Multiple space-time scales are contained in motions of plasma, thereby, it is difficult to fully and effectively describe plasma phenomena with one physical model. So it is the beaten track to perform simulations with different physical models depending on scales (macroscopic and microscopic scales). However, it is tough work to achieve unified understanding of phenomena with simulations separated by scales. Then, high-temperature fusion plasma is a typical example of above difficult issues.
Aiming unified understanding of plasma motions which cross the hierarchal wall, our group researches and develops a multi-hierarchy simulation model which treats some scales simultaneously.

Figure shows the multi-hierarchy simulation result of magnetic reconnection. The left and right panels display magnetic field lines and fluid velocity vectors. The multi-hierarchy model is progressed from the previous model as follows. First, the boundary condition in the downstream is improved from periodic to open, so then outflow can go out across the downstream boundary. Furthermore, non-uniform space grids are adopted in the macro hierarchy so as to calculate larger region.

The hierarchy-interlocking in the upstream direction of magnetic reconnection has been discussed in the previous multi-hierarchy model. Aiming to apply our multi-hierarchy model to a larger system of magnetic reconnection, we need to develop the hierarchy-interlocking model in the downstream direction. As the first step, using new interlocking method, we perform a multi-hierarchy simulation in which plasma flow with a Maxwellian velocity distribution propagates from the micro to the macro hierarchies. Figure shows bird’s-eye view of the plasma mass density. We can see that plasmas are smoothly and continuously ejected from the PIC to the MHD domains.

1. S. Usami, H. Ohtani, R. Horiuchi, and M. Den: "Simulation of Plasma Flow Injection with Multi-Hierarchy Model Aiming Magnetic Reconnection Studies" Communications in Computational Physics 11 1006-1021 (2012)
2. S. Usami, R. Horiuchi, H. Ohtani, and M. Den: "Development of Multi-Hierarchy Simulation Model with Non-Uniform Space Grids for Collisionless Driven Reconnection" Physics of Plasmas 20 061208(2013)
3. H. Miura and K. Araki, "Coarse-graining study of homogeneous and isotropic Hall magnetohydrodynamics turbulence" Plasma Physics and Controlled Fusion 55 014012-1 (2013)