PEM26-01

Room:302

Time:May 24 09:00-09:15

Magnetic reconnection in viscosity-dominated plasmas
MINOSHIMA, Takashi1∗ ; IMADA, Shinsuke2 ; MIYOSHI, Takahiro3
1

Japan Agency for Marine-Earth Science and Technology, 2 Solar-Terretrial Environment Laboratory, Nagoya University, 3 Departmentof Physical Science, Graduate School of Science, Hiroshima University
Magnetic reconnection is essentially multi-scale phenomenon. From fully kinetic to magnetohydrodynamic (MHD) scales, awide variety of models are utilized to identify triggering mechanisms for fast reconnection. The so-called GEM reconnection
challenge has compared numerical simulations with fully kinetic (Particle-In-Cell), partly kinetic (Hybrid and Hall-MHD), andconventional resistive MHD models under the same initial condition, and it has shown that only the MHD model cannot achieve
fast reconnection (Birn et al. 2001). This result indicates that kinetic effects are the essential physics and the resistive MHD isinsufficient to model fast reconnection.
There are several kinetic effects proposed for the candidate to trigger fast reconnection, such as the Hall effect, the dispersionof whistler waves, the electron inertia and pressure anisotropy. We particularly focus on a two-scale structure in the diffusion
region. In the fully kinetic model of electron-ion plasmas, the diffusion region is composed of a thinner electron diffusion region
embedded in a thicker ion diffusion region. We hypothesize that fast reconnection may be triggered even in the MHD model if it
attains a two-scale diffusion region like the kinetic model. Since the ion and electron diffusion regions are respectively measured
as the vortex and current sheet, the two-scale diffusion region may be observed in the visco-resistive MHD with the viscosity
larger than the resistivity (i.e., magnetic Prandtl number is larger than unity). However, this is not expected in conventional MHD
simulations because they often use only the resistivity and ignores the viscosity (i.e., magnetic Prandtl number is almost zero).
Then, we perform two-dimensional visco-resistive MHD simulations of magnetic reconnection in viscosity-dominated plasmas. A simple Harris sheet configuration with uniform viscosity and resistivity is assumed as an initial configuration. When theviscosity is sufficiently high, the two-scale structure of thicker vortex and thinner current sheet is observed in the diffusion region,and subsequently, the diffusion region begins to thin down. The thinning speed increases with decreasing the thickness, implyingthat the thinning is driven by the viscous vortex motion. The vortex originates from the viscous heating at the downstream. Highviscosity immediately dissipates and opens the outflow jet, thus tends to localize the diffusion region. We observe the upstream
propagation of rarefaction waves, which accelerate the plasma toward the diffusion region. As a result, the current sheet in thevisco-resistive MHD model becomes much thinner than in the resistive MHD model. Explosive reconnection is expected in thevisco-resistive MHD. Since the magnetic Prandtl number is estimated to be much larger than unity in hot and tenuous astrophysical plasmas (e.g., stellar corona and active galactic nuclei disks), our result indicates the importance of the visco-resistive MHD
against the conventional resistive model.
Keywords: magnetohydrodynamics (MHD), magnetic reconnection

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PEM26-02

Room:302

Time:May 24 09:15-09:30

Numerical simulation of asymmetric reconnecton with GPUTAISUKE, Fuchida1∗
1

Graduate School of Science and Engineering

Magnetic reconnection is generally accepted as an important elementary process in the geo-magnetosphere. Especially, theasymmetric reconnection is more general than the symmetric one. So it takes an important role on clarifying Anemone type flaresand flux transfer events at the dayside magnetopause, and so on. However, it is also a phenomenon that have many unsolved
problems. We aim to understand the asymmetric magnetic reconnection by numerical simulation based on MHD equations.
In this calculation, GPU-accelerated computing(GPGPU) was performed. Although we use only one GPU now, we are going to
use multiple GPUs. In that case, the slow transmission speed between CPU and GPU becomes a large problem. On the parallel
computing with multiple GPUs, calculation domain is divided into arbitrary pieces and each GPU must have the information
required to calculate in a each device memory. However, the transferring of the data between GPU-GPU is not permitted. Insteadof it, we use the communication between CPU-GPU. This process becomes the bottle neck and this GPU-accelerated computing
is not effective. In order to avoid this problem, we hide the data communication between CPU-GPU behind the GPU calculation.
Furthermore, using this GPGPU code we confirmed the previous study by Cassak & Shay in 2007 that in the asymmetricreconnection, X-point moves toward the weak magnetic field side.
Keywords: asymmetric reconnection, GPGPU, parallel calculation

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PEM26-03

Room:302

Time:May 24 09:30-09:45

An MHD-scale dynamics of collisionless magnetic reconnection
FUJIMOTO, Keizo1∗ ; TAKAMOTO, Makoto2
1

Division of Theoretical Astronomy, NAOJ, 2 Max-Planck-Institute for Nuclear Physics

We usually believe that an MHD-scale dynamics can be adequately described with the MHD approximation. However, thisidea is not always straightforward in collisionless plasmas, where the time scale of thermal relaxation is much larger than that ofphenomena of interest. The present study considers this problem for magnetic reconnection.
Magnetic reconnection is an explosive energy converter from the magnetic field energy into plasma kinetic energy. The
reconnection processes are believed to play a key role in energetic phenomena in space such as geomagnetic substorms, solar
flares, and the generation of the pulser wind. One of the main issues in reconnection has been the mechanism that enables fast
energy release in a realistic time scale. Since the reconnection processes give rise to a MHD-scale dynamics, a lot of reconnection
models have been developed historically in the MHD framework. One of the most promising models is the Petschek model
suggested in 1964. The Petschek model provides a fast reconnection in a wide range of plasma conditions (leading to magnetic
Reynolds number). The key assumptions of the model are a compact diffusion region localized in the vicinity of the x-line and apair of the switch-off slow shocks extending from the x-line. The compact diffusion region is necessary to keep the reconnection
rate high, avoiding the current sheet from elongation. Most part of the plasma is accelerated at the slow shocks, which allow
the energy conversion in a broad area downstream the x-line. Although the Petschek model has been demonstrated by the MHD
simulations under certain setups, the model has not been accepted. In fact, the dynamical behavior of reconnection depends
significantly on the resistivity model in the MHD simulations, and clear slow mode shocks have merely been observed in geomagnetosphere.
To assess the MHD reconnection model, the present study has performed huge-scale particle-in-cell (PIC) simulations withthe help of the adaptive mesh refinement (AMR). The simulation domain extends to more than 600 ion inertia length in theoutflow direction with a large ion-to-electron mass ratio and an open boundary condition. We believe that the system size issufficiently large to describe the MHD-scale dynamics of reconnection. After a long-time evolution, we find that a long current
layer is formed in the exhaust, which is reminiscent of the Sweet-Parker reconnection model. However, the magnetic dissipation
takes place only around the x-line, so that the reconnection rate remains high as in the Petschek model. The transient region
formed around the field line separatrix almost satisfies the Rankine-Hugoniot relation for the slow mode shock. However, wefound that no plasma acceleration occurs in the transient region. Instead, the ions are accelerated in the current layer through the
Speiser motions, while the electrons gain the energy in the Hall region from the reconnection electric field. Therefore, the plasma
acceleration mechanism in collisioneless reconnection is different clearly from that in the Petschek model. The decouplingmotions between the ions and the electrons generate the Hall current even far downstream the x-line. Thus, the dynamics inthe exhaust is not able to be described in the MHD framework. The present study suggests that magnetic reconnection is an
MHD-scale phenomenon, but the MHD approximation is not adequate in collisionless plasmas.

Keywords: magnetic reconnection, particle-in-cell simulation, MHD-scale dynamics, plasma acceleration

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PEM26-04

Room:302

Time:May 24 09:45-10:00

Study of fast magnetic reconnection by using newly high resolution MHD scheme
OGAWA, Masanori1∗
1

Department of Earth and Planetary Science, The University of Tokyo

Magnetic reconnection is an important process to drive explosive release of magnetic energy by reconnecting anti-parallel
magnetic lines in space plasma, such as particle acceleration in solar flares and large-scale convection in the Earth’s magnetosphere. Magnetohydrodynamics (MHD) simulation where plasmas are treated as fluid is one of the useful methods to learn
macroscopic effects of magnetic reconnection. However, kinetic effects of plasma particles around an X-line are significant todrive fast reconnection, since the MHD approximation is broken in the vicinity of the X-line. Consequently, reconnection rate
which means energy release efficiency is low ,the so called slow reconnection. Previous researches have shown that particle
simulations including kinetic effects achieve fast reconnection, while MHD simulations do not[e.g., J. Birn et al., 2001].
In this study,we attempt to simulate the fast magnetic reconnection by using a newly high order MHD scheme proposed by S.
Kawai[2013]. The results show reconnection rate is higher than previous results by MHD simulations.In addition, we confirm
the dependence on spatial resolution of reconnection rate. As the resolution is higher, the reconnection rate is expected to behigher, since current sheet becomes thinner. As a result, global reconnection rate increases in proportion to the resolution. Notethat simulations with high resolution allow secondary magnetic islands. That is, the increase of global reconnection rate is dueto the multiple X-lines. We confirm, however, local reconnection rate at one of the X-lines, and the rate is equivalent to thatfrom previous particle simulations. Consequently, these results show that the newly scheme enables us to perform fast magnetic
reconnection and is useful to study magnetic reconnection in the MHD-scale phenomenon.
Keywords: magnetic reconnection, magnetohydrodynamics

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PEM26-05

Room:302

Time:May 24 10:00-10:15

Dynamical Petschek Reconnection: New Mechanism of Fast Magnetic Reconnection
SHIBAYAMA, Takuya1∗ ; KUSANO, Kanya1 ; MIYOSHI, Takahiro2 ; NAKABOU, Takashi1 ; VEKSTEIN, Grigory3
1

Solar-Terrestrial Environment Laboratory, Nagoya University, 2 Hiroshima University, 3 University of Mancheter

Magnetic reconnection is a process to change the connectivity of magnetic field lines and thought to play a core role for
explosive energy conversion from magnetic energy to kinetic and thermal energies during solar flare, magnetospheric substorm,
and tokamak disruption. However, electric conductivity in the solar corona, where solar flares occur, is quite large. According
to the Sweet-Parker theory, it is difficult to conduct magnetic reconnection efficiently in such highly conductive field. Petschek
proposed another reconnection theory, in which small magnetic diffusion region realizes effective reconnection even in the solar
corona. Magnetic energy is converted to thermal and kinetic energy in slow mode MHD shocks. Recent numerical simulations,however, suggest that Petschek reconnection is not stable in a system of spatially uniform resistivity. Some mechanism such as
anomalous resistivity is needed to sustain the local diffusion region. It is, therefor, not elucidated yet that Petschek reconnection
occurs spontaneously.
We perform resistive MHD simulation in a large system with a high spatial resolution and find slow mode MHD shocks, which
are predicted by Petschek, spontaneously form even with the uniform resistivity. In this process, fast motion of large plasmoidsin the current sheet play an important role and slow mode shocks form in front of moving plasmodia (fig1). This process exceeds
magnetic reconnection intermittently and repeatedly because plasmoids are ejected and form repeatedly. This process enhances
reconnection and achieve normalized reconnection rate of 0.01, which is necessary to explain the time scale of solar flares (fig2).
We name this fast reconnection regime ’Dynamical Petschek Reconnection’. In this regime, microscopic physics or anomalous
resistivity is not necessary and only uniform resistivity is enough to realize fast reconnection. Motion of plasmoid affect thesurrounding plasma flow and this flow play a role to localize electric current. As a consequence, slow mode MHD shocks, which
are predicted by Petschek, form spontaneously and energy conversion occurs efficiently.
Keywords: Magnetic reconnection, Solar flare

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PEM26-06

Room:302

Time:May 24 10:15-10:30

Resistive magnetic reconnection in a plasma stream
MIYOSHI, Takahiro1∗ ; KUSANO, Kanya2 ; SHIBAYAMA, Takuya2
1

Graduate School of Science, Hiroshima University, 2 Solar-Terrestrial Environment Laboratory, Nagoya University

Magnetic reconnection is a fundamental process in plasma physics which plays an essential role for various space and astrophysical explosive phenomena. It is one of the most important issues in plasma physics to elucidate the physical mechanism of
fast magnetic reconnection in high Lundquist number plasmas. In recent years, using high-resolution MHD simulations, it has
been shown that a new fast magnetic reconnection process may be driven by a secondary instability in a thin current sheet involving a plasma stream (Sweet-Parker-type current sheet) [1]. Moreover, state-of-the-art very-high-resolution MHD simulation
indicated that Petschek-type magnetic reconnection may dynamically be triggered by a complicated interaction with the plasma
stream around the current sheet [2]. Therefore, we can expect that magnetic reconnection in the plasma stream becomes a key
process for fast magnetic reconnection in high Lundquist number plasmas.
Although several theoretical and numerical studies for the tearing instability in an anti-parallel magnetic field including afield-aligned plasma stream, i.e., the streaming tearing instability, have been reported so far [3], the nonlinear dynamics of welldeveloped magnetic reconnection in the plasma stream has not been clarified yet. Thus, the objective of this paper is to explore
the nonlinear dynamics of resistive magnetic reconnection in the plasma stream using the MHD simulation. In this study, nonlinear magnetic reconnection was triggered by a large perturbation in the Harris-type equilibrium with a localized field-aligned
plasma stream. The results indicated that the current sheet structure of the reconnection point is varied depending on the bulk
speed of the localized plasma stream. We found that the current sheet can be localized when the bulk speed is less than the Alfven
speed.
[1] N. F. Loureiro, et al., Phys. Plasmas, 19, 042303 (2012)[2] T. Shibayama, et al., in preparation[3] T. Sato, R.J. Walker, J. Geophys. Res., 87, 7453-7459 (1982)
Keywords: magnetic reconnection, plasma stream, MHD

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PEM26-07

Room:302

Time:May 24 10:30-10:45

Loading Relativistic Maxwell Distributions in Particle Simulations
ZENITANI, Seiji1∗
1

NAOJ

Numerical algorithms to load relativistic Maxwell distributions in particle-in-cell (PIC) and Monte-Carlo simulations arepresented. For stationary relativistic Maxwellian, the inverse transform method and the Sobol algorithm are reviewed. To boost
particles to obtain relativistic shifted-Maxwellian, two rejection methods are proposed in a physically transparent manner. Their
acceptance efficiencies are 50% or 100%, respectively. Our simple methods can be combined with arbitrary base algorithms andarbitrary distribution functions.
Keywords: PIC simulation, relativity, Monte-Carlo

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PEM26-08

Room:302

Time:May 24 11:00-11:15

Effects of EMIC rising tone emissions on energetic particles in the inner magnetosphere
SHOJI, Masafumi1∗ ; OMURA, Yoshiharu2
1

Solar-Terrestrial Environment Laboratory, 2 Research Institute for Sustainable Humanosphere

Rising tone electromagnetic ion cyclotron (EMIC) emissions, or so-called EMIC triggered emissions, have been observed in
the inner magnetosphere. In order to reproduce the EMIC triggered emissions, we perform self-consistent hybrid simulations
with a real scale non-uniform ambient magnetic field model. We obtained two different triggered emissions, coherent rising
tone emission and broadband EMIC bursts, which are generated in high and low magnetic field gradient model, respectively.
We estimate effects on plasmas by the EMIC rising tone emissions in the inner magnetosphere. For energetic protons, which
drive EMIC waves, broadband emissions induce rapid precipitation of energetic protons into the loss cone since the scatteringby the concurrent triggering takes place faster than that of the coherent emissions. On the other hand, the coherent triggeredemission causes efficient proton acceleration around the equator because of the stable particle trapping by the coherent rising
tone emission. The rising tone EMIC waves also causes an effective heating of cold heavy ions by parallel electric field inducedby counter-propagating EMIC waves. The generation of the EMIC waves are also modulated due to the cold ion heating.
Relativistic electron scattering by the rising tone emissions reproduced by the hybrid simulations are also estimated by test
particle simulations. Nonlinear trapping causes significant electron scattering in wide energy range. Broadband EMIC waves
induce rapid, weak and continuous precipitations.
Keywords: inner magnetosphere, hybrid simulation, wave-particle interaction

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PEM26-09

Room:302

Time:May 24 11:15-11:30

Dependencies of the generation process of whistler-mode emissions on temperature anisotropyof energetic electrons
KATOH, Yuto1∗ ; OMURA, Yoshiharu2 ; MIYAKE, Yohei3 ; USUI, Hideyuki3 ; NAKASHIMA, Hiroshi4
1Graduate School of Science, Tohoku University, 2 Research Institute for Sustainable Humanosphere, Kyoto University, 3 Graduate
School of System Informatics, Kobe University, 4 Academic Center for Computing and Media Studies, Kyoto University
By a series of electron hybrid simulations, we study dependencies of the generation process of whistler-mode chorus andhiss-like emissions on temperature anisotropy of energetic electrons.
Whistler-mode chorus emissions are electromagnetic plasma waves commonly observed in planetary magnetospheres. In the
Earth’s inner magnetosphere, chorus emissions are observed mostly on the dawn side and are enhanced during geomagnetically
disturbed periods. Chorus emissions appear in the typical frequency range from 0.2 to 0.8 fce0 with a gap at the half fce0 , where
fce0 represents the electron gyrofrequency at the magnetic equator. Recent in situ observation in the magnetosphere revealed thepresence of whistler-mode hiss-like emissions, whose wave amplitude is comparable to those of chorus emissions.
The generation process of chorus has been reproduced in electron hybrid simulations and has been explained by the nonlinear
wave growth theory [see review by Omura et al., in AGU Monograph ”Dynamics of the Earth’s Radiation Belts and Inner Magnetosphere, 2012]. The generation mechanism of hiss-like emissions is also explained by the nonlinear wave growth theory and has
been reproduced by simulations [Katoh and Omura, JGR 2013]. In the present study, by an improved electron hybrid code with
OhHelp library [Nakashima et al., 2009], we conduct a series of electron hybrid simulations for different temperature anisotropy(AT ) of the initial velocity distribution function of energetic electrons. We vary AT in the range from 3 to 9 with changing thenumber density of energetic electrons (Nh ) so as to study whether distinct rising-tone chorus emissions are reproduced or not in
the assumed initial condition. Based on the simulation results, we reveal properties of the chorus generation for the assumed AT
parameter range.
Keywords: whistler-mode chorus, the Earth’s inner magnetosphere, numerical experiments

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PEM26-10

Room:302

Time:May 24 11:30-11:45

A self-consistent model of helicon plasma production
ISAYAMA, Shogo1∗ ; HADA, Tohru1
1Interdisciplinary Graduate School of Engineering Sciences, Kyushu University

Helicon plasma is a high-density and low-temperature plasma generated by the electromagnetic (Helicon) wave excited in
the plasma. Then, helicon plasma is expected for various applications. On the other hand, there still remain a number of
unsolved physical issues regarding how the plasma is generated using the helicon wave. The mechanism of helicon plasma
production includes the wave propagation in the plasma (dispersion relation), collisional or non-collisional wave damping andplasma heating, and ionization/recombination of neutral particles which causes time evolution of the dispersion relation. In
this study, we use the linear theory of helicon plasma, fluid simulation, and particle simulation to construct self-consist model
including these physics.
In previous, we studied the helicon wave propagation and the process of plasma heating. And we showed the efficiency of mode
conversion in bulk plasma depends strongly on the magnitudes of dissipations. However, there is a problem that has not beenmuch studied: How do the helicon and TG modes influence the plasma density, electron temperature and their profiles? Whilethe helicon mode is absorbed in the bulk plasma, the TG mode is mostly absorbed near the edge of the plasma. The local power
deposition in a helicon plasma is mostly balanced by collision loss. This local power balance can give rise to an inhomogeneouselectron temperature profile which is related to time evolution of density profile. In our study, we construct a self-consistentdischarge model which includes wave excitation, classical electron heat transfer, and diffusion of charged particles.

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PEM26-11

Room:302

Time:May 24 11:45-12:00

A theoretical model of nonlinear Alfven waves including kinetic compressional modes
NARIYUKI, Yasuhiro1∗
1

Faculty of Human Development, University of Toyama

It is well known that magnetohydrodynamic (MHD) turbulence in solar wind plasmas often has clear correlations between
magnetic field and velocity field (Alfvenic correlations). Although it is widely believed that Alfvenic fluctuations play importantrole in making developed MHD turbulence and scattering charged particles, damping processes of the fluctuations have not beenclarified yet. Over the nearly four decades, nonlinear evolution equation of Alfven waves has been discussed by many authors.
Mio etal(1976) and Mjolhus(1976) derived a nonlinear evolution equation of envelope-modulated Alfven waves. Rogister(1971),
Mjolhus and Wyller(1988), and Spangler(1989,1990) derived a kinetic-fluid model including nonlinear Landau damping ofcompressional fluctuations. Hada (1993) derived a nonlinear evolution equation set including compressional propagating modeby using a novel expansion. In the present study, we discuss a nonlinear evolution equation of Alfven waves including bothkinetic effects and compressional modes. Such a model was phenomenologically discussed by Nariyuki and Hada(2007). We
here systematically derive and discuss the expansion of Hada (1993) in the resultant kinetic-fluid model. We also discuss effectsof mean fields and thermal noises.

Keywords: Alfven waves, kinetic theory, solar wind

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PEM26-12

Room:302

Time:May 24 12:00-12:15

A Pedagogical Calculation on the Poraziation Vector in an MHD Wave
NAKAMURA, Tadas1∗
1

Fukui Prefectural University

The concept of electric polarization has been examined using an MHD (magnetohydrodynamic) wave for educational purpose.
The polarization in an MHD wave can be easily derived from the basic equations, and its mechanism is transparent undergraduate
students.
The polarization vector may be one of the most unclear concept in electromagnetism for students. Standard explanation of P
is based on the molecular polarization of a dielectric medium, however, actual mechanism of the polarization is not consistently
treated in textbooks usually. One needs to examine the molecular dynamics of the medium, which requires to solve quantum
many-body problem somehow, to this end. A consistent quantum model is beyond the power of undergraduate students who arestarting electromagnetism.
In the present paper, a simple and selfconsistent example of the electric polarization is introduced: an magnetohydorodynamic(MHD) wave in a collisionless plasma. The molecular polarization is not the only mechanism to cause the polarization vector. It
can be the result of any current in the medium invoked by the electric field E, as long as E and P
are in linear relation.
When we examine the polarization in an MHD plasma closely, we find that the polarization vector P does not correspond toany actual physical entity. The response of the plasma as a dielectric media takes place in the form of the polarization current,
and P is a convenient mathematical expression to handle the effect of the polarization current. This situation is somewhat similar
to the relation of an electric potential to electric fields. What we actually observe is the electric fields, but calculations become
easier when we introduce a potential function.
Keywords: MHD wave, Polarization Vector, Electric field and Electric Flux

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PEM26-13

Room:302

Time:May 24 12:15-12:30

Modeling of Particle Acceleration in Shock-Shock Interaction
NAKANOTANI, Masaru1∗ ; MATSUKIYO, Shuichi1 ; HADA, Tohru1
1

IGSES,Kyushu University

It is known that collisionless shocks produce high energetic particles (cosmic rays). Most of the past studies have been
dedicated to discussing particle acceleration in a single shock system. Particle acceleration in multiple shocks, however, isconsidered to be highly efficient[Gieseler and Jones, 2000, Melrose and Pope, 1993]. In space, two shocks are frequently comeclose to and even collide with each other. For instance, it is observed that a coronal mass ejection(CME) driven shock collides
with the earth’s bow shock[Hietala et al., 2011,Concharov et al., 2014], or interplanetary shocks pass through the heliospherictermination shock[Lu et al., 1999].
To investigate the shock-shock interaction, we perform one-dimensional full particle-in-cell simulation in which two identicalshocks collide. We found that electrons are accelerated through multiple reflection between the two shocks(Fermi acceleration).
These electrons excite large amplitude waves between the two shocks and are scattered in their pitch angles. The scatteringresults in that some electrons can have sufficiently large pitch angles so that they are easily reflected when they reach at a shocknext time. We model the acceleration process and discuss the suitable condition for particle acceleration.

Keywords: Collisionless Shocks, Shock-Shock Interaction, Particle Acceleration

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PEM26-14

Room:302

Time:May 24 12:30-12:45

Detection of Group of Black hole Binaries at the Center Part of Our Galaxy Based on
OYA, Hiroshi1∗
1

Tohoku University

1. Introduction Through the current studies on the detection of Ker
Black holes located at the center part of our Galaxy, being based on the observations of decameter radio wave pulses, theinvestigation of the accurate source direction has been made for the largest case of Gaa and Gab. In this study, the works has
been expanded to other 3 cases such as , Gac-Gad, Gae-Gaf and Gag-Gah systems. The directions of sources of decameter wave
pulses are analyzed using newly observed data in 2014 considering the deviation effects, of the ionosphere, on the propagating
direction of radio wave.
2. Observation System The observations to determine the source direction of
the decameter radio wave pulses have been carried out using the long baseline decameter radio wave interferometer of Tohoku
university which consist of three observation stations located at Yoneyama, Kawatabi and Zao in Miyagi Prefecture, Japan; thelongest baseline is 84km and shortest baseline is 44km. The signals observed at 22.186MHz with band width of 1kHz are sentfrom each station through the telemetry system directly to the central station at Sendai where the detected signals are converted
into digital signals by AD converters with conversion rate of 6000 data per second being divided into 3 channels with 100Hz
band width.
3. Data Analyses Observations in 2014 have been made from earlyFebruary to 10th of April. In this work the data observed March 18, 19, and 20 are selected for analyses. The pulse form isdetected by applying period correlated accumulation method (so called box car method modified for varying periods) together
with analyses of correlation between interferometer fringe and template fringes to decide the source direction. To form thetemplate fringe the ionosphere effect for propagation of radio waves at 22.816MHz are considered by applying 3-layer-ionospheremodel where foF2 values observed at Kokubunji station are applied. A fine adjustment to compensate the systematic bias of thedetected source direction due to the characteristic of the selected ionosphere model, is made by searching the direction of thetemplate fringe.
4. Results and Discussions
4.1Source Direction Source directions are obtained in forms of correction
angles deviating from the predicted Sgr A∗direction that are calculated with consideration of ionosphere effects. The caseof Gaa-Gab binary, results are given as Gaa(RA(0.01,0.53);Dec(-0.45,0.63))–Gab(RA(0,109);Dec(-1.53,1.33)). This format
indicates that for Gaa average deviation angle for RA (right ascension) of Gaa is 0.01 arc minutes with standard deviation of
0.53 arc minutes and average correction angle for Dec(declination) of Gaa is -0.45 arc minutes with standard deviation of 1.33
arc minutes. Though detail values for other BH binary system will be given in the presentation, the results show that with only
one exception of the case of declination of Gab, all average correction angle are within the deviation angle, suggesting that thesource directions coincide with SgrA∗within an error of 1.89 arc minutes.
4.1 Parameters of BH binary Systems The sources of pulses are assumed
to be Ker black holes with masses which are approximately proportional to the pulse periods. Applying Kepler law using
orbital parameters resulted from observed periods , then masses of BH of binary system have been derived.
5. Conclusion Within determination error of 1.89 arc minutes, there exist
at least 4 binary systems in Sgr A∗such as Gaa-Gab, Gac-Gad, Gae-Gaf, and Gag-Gah system which show orbital periods,
respectively 2050 sec, 1024 sec, 1200sec and 325 sec. Each black hole has mass as given with unit of million solar mass from1.30 to 1.32, for Gaa; from 1.04 to 1.07, for Gab; from 0.82 to 0.84 for Gac; from 0.57 to 0.60, for Gad; from 0. 15 to 0.17,for
Gae ; from 0.11 to 0.14, for Gaf ; from 0.17 to 0.18, for Gag and from0.14 to 0.15 for Gah.

Keywords: Black Hole, Binary, Decameter Radiowave, Interferometer, Galaxy Center

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PEM26-15

Room:302

Time:May 24 14:15-14:30

Gas accretion and particle acceleration during collisionless magnetorotational instability
HOSHINO, Masahiro1∗
1

University of Tokyo

Enhanced angular momentum transport and efficient particle acceleration during the magnetorotational instability (MRI) in acollisionless accretion disk are studied using three-dimensional particle-in-cell (PIC) simulation with a pitch-angle isotropization
model. It is well known that the magnetic reconnection plays an important role on the nonlinear saturation of MRI, and we findthat the plasma pressure anisotropy inside the channel flow with pk >p⊥ induced by active magnetic reconnection during thenonlinear stage of MRI suppresses the onset of subsequent reconnection, which in turn leads to high magnetic field saturationand enhancement of Maxwell stress tensor of angular momentum transport. Meanwhile, during the quiescent stage of reconnection the plasma isotropization progresses in the channel flow, and the anisotropic plasma with p⊥ >pk due to the dynamo
action of MRI outside the channel flow contributes to rapid reconnection and strong particle acceleration. This efficient particle
acceleration and enhanced angular momentum transport in a collisionless accretion disk may explain the origin of high energy
particles observed around massive black holes.
Keywords: accretion disk, magnetorotational instability, angular momentum transport, particle acceleration, magnetic reconnection, turbulence

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PEM26-16

Room:302

Time:May 24 14:30-14:45

Instability and Turbulence Generation through Non-uniform Toroidal Magnetic Field in
Accretion DisksHIRABAYASHI, Kota1∗ ; HOSHINO, Masahiro1
1

Graduate School of Science, The University of Tokyo

Plentiful dynamics observed in accretion disks, e.g. disk winds, jets, and outflows, are believed as the results of angularmomentum transport highly enhanced by magnetohydrodynamic turbulence. The magneto-rotational instability (MRI) is oneof the most successful mechanisms to drive the required turbulent state, and generates a large toroidal magnetic field in the
nonlinear evolution. In this study, we investigate the local stability of accretion disks especially focusing on the stage when thetoroidal field is dominant, which is important to understand the dynamics and the nature of turbulence in well-developed disks,and suggest another possible path leading to the turbulent generation.
It is known that the differentially rotating plasmas threaded by the uniform toroidal field are unstable essentially for the
perturbation with a vertical wavevector. Our linear analysis, however, shows that if the initial toroidal field has non-uniformity,
the unstable modes confined within the equatorial plane, or with no vertical wavenumber, appear. Furthermore, a series of twodimensional nonlinear simulations reveal that when the plasma beta is not so low (roughly β>1), this unstable mode can growas far as the background field configuration breaks down. As another possible situation, we study the stability of the toroidal
field with wavy structure. The simulations show that after the above unstable modes grow enough to interact with neighboringmodes, they couple, marge, and eventually evolve to very turbulent state. In the saturated stage, the alpha parameter describing
the efficiency of the angular momentum transport reaches to the same level with the previous studies of a toroidal MRI. Thisinstability plays an important role in plasma transport since it may couple with magnetic reconnection occurring in an equatorial
plane and then contribute to the saturation mechanism of MRI.

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PEM26-17

Room:302

Time:May 24 14:45-15:00

Hybrid simulation of an ion scale magnetosphere: Structure of the magnetopause boundary
NAKAMURA, Masao1∗
1Osaka Prefecture University

An ion scale magnetosphere is studied by performing a three-dimensional hybrid simulation. The hybrid simulation treats
the ions as kinetic super particles via a particle-in-cell method and the electrons as a massless fluid. In this study, the ion scale
magnetosphere has a dayside stand-off distance which is several to a hundred times larger than the ion Larmor radius of the solar
wind proton in the magnetic field strength which magnetic pressure equals to the solar wind dynamic pressure. The daysidemagnetopause boundary has a double- or triple-layer flow structure due to the finite Larmor radius effect in the interaction between the solar wind and the magnetosphere. The flow structure is controlled by the interplanetary magnetic field. For the small
ion scale magnetosphere, the bow shock cannot well steepen because the dayside sheath thickness is an order of the ion Larmor
radius and the shock transition region overlaps with the boundary flow structure. We will discuss the plasma convections, current
flows, and field structures in various solar wind conditions.
Keywords: Ion scale magnetosphere, hybrid simulation

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PEM26-18

Room:302

Time:May 24 15:00-15:15

Numerical simulation of active spacecraft charging in interplanetary space
HOSHI, Kento1∗ ; MURANAKA, Takanobu2 ; KOJIMA, Hirotsugu3 ; YAMAKAWA, Hiroshi3
1

Kyoto University, Graduate School of Engineering, Department of Electrical Engineering, 2 Department of Electrical and Electronic Engineering, School of Engineering, Chukyo University, 3 Research Institute for Sustainable Humanosphere, Kyoto University
It is well known that spacecraft is charged by the background plasma in space. Since spacecraft charging is a cause of thedischarge and malfunction of electric equipment, spacecraft are usually designed to mitigate their surface charging.
However, a new concept of spacecraft orbital control using electromagnetic forces such as the Lorentz force and the Coulomb
force has been recently proposed. Spacecraft controls their orbit by controlling their potential using a charged-particle emitter.
Various applications of electromagnetic force as the primary means of spacecraft propulsion have been studied.
This orbital control method may provide propellantless orbital control and a very lightweight propulsion system comparedwith conventional chemical and electric propulsion systems.
Moreover, the system’s lifetime is not limited by propellant, so it can extend the spacecraft’s orbital lifetime.
To control the electromagnetic force that acts on the spacecraft, it is necessary to actively control the spacecraft’s electricalpotential.
In this paper, we investigate charging characteristics of active spacecraft charging in interplanetary space. by using 3D Full
Particle-in-cell simulation.
We particularly evaluate the effects of the solar wind velocity, beam-emission angle, and photoelectron emission on the spacecraft’s electric potential.
Additionally, we also investigate the charging characteristics of an electric solar wind sail, which is proposed as an applicationof electromagnetic orbital control in interplanetary space.
An electric solar wind sail consists of several-kilometer long, thin, conducting tethers.
Tethers are kept at a high positive potential on the order several kilo-volts by an electron gun.
The positively charged tethers deflect the momentum of solar wind protons which result in a propulsive force.
We analyze the dependency of the electric potential on the length and diameter of charged tethers, and evaluate the effect onthrust characteristics.
Keywords: Spacecraft Charing, Solar Wind, Electric Sail

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PEM26-19

Room:302

Time:May 24 15:15-15:30

Yin-Yang-Zhong: An overset grid for a sphere
KAGEYAMA, Akira1∗
1

Graduate School of System Informatics, Kobe University

Computation in a spherical region bounded by a constant radius is important in various fields of science and technology.
Spatial discretization inside a sphere is not simple because there is no orthogonal coordinate system that fits to a sphere, withouta coordinate singularity. The spherical polar coordinate system, for example, has two kinds of coordinate singularity; one on
the poles and another on the origin. Singularity should be avoided in numerical simulations because it causes grid convergencearound the singular point. We have developed a new grid system for a sphere, Yin-Yang-Zhong grid, which is an overset grid
system composed of Yin-Yang grid and Zhong grid. Yin-Yang grid itself is an overset grid system that covers the outer sphericalshell part inside the sphere. Zhong grid is a Cartesian grid-base system to cover the central part of the sphere. We have developed
a magnetohydrodynamic simulation code for a sphere based on the Yin-Yang-Zhong grid. The code is parallelized with MPI. We
have performed a quantitative tests of the code with diffusion and advection problems.
Keywords: Yin-Yang grid, overset grid, computer simulation, Yin-Yang-Zhong grid

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