Theoretical and Computer-Simulation Studies

Fusion plasmas as well as space and astrophysical plasmas are many-body systems in which innumerable charged particles interact through the electromagnetic force. Their dynamics involve strong nonlinearity, and exhibit complex and complicated behaviors. Nonlinear phenomena in such plasmas exceed the limitations of conventional theoretical analyses, and hence, computer simulation, the third methodology following theory and experiment, plays an important role in studying plasma physics. simulation studies are broadly divided into five stages: (1) total planning and formulation of computational models, (2) development of simulation methods and codes (3) execution of simulations, (4) analysis and feedback of results, (5) construction of a theoretical framework. To advance these in a coordinated manner, we have established the Simulation Lab., the Visualization Lab., and other facilities. We are also developing efficient data-analysis methods that use advanced virtual-reality-technology in order to enable an easier understanding of simulation results having complex space-time structures.

Magnetohydrodynamic(MHD) instability in the LHD

Based on a three-dimensional equilibrium of LHD obtained by computer simulation, we conduct Linear and nonlinear simulations of MHD instability driven by pressure gradients.

Analysis of divertor Plasmas

  We are advancing analysis of divertor plasmas in a three-dimensional equilibrium configuration of the LHD using a fluid model. We are also verifying the validity of the fluid approach by means of particle simulations.

The TAE Mode and High-Energy Ion Transport

Using simulations that implement the kinetic effects of particles, we are studying the toroidal Alfven eigenmode(TAE mode)excited by high-energy ions in a tokamak, and have obtained results that can reproduce experimental observation of the TAE bursts.

Relaxation in a Spherical tokamak

In computer simulations of a spherical tokamak, we observed the process of self-organization in which relaxation termed the internal reconnection event (IRE) was triggered by nonlinear development of MHD instability driven by the pressure gradient, and the destroyed configuration spontaneously recovered.

Generation and Reversal of the Dipole Magnetic Field

By means of numerical simulations, we have verified that when MHD thermal convection is induced in a rotating spherical shell, a dipole magnetic field is produced and maintained under certain conditions. When the computations were continued for a longer time period while maintaining the state driven by the thermal convection, it was learned that the dipole field experienced repeated reversal at irregular intervals (intermittent reversal).

Crystallization and Self-organization of Polymers

We are conducting simulations of polymer dynamics into the crystallization of polyethylene as one example of many-body systems exhibiting interactions (covalent bonds and intermolecular force) that differ from that of plasmas through the electromagnetic force. Despite the differences in interactions, the process of crystallization shows intermittent structural changes similar to those observed in plasmas.

Visualization Using the CompleXcope Virtual-reality System

Results obtained by simulations of a various nonlinear phenomena usually have extremely complex spatiotemporal structures. Comprehending these structures through analysis using conventional computer graphics is quite difficult. CompleXcope projects stereo images in a cubical room of approximately three meters on a side, and researchers carry out their analyses inside this virtual-reality space. Visualizing data using this system makes even complex structure instantly comprehensible.

Result > Theoretical and Computer-Simulation Studies
Result > Theoretical and Computer-Simulation Studies