Fig. 2-6 Analysis of microscopic behavior of plasma by computer simulation

(a) Vortices in a hot plasma. The vortices rotate counterclockwise changing shape. The heat in the plasma flows along the edges of vortices, transported from the center to the boundary of the plasma and lost. The red color shows equi-potential lines of positive electrostatic potentials and the blue color shows those of negative electrostatic potentials. The pattern reflects the local distribution of electric fields induced by plasma vortices.

(b) If we add clockwise rotation to the plasma shown in the left figure, large vortices split up into smaller ones and the induced electric field diminishes, accordingly the heat loss is reduced. This mechanism will improve plasma confinement.

Fig. 2-7

Vortices in the plasma (plasma turbulence) and heat transport. A model tokamak plasma composed of three million plasma particles is simulated by computer.

Computer simulation to explore the physics mechanisms underlying highly complicated behavior of high temperature plasmas is one of the very important areas of theoretical fusion plasma research. We have been conducting a detailed simulation study of the problem of thermal transport in a high temperature plasma to identify a physics mechanism that will explain how heat in the plasma escapes from a magnetically confined hot plasma region; a most important and still unsolved problem of plasma confinement. In this simulation study using a supercomputer, we have developed a tokamak plasma model composed of three million interacting plasma particles. A recent result has made it clear that the size of plasma vortices that occur in the plasma (plasma turbulence), an important factor that influences turbulent-induced heat losses of the plasma, becomes larger than previous theoretical predictions, and therefore it is possible to explain quantitatively the experimental data of heat losses on the basis of plasma turbulence. It is also found that the split up of vortices into smaller ones as shown in Fig. 2-7 may contribute to the significant improvement of plasma confinement observed recently in JT-60.

Reference Y. Kishimoto et al., Self-organized Critical Gradient Transport and Shear Flow Effects for Ion Temperature Mode in Toroidal Plasmas, 15th International Conference on Plasma Physics and Controlled Nuclear Fusion Research, Seville, Spain, IAEA-CN-60/D-2-II-3 (1994).

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