[P-EM37_30PM2] Structure and Dynamics of the Magnetosphere

[PEM37-P08_PG] 3D Full kinetic simulations of plasma flow interaction with meso- and micro-scale magnetic dipoles

3-min talk in an oral session

*Hideyuki USUI¹, Yasumasa ASHIDA², Iku SHINOHARA³, Masao NAKAMURA⁴, Hiroshi YAMAKAWA², Yohei MIYAKE¹ (1.Graduate school of system engineering, Kobe University, 2.Research Institute for Sustainable Humanosphere, 3.Japan Aerospace Exploration Agency/Institute of Space and Astronautical Science, 4.Osaka Prefecture University)

Keywords:Magnetic dipole, Meso-scale, Plasma response, Boundary current layer, Plasma particle simulation

Plasma flow response to a magnetic dipole and the resulting formation of a magnetosphere depends on the intensity of the magnetic moment of the dipole. In this study, we examined plasma flow interactions with a magnetic dipole which is much smaller than the Earth's intrinsic magnetic dipole by performing three-dimensional full Particle-In-Cell simulations. The size of a magnetic dipole immersed in a plasma flow is characterized by distance L from its center at which the equilibrium is satisfied between the pressure of the magnetic field of the dipole and that of the plasma flow. In the Earth's magnetosphere, L implies the magnetopause location. We particularly focused on meso- and micro-scale magnetic dipoles in which L is comparable to and smaller than the gyroradius of ions in the flow. In the meso-scale case, ions kinetics should be dominantly considered while electrons whose gyroradius is sufficiently small can be treated as fluid. In the micro-scale, however, electrons as well as ions should be treated particles because L becomes small and the electron kinetics cannot be ignored either. Our interest is in the formation of current layer at the magnetosphere boundary in the both scales. Corresponding to the formation of a magnetosphere, the boundary current also depends on the size of the magnetosphere. In the meso-scale case, the boundary current is dominated by the electron diamagnetic current at the large density gradient found at the distance of L. This signature is similar to the case of the Earth's magnetosphere. In the micro-scale case, however, the trajectories of ions and electrons gyration play an important role to determine the boundary current. Since the ion's gyroradius is larger than L, charge separation between ions and electrons occurs in the upstream region. As particles approach to the inner dipole, the electron gyroradius becomes small and electron drift motion becomes dominant. It is also confirmed that static electric field caused by the charge separation affect the plasma dynamics and the resulting current flow.