National Institutes of Natural Science, National Institute for Fusion Science
Department of Helical Plasma Research, Fundamental Physics Simulation Research Division

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"Impurity transport caused by
blob and hole propagations"
H. Hasegawa and S. Ishiguro,
Nuclear Fusion Vol. 57, in press (2017)

In this study, the dynamics between impurity ions and the blob and hole structures have been investigated with the three-dimensional electrostatic particle-in-cell simulation. The simulations have shown the following facts: (1) The dipolar profile of impurity ion density in the blob / the hole is formed. (2) Such a density profile propagates with the blob/ the hole. (3) The effective radial diffusion coefficient for impurity ions by a single blob / hole is comparable to the Bohm diffusion coefficient (the figure shows impurity ion tranport by a blob).
"Study of self-consistent particle flows
in a plasma blob with particle-in-cell simulations"
H. Hasegawa and S. Ishiguro,
Physics of Plasmas Vol.22, 102113 (2015)

In this study, the presence of the spiral current system composed of the diamagnetic and parallel currents in a blob is confirmed by the particle simulation without any assumed sheath boundary models (see the left figure). Furthermore, we have observed that the temperature structure in a blob is formed by the potential structure (see the electron velocity distributions in the right figure).
"Molecular dynamics and Monte Carlo hybrid simulation for fuzzy tungsten nanostructure formation"
A.M. Ito, A. Takayama, Y. Oda, T. Tamura, R. Kobayashi, T. Hattori, S. Ogata, N. Ohno, S. Kajita, M. Yajima, Y. Noiri, Y. Yoshimoto, S. Saito, S. Takamura, T. Murashima, M. Miyamoto and H. Nakamura,
Nuclear Fusion Vol.55, 073013 (2015)
Fuzzy nanostructure on the surface of tungsten materials is generated by exposure to helium plasma. The formation process of the fuzzy nanostructure had been successfully reproduced by Molecular Dynamics and Monte-Carlo hybrid (MD-MC hybrid) simulation.
"Effects of trapped electrons on ion reflection in an oblique shock wave"
M. Toida and J. Inagaki,
Physics of Plasmas Vol.22, 062305 (2015)

A magnetosonic shock wave propagating obliquely to the magnetic field can trap electrons and accelerate them to ultrarelativistic energies. These electrons excite multi- dimensional fluctuations, which significantly influence electron motions.
Effects of trapped electrons on ion motions in an oblique shock wave have been investigated with particle simulations. It is found that the number of accelerated ions via reflection from the shock front is increased because of the multi-dimensional fluctuations excited by the trapped electrons. The figure shows the phase space plots of ions [(b) 2Ds] and test ions [(c) 1Dt] which do not feel multi-dimensional fluctuations. The ions with vx > vsh are reflected.
"Formation of large-scale structures with sharp density gradient through Rayleigh-Taylor growth in a two-dimensional slab under the two-fluid and finite Larmor radius effects"
R. Goto, H. Miura, A. Ito, M. Sato, and T. Hatori,
Physics of Plasmas Vol.22, 032115 (2015)
Density contours in a 2D extended MHD simulation of the Rayleigh-Taylor instability. It is observed that the secondary Kelvin-Helmholtz-type instability forms fine wavy structures along the density contours.
"Multi-Hierarchy Simulation of Collisionless Driven Reconnection by Real-Space Decomposition"
S. Usami, R. Horiuchi, H. Ohtani, and M. Den,
Journal of Physics: Conference Series Vol.561, 012021 (2014)

Spatial profiles of the magnetic field lines. By means of our multi-hierarchy simulations, the influence of macroscopic dynamics on microscopic physics of magnetic reconnection is investigated. Dynamical behaviours of reconnection that is, steay reconnection (Fig.(a)) or intermittent reconnection (Fig. (b)) depend sensitively on plasma inflows from the MHD domain.
"Structure transitions induced by the Hall term in homogeneous and isotropic
magnetohydrodynamic turbulence"
H. Miura and K. Araki,
Physics of Plasmas Vol.21, 072313 (2014)
Isosurfaces of the enstrophy density (colored) and the current density (grey) in freely decaying homogeneous and isotropic Hall MHD turbulence in a simulation of 10243 grid points.
"Suppression effects of Weibel instability for fast electron divergence"
H. Sakagami, T. Johzaki, T. Taguchi and K. Mima,
EPJ Web of Conference Vol.59, 17016 (2013)

As the growth rate of the Weibel instability is absolutely large, little suppression effects can be expected even if the background electron temperature increase to more than 100 keV. This magnetic field does not remain at rest and shows turbulent behaviors, enhancing the divergence of fast electrons. To control the location of Bz, punched out targets are introduced, where many vacuum holes are punched out as shown in left Figure. Background electrons that carry the return current can only flow in the gaps between holes, because the sheath field prevents them from crossing over the hole. Thus stable magnetic fields are induced and grow up to almost ±300 MG, which are shown in right figure. Fast electrons go forward with a meandering motion, and reduction of divergence can be expected. Unfortunately, this structure simultaneously disturbs fast electron propagation, and the fast electron beam intensity also decreases because the number of electrons in such energy range is reduced.
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