Interaction between electromagnetic field and pellet with shape transition due to nonisotropic ablation pressure

当具有1000倍体等离子体密度的等离子体团被电子热流加热时，烧蚀压力达到体等离子体的100倍以上，从而使漂移运动向低场侧移动。在托卡马克中，由于磁场几乎面向环形方向，所以曲率矢量的方向几乎是主要半径方向。然后，具有极大压力扰动的等离子体会由于该扰动的内周与外周之差所产生的轮胎内力而漂移。磁场产生的1/R力也会造成这种漂移运动。通过积分力平衡方程建立了分析模型，并与仿真结果进行了比较，结果表明该模型与仿真结果具有很好的一致性。另一方面，当压力扰动很小时，发现它只有一个振荡，没有漂移运动。当微扰为…时更小的是，线性理论适用于它。线性理论预言，在稳定的平衡等离子体中，微扰只有振荡。因此，小扰动不会产生漂移运动。当摄动较大时，力平衡不再满足，线性理论不再适用。换句话说，违反线性理论的大扰动是漂移运动的本质之一。当对漂移运动进行更详细的研究时，发现虽然等离子体的中心向低场方向漂移，但等离子体的顶部和底部向高场一侧漂移。由于压力扰动产生的抗磁电流，等离子体中心处的磁扰动变为负值。换言之，磁场被极大的压力扰动从中心移走，由于移出的磁场在等离子体的边缘被压缩，那里的磁压扰动变为正数。在这种情况下，根据上述解析模型，等离子体团的加速度变为负值，即等离子体团的边缘向高场侧漂移。在LHD等离子体的两个特征极向截面中，当初始等离子体团位于环面内外时，发现在所有情况下，等离子体团的中心都向低场侧漂移。此外，很明显，在大半径方向上具有正速度和负速度的部分交替地位于通量表面上。这一事实在直螺旋等离子体中也得到了证实。那么，这一事实可能是由螺旋度引起的。当等离子体团位于垂直拉长的极向截面上的环面内部，即最高场侧时，这种交替位置最为明显。物理意义将在今后的工作中得到澄清。较少

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 … More 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