this tool is powerful in finding interesting events of conjunction observations by satellites and ground-based instruments. The CEF is available in the Data ARchives and Transmission System (DARTS) at Institute of Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency (JAXA) in Japan.

In a thin elongated current sheet, it is likely that more than one X-line forms and thus multiple magnetic islands are produced. The islands are then subject to merging. By simulating such a case with a two-dimensional full-particle code, we show that a merger forming a large island produces the most energetic electron population in the system. By setting the lateral extent of the simulation box to be as large as similar to 100 ion inertial lengths, we introduce many (16) small islands in the initial thin current sheet (similar to 1 ion inertial length thickness). Merging of these islands proceeds to leave only two islands in the system. Then, strong electron acceleration is seen upon the final merger that produces the single island in the large simulation box. The most energetic electrons in the system are accelerated at the merging line. The merging line acceleration dominates because the reverse-reconnection facilitating the final merger is in such a strongly driven manner that the associated electric field is an order of magnitude larger than those available upon normal reconnection. Combining the results from additional runs enables us to obtain a scaling law, which suggests a non-negligible role played by merging lines in the observed electron acceleration phenomena. (C) 2010 American Institute of Physics. [doi:10.1063/1.3491123]

MAP-PACE (MAgnetic field and Plasma experiment-Plasma energy Angle and Composition Experiment) on SELENE (Kaguya) has completed its similar to 1.5-year observation of low-energy charged particles around the Moon. MAP-PACE consists of 4 sensors: ESA (Electron Spectrum Analyzer)-S1, ESA-S2, IMA (Ion Mass Analyzer), and IEA (Ion Energy Analyzer). ESA-S1 and S2 measured the distribution function of low-energy electrons in the energy range 6 eV-9 keV and 9 eV-16 keV, respectively. IMA and IEA measured the distribution function of low-energy ions in the energy ranges 7 eV/q-28 keV/q and 7 eV/q-29 keV/q. All the sensors performed quite well as expected from the laboratory experiment carried out before launch. Since each sensor has a hemispherical field of view, two electron sensors and two ion sensors installed on the spacecraft panels opposite each other could cover the full 3-dimensional phase space of low-energy electrons and ions. One of the ion sensors IMA is an energy mass spectrometer. IMA measured mass-specific ion energy spectra that have never before been obtained at a 100 km altitude polar orbit around the Moon. The newly observed data show characteristic ion populations around the Moon. Besides the solar wind, MAP-PACE-IMA found four clearly distinguishable ion populations on the day-side of the Moon: (1) Solar wind protons backscattered at the lunar surface, (2) Solar wind protons reflected by magnetic anomalies on the lunar surface, (3) Reflected/backscattered protons picked-up by the solar wind, and (4) Ions originating from the lunar surface/lunar exosphere.

Recent advancement in numerical techniques for Vlasov simulations and their application to cross-scale coupling in the plasma universe are discussed. Magnetohydrodynamic (MHD) simulations are now widely used for numerical modeling of global and macroscopic phenomena. In the framework of the MHD approximation, however, diffusion coefficients such as resistivity and adiabatic index are given from empirical models. Thus there are recent attempts to understand first-principle kinetic processes in macroscopic phenomena, such as magnetic reconnection and the Kelvin-Helmholtz (KH) instability via full kinetic particle-in-cell and Vlasov codes. In the present study, a benchmark test for a new four-dimensional full electromagnetic Vlasov code is performed. First, the computational speed of the Vlasov code is measured and a linear performance scaling is obtained on a massively parallel supercomputer with more than 12 000 cores. Second, a first-principle Vlasov simulation of the KH instability is performed in order to evaluate current status of numerical techniques for Vlasov simulations. The KH instability is usually adopted as a benchmark test problem for guiding-center Vlasov codes, in which a cyclotron motion of charged particles is neglected. There is not any full electromagnetic Vlasov simulation of the KH instability; this is because it is difficult to follow (E) over right arrow x (B) over right arrow drift motion accurately without approximations. The present first-principle Vlasov simulation has successfully represented the formation of KH vortices and its secondary instability. These results suggest that Vlasov code simulations would be a powerful approach for studies of cross-scale coupling on future Peta-scale supercomputers. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3422547]

Ion-to-magnetohydrodynamic scale physics of the transverse velocity shear layer and associated Kelvin-Helmholtz instability (KHI) in a homogeneous, collisionless plasma are investigated by means of full particle simulations. The shear layer is broadened to reach a kinetic equilibrium when its initial thickness is close to the gyrodiameter of ions crossing the layer, namely, of ion-kinetic scale. The broadened thickness is larger in B center dot < 0 case than in B center dot>0 case, where is the vorticity at the layer. This is because the convective electric field, which points out of (into) the layer for B center dot < 0 (B center dot>0), extends (reduces) the gyrodiameters. Since the kinetic equilibrium is established before the KHI onset, the KHI growth rate depends on the broadened thickness. In the saturation phase of the KHI, the ion vortex flow is strengthened (weakened) for B center dot < 0 (B center dot>0), due to ion centrifugal drift along the rotational plasma flow. In ion inertial scale vortices, this drift effect is crucial in altering the ion vortex size. These results indicate that the KHI at Mercury-like ion-scale magnetospheric boundaries could show clear dawn-dusk asymmetries in both its linear and nonlinear growth.

We have studied plasma (ion) pressure changes that occurred in association with the dipolarization in the near-Earth plasma sheet around substorm onsets. Using Geotail data, we have performed a superposed epoch analysis in addition to detailed examinations of two individual cases with special emphasis on the contribution of high-energy particles to the plasma pressure. It is found that, unlike previously reported results, the plasma pressure does increase in association with the initial dipolarization at X &gt ∼-12 RE and -2 &lt Y &lt 6 RE, with the increase largely due to high-energy particles. Outside the initial dipolarization region, particularly tailward and duskward of this region, the plasma pressure begins to decrease owing to the magnetic reconnection before onset or before the dipolarization region reaches there. At later times, the plasma pressure tends to increase there, related to the expanding dipolarization region, but the contribution of high-energy particles is not very large. These observations suggest the following. The rarefaction wave scenario proposed in the current disruption model is questionable. The radial and azimuthal pressure gradients may strengthen between the initial dipolarization and outside regions, possibly resulting in stronger braking of fast earthward flows and changes in field-aligned currents. The characteristics of the dipolarization may differ between the initial dipolarization and tailward regions, which would be possibly reflected in the auroral features. Furthermore, we have examined the specific entropy and the ion β. The specific entropy increases in the plasma sheet in the dipolarization region as well as in the midtail region in conjunction with substorm onsets, suggesting from the ideal MHD point of view that the substorm processes are nonadiabatic. The ion β is found to peak at the magnetic equator in the initial dipolarization region around dipolarization onsets. Copyright 2010 by the American Geophysical Union.

We had numerically analyzed charged particle effects on a solar sail in terms of charging in the interplanetary plasma environment at 0.5 AU, 1.0 AU, and 3.0 AU. The analyses were made focusing on the spatial distribution of the charged particles around the sail: the solar wind plasma and photoelectrons. Those can provide a guideline for the solar sail design, especially for onboard electrical instruments. A 3-D Electrostatic, full-Particle-In-Cell code was used to study precise charged particle behaviours, and MUSCAT, a spacecraft charging analysis tool, is additionally used to obtain differential voltage of a sail. The numerical results showed that a wake potential formed due to a large ion wake in the downstream region obstructed the diffusion of the photoelectrons to the rear surface of the sail. The size of the photoelectron cloud around a sail was estimated to be 17.5 m in the upstream hemisphere at 1.0 AU. The floating potential of the sail was +8.3 V at 1.0 AU, where double Maxwellian photoelectron spectrum model was adopted in the computation. The reduction of the electron sheath due to the photoelectron cloud was recognized, and that resulted in decrease of the ambient electron current onto the sail. The differential voltage on the rear insulator surface of the sail of -15.8 V was obtained by a MUSCAT computation, that showed the charging of a solar sail itself was not serious in this environment but would affect the photoelectron diffusion and the wake potential. These analyses were also made in the 0.5 and 3.0 AU plasma environment, and the results were discussed based on the computation results in the 1.0 AU plasma environment. Copyright ©2010 by the International Astronautical Federation. All rights reserved.

Magnetic sail is a propellantless propulsion system proposed for an interplanetary space flight. The propulsive force is produced by the interaction between the magnetic field artificially generated by a hoop coil equipped with the magnetic sail and the solar wind. Three-dimensional hybrid particle-in-cell simulations are performed to elucidate the plasma flow structure around the magnetic sail and to measure the propulsive force of the magnetic sail. We report the characteristics of the magnetosphere, such as the profile of the magnetic field, the thickness of the magnetopause current layer, and the predicted thrust value obtained by simulations, which agree well with laboratory experiment when simulations are carried out by considering the ion-neutral collision effect. The hybrid particle-in-cell simulation carried out without considering the collisional effect gave a thrust value of 3.5 N, which can be applied to the thrust evaluation of the magnetic sail in a magnetosphere with size of 300 kin in a collisionless interplanetary space.

The SmartSat Program is a collaborative program of government agency (NICT,JAXA) and private sector (MHI) in Japan to develop small satellite about 200 Kg. The space weather experiment of the SmartSat consists of Wide Field CME Imager (WCI), Space Environment Data Acquisition Equipment (SEDA), and mission processor (MP). Both of the instruments will be principal components of the L5 mission. WCI is a imager to track CME as far as earth orbit. CME brightness near earth orbit is expected 1E‐15 solar brightness or 1/200 of zodiacal light brightness. To observe such a extreme faint target, we are developing wide field of view camera with very high sensitivity and large dynamic range. These highly challenging experiment and demonstration will be implemented in SmartSat program.

A full particle-in-cell (PIC) plasma simulator with higher accuracy as well as reasonable performance for studying spacecraft-plasma interactions has been developed. It is applied to estimate characteristics of the onboard current monitors (CRM) for a small scientific satellite REIMEI in the polar orbit, because calibration is required for the observation data. Basic characteristics in typical plasma environments including effects of the satellite geometry are demonstrated.

A three-dimensional electrostatic full Particle-In-Cell code has been developed to analyze spacecraft-plasma interactions quantitatively. The code is expected to achieve highly accurate computation because it has no robust algorithm. We adopted the code to evaluate the electric field measurement onboard spacecraft, especially under low-density ambient plasma environment with photoelectron emission. In this paper, first, fundamental functions for computation of the electric field were validated in Low Earth Orbit and Geosynchronous Orbit environments by comparing with the thin-sheath limit theory and the thick-sheath limit theory, respectively. Second, the floating potential of a spacecraft model with photoelectron emission in Geosynchronous Orbit was computed to examine the effects of photoelectron emission to the electric potential around the spacecraft. The dependence of the floating potential on the photoelectron temperature was shown in the simulation.

In order to reach the new horizon of the space physics research, the Plasma Universe, via in-situ measurements in the Earth's magnetosphere, SCOPE will perform formation flying observations combined with high-time resolution electron measurements. The simultaneous multi-scale observations by SCOPE of various plasma dynamical phenomena will enable data-based study of the key space plasma processes from the cross-scale coupling point of view. Key physical processes to be studied are magnetic reconnection under various boundary conditions, shocks in space plasma, collisionless plasma mixing at the boundaries, and physics of current sheets embedded in complex magnetic geometries. The SCOPE formation is made up of 5 spacecraft and is put into the equatorial orbit with the apogee at 30Re (Re: earth radius). One of the spacecraft is a large mother ship which is equipped with a full suite of particle detectors including ultra-high time resolution electron detector. Among other 4 small spacecraft, one remains near (̃10km) the mother ship and the spacecraft-pair will focus on the electron-scale physics. Others at the distance of 100̃3000km (electron ̃ ion spatial scales) from the mother ship will monitor plasma dynamics surrounding the mother-daughter pair. There is lively on-going discussion on Japan-Europe international collaboration (ESA's Cross-Scale), which would certainly make better the coverage over the scales of interest and thus make the success of the mission, i.e., clarifying the multi-scale nature of the Plasma Universe, to be attained at an even higher level. © 2009 American Institute of Physics.

We had computed the spacecraft-plasma interactions in the magnetospheric plasma environment using a three-dimensional electrostatic full Particle-In-Cell code. In tenuous plasma environment, supersonic ions interacting positively charged spacecraft forms large-scale wake region in case the mean kinetic energy of ions is lower than the spacecraft potential. The scale length of a wake is almost comparable to the wire boom of a probe. Considering the potential structure formed by an ion wake, we had evaluated the electric field measurement observed by the Cluster spacecraft in the plasma trough environment. Evaluation of the wake formation in the polar wind environment is performed by comparing other numerical simulation. Evaluation for fundamental functions of the code is also described. Copyright © 2009 by the American Institute of Aeronautics and Astronautics, Inc.

We have newly developed an electron energy analyzer FESA (Fast Electron energy Spectrum Analyzer) for a future magnetospheric satellite mission SCOPE. The SCOPE mission is designed in order that observational studies from the cross-scale coupling viewpoint are enabled. One of the key observations necessary for the SCOPE mission is high-time resolution electron measurement. Eight FESAs on a spinning spacecraft are capable of measuring three dimensional electron distribution function with time resolution of 8 msec. FESA consists of two electrostatic analyzers that are composed of three nested hemispherical deflectors. Single FESA functions as four top-hat type electrostatic analyzers that can measure electrons with four different energies simultaneously. By measuring the characteristics of the test model FESA, we proved the validity of the design concept of FESA. Based on the measured characteristics, we designed FESA optimized for the SCOPE mission. This optimized analyzer has good enough performance to measure three dimensional electron distribution functions around the magnetic reconnection region in the Earth's magnetotail.

The steady state of dipolar magnetic field expansion is examined by injecting a plasma jet from the center of the dipolar magnetic field (magnetic inflation). An effective magnetic inflation is essential for the realization of a magneto plasma sail (MPS), which produces a propulsive force by the interaction between the solar wind and an artificial dipolar magnetic field that is inflated by the plasma jet injected from the spacecraft. During the process of magnetic inflation, the finite Larmor radius effect is of practical significance since rL/LB is considerably greater than unity in a region far from the center of the dipolar magnetic field. The simulation result obtained using the ideal magnetohydrodynamics (MHD) model is overestimated, namely, it shows that the inflated magnetic field decays according to |B| ∝ r -2.0 since the magnetic field is frozen into the plasma jet. In comparison with the MHD result, the results obtained using the hybrid particle-in-cell code are more accurate. These results show that the inflated magnetic field decays according to |B| ∝ r -2.3 under the condition βin = 1 since the finite ion Larmor radius effect decreases the flow of magnetic flux with respect to the flow of plasma jet.

We have studied the response of large-scale ionospheric convection to substorm expansion onsets on the basis of two weak substorms of 1 May 2001, during which a large part of the dawn cell of the two-cell ionospheric convection pattern was monitored by the SuperDARN radars. Ionospheric convection began to enhance first in a localized region of the equatorward part of the dawn cell ∼2 minutes before the expansion onsets of both substorms and then enhanced in the entire dawn cell successively. The enhanced convection persisted throughout their expansion phase, possibly even near the footprint of a plasma sheet region without fast flows observed by Geotail. These observations suggest that ionospheric convection begins to enhance just before substorm expansion onset and then enhances in the entire cell, possibly regardless of the presence of fast earthward flows in the corresponding plasma sheet region of the magnetotail. The global enhancement of ionospheric convection is consistent with that of magnetotail convection, which also begins just before onset.