22E03
Multi-scale particle-in-cell simulation of solar wind interaction in an artificial
small-scale magnetosphere
小型磁気圏-太陽風相互作用に関するマルチスケール粒子シミュレーション	 
Toseo Moritaka, Masanori Nunami, Hideyuki Usui and Tatsuki Matsui
森高	  外征雄, 沼波	  政倫，臼井	  英之，松井	  竜樹Institute of Laser Engineering, Osaka University
Yamada-oka, Suita, Osaka 565-0871, Japan
大阪大学レーザーエネルギー学研究センター 〒565-0871	  大阪府吹田市山田丘
In order to investigate the magnetic inflation and solar wind interaction processes in an artificial
magnetosphere, we have developed a multi-scale particle-in-cell simulation code with adaptive meshrefinement technique. These processes are relevant to the propulsive mechanism of Magneto-Plasma Sail(MPS), which is one of the next generation interplanetary flight systems. We confirm that the multi-scale
simulation code could describe the three dimensional plasma dynamics around the MPS in a reasonable
numerical cost by allocating the refined grids near the center of the magnetosphere.

1. Introduction
Magneto-plasma sail (MPS)[1] is one of thenext generation interplanetary flight systems, andnow considered in Japan Aerospace Exploration
Agency (JAXA). Two plasma processes areapplied for the propulsive mechanism of MPS
without fuel consumption. One is scattering ofsolar wind plasmas by an artificial magnetosphere,
which is created by a hoop coil carried inside thespacecraft[2]. The other is expansion of themagnetosphere by means of plasma injection
from the spacecraft. This process is called“magnetic inflation”[3].
We have been developed a full particle-in-cellsimulation code with adaptive mesh refinement
technique (AMR) in order to evaluate the potencyof these mechanisms applied to MPS[4,5].
Injected plasmas would generate a high-density
region in the vicinity of the spacecraft, andrequired grid size in such region is much smaller
than the typical scales of plasma phenomena
expected in the solar wind. In the AMR
simulation, fine grids are allocated locally in thehigh-density region and the other region isevaluated by using moderate size grids. Therefore,
the numerical cost is dramatically reduced
compared to the simulations using uniform grids.
2. Simulation model
The developed multi-scale simulation code isbased on the three-dimensional electromagnetic
particle-in-cell method. The simulation domain isstructured hierarchically. Time step intervals aswell as grid sizes are defined according to thehierarchy levels. High and low levels correspond to
the fine and coarse grid systems, respectively. As

the system evolves, some grids in a hierarchy
domain (Level L) are removed according to thelocal conditions and corresponding grids in thehigher hierarchy domain (Level L+1) are newly
produced as the divided grids.
3. Simulation results

Fig.1. Grid arrangement and current density profile
resulting from AMR simulations in two differentrefinement criteria. Red and yellow lattices represent
refined and coarse grid regions, respectively.

Figure 1 shows the hierarchical grid arrangement(lattice) and the induced current density profile(color contour) resulting from the simulations of
two-dimensional solar wind interaction[5]. The
induced current density structure is importantbecause the repulsion between induced current andcoil current densities results in the propulsion[6].
Two different refinement criteria are used here. One
is based on the spatial position of each grid (panel(A)). Grids near the coil center are refined
initially, and the grid arrangement is left unchanged.
The other is based on the local magnitude of theinduced current density (panel (B)). Grids are
dynamically refined according to the time
evolutions of induced current density. The observed
current density structures are almost identical inthese two simulations. This result indicates that thenumerical boundaries between different hierarchies
hardly affect the simulation results.
Figure 2 shows the simulation results for thethree-dimensional solar wind interaction including
the magnetic inflation. Refined grids are produced
along with the high-density region near the coilcenter generated due to the plasma injection. As aresult of three-dimensional solar wind interaction,
the injected plasmas flow away from the center ofthe magnetosphere with an asymmetric density
structure.

Fig.2. Birds-eye views of ion density profile (colorcontour) from two different angles. Some magnetic fieldlines and refined grid arrangement are represented as
green lines and blue lattices, respectively. Solar windflow and magnetic moment of coil current density aredirected in x- and z-directions, respectively.

Acknowledgments
The present study was supported by CREST(JST). Computations were performed using thePlasma Simulator at the National Institute forFusion Science (NIFS10KTBT018) and the KDK
system of RISH at Kyoto University.
References[1] H. Yamanaka, I.Funaki et al: Acta Astronautica. 59(2006) 777.
[2] R. Zubrin and R. Andrews: Journal of Spacecraft andRockets. 28 (1991) 197.
[3] R. Winglee, J.Slough et al: Journal of GeophysicalResearch. 105 (2000) 67.
[4] T. Moritaka, M.Nunami et al: Journal of Plasma andFusion Research SERIES. 9 (2010) 586.
[5] T. Moritaka, M.Nunami et al: Plasma and Fusion
Research. 6 (2011) 2401101.
[6] T. Moritaka, H.Usui et al: Physics of Plasmas,submitted.