| Budget Amount *help |
¥2,700,000 (Direct Cost: ¥2,700,000)
Fiscal Year 2006: ¥600,000 (Direct Cost: ¥600,000)
Fiscal Year 2005: ¥600,000 (Direct Cost: ¥600,000)
Fiscal Year 2004: ¥600,000 (Direct Cost: ¥600,000)
Fiscal Year 2003: ¥900,000 (Direct Cost: ¥900,000)
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| Research Abstract |
When a plasmoid with 1000 times density of the bulk plasma is heated by the electron heat flux, the ablation pressure reaches more than 100 times of the bulk plasma and subsequently makes the drift motion to the lower field side. The direction of the curvature vector is almost the major radius direction because a magnetic field faces to almost toroidal direction in tokamak. Then, the plasmoid with an extremely large pressure perturbation drifts due to a tire tube force induced by the difference between the inside circumference and the outside one of that perturbation. 1/R force induced by the magnetic field also makes such a drift motion. When an analytic model by integration of the force balance equation was constructed and was compared with simulation results, we have a very good agreement between the model and simulation results. On the other hand, when the pressure perturbation is very small, it is found that it has just an oscillation with no drift motion. When the perturbation is
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small, the linear theory is applicable to it. The linear theory predicts that the perturbation has just oscillation in stable equilibrium plasmas. Thus, small perturbation dose not have the drift motion. When a perturbation is large, the force balance is not satisfied any more and the linear theory can not be applicable. In other words, a large perturbation violating the linear theory is one essence of the drift motion. When more details are investigated about the drift motion, it is found that the top and bottom portions of the plasmoid drift to the higher field side, although the center of it drifts to the lower field side. The magnetic perturbation at the center of the plasmoid becomes negative due to diamagnetic current induced by the pressure perturbation. In other words, the magnetic field is removed from the center by the extremely large pressure perturbation.
Since that magnetic field removed is compressed at the edge of the plasmoid, the magnetic pressure perturbation becomes positive there. In such a case, the acceleration of the plasmoid becomes negative according to the analytic model described above, namely the edge of the plasmoid drifts to the higher field side.
When the initial plasmoids are located inside and outside of the torus in two characteristic poloidal cross sections in LHD plasma, it is found that the center of the plasmoids drift to the lower field side in all cases. In addition, it becomes clear that the portions with positive velocity and negative velocity in the major radius direction are alternately located along the flux surface. This fact is also verified in straight helical plasmas. Then, that fact may be induced by the helicity. Such an alternate location is most conspicuous when the plasmoid is located inside of the torus on the vertical elongated poloidal cross section, namely the highest field side. The physical meaning will be clarified in the future work. Less
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