Full kinetic simulations on plasma and field disturbancein the vicinity of spacecraft
H. Usui
Graduate School of System Informatics, Kobe University, 1-1 Rokko-dai, Nada, Kobe 657-8501, Japanh-usui@port.kobe-u.ac.jp

Space exploration and utilization have been rapidly increasing, and a strong demand arises
regarding comprehensive understanding of interactions between spacecraft system and its
surrounding plasma environment. We have been studying plasma and field disturbance causedby the spacecraft-plasma interactions as well as active plasma emission from spacecraft byperforming full kinetic simulations with the Particle-In-Cell (PIC) method. In this presentation,
we introduce some of the simulation results on the interactions between spacecraft system andspace plasma. We would particularly like to focus on plasma flow response to a meso-scale
magnetic dipole in Magneto-Sail (MS) propulsion system. The MS system was proposed as oneof the innovative interplanetary flight systems and its propulsion can be obtained through thesolar wind plasma interactions with the artificially created magnetic dipole around spacecraft.
The plasma flow response to a magnetic dipole and the resulting formation of a magnetospheredepends on the intensity of the magnetic moment of the artificial dipole field. When the size ofthe magnetic dipole is comparable to or somewhat smaller than the ion Larmor radius or theinertial length, we call it meso-scale and the plasma kinetics such as finite Larmor radius effectwill play an important role to determine the plasma response to the magnetic dipole. Contrary to
the case of the Earth's magnetosphere, we found that difference of dynamics between ions andelectrons in the meso-scale dipole field plays an important role in the magnetosphere formation[1]. The width of the boundary current layer as well as the spatial gradient of the local magnetic
field compression found at the dayside can be characterized by the electron Larmor radius. Asan application, we also examined the solar wind interactions with a magnetic anomaly called
Reiner Gamma found on the lunar surface. The simulation results show that some ions arereflected back to the sunward direction over Reiner Gamma even though the ion Larmor radius
is larger than the scale of magnetic anomaly, which basically agrees with the KAGUYA
spacecraft observation [2]. To investigate such multi-scale phenomena caused by the differenceof dynamics between electrons and ions, we developed a new electromagnetic PIC code byincorporating the Adaptive Mesh Refinement (AMR) technique called PARMER [3]. The
AMR technique is one of promising methods which can realize high-resolution analysis bymaking use of dynamically and locally refining calculation meshes when the phenomena arehighly localized and involves coupled physical multi-scale. At the end of the presentation, wewould like to touch upon PARMER development.
[1] T. Moritaka, Y. Kajimura, H. Usui, M. Matsumoto, T. Matsui and I. Shinohara, Physics ofPlasmas,19, 032111(2012).
[2] Y. Saito, S. Yokota, T. Tanaka, K. Asamura, M. N. Nishino, M. Fujimoto, H. Tsunakawa, H.
Shibuya, M. Matsushima, H.Shimizu, F. Takahashi, T. Mukai and T. Terasawa, GeophysicalResearch Letters 35 (24) (2008).
[3] H. Usui, M. Nunami, T. Moritaka, T. Matsui, Y. Yagi, Procedia Computer Science 4 (2011)
2337–2343.