MHD Stability of Fusion Plasma with Ferromagnetic Wall Effect

发展聚变演示堆的两个重要问题是高β等离子体的实现和低活度材料的开发。对于低活性材料，铁素体钢被认为是最有前途的演示堆结构材料。然而，铁素体钢由于其很强的铁磁性，也被认为对等离子体的点火、控制、MHD稳定性和等离子体约束等产生了不良影响。其中，MHD稳定性与高β等离子体的实现直接相关，铁素体钢有可能恶化MHD稳定性，降低临界β值。因此，研究铁磁效应对MHD稳定性的影响是聚变堆发展中的重要问题之一。本研究的目的是通过对低高宽比圆截面平衡…的磁流体力学稳定性分析，研究铁磁效应对临界β的影响更多地使用线性MHD稳定代码，它使用全套电阻MHD方程。研究结果表明：对于高宽率为3的托卡马克，铁磁性效应对相对磁导率为2和3的铁磁壁的临界β减少量分别为8%和20%，对于大长径比托卡马克，相对于相对磁导率为2的铁磁壁的减少量为10%，而对于铁磁效应对临界β的减小值较小。结果表明，壁面中铁磁性引起的扰动极向磁场的吸引使外扭结模式失稳，并降低了临界β值；对于长径比为3的托卡马克，在由环形等离子体旋转和等离子体耗散共同作用打开的阻性壁的小半径处存在稳定窗口，而对于高深宽比托卡马克则没有观察到稳定窗口。结果表明，当相对磁导率小于3时，稳定窗口宽度变宽，而当相对磁导率大于3时，稳定窗口宽度减小。稳定效应来自于不稳定模与稳定模的耦合，而稳定模的缩减率因铁磁性而降低。较少

Two important issues in developing the fusion DEMO reactor are the realization of high beta plasma and the development of low activation materials. As for the low activation materials, the ferritic steel is considered to be the most promising candidate as the structural material in DEMO reactor. Because of its strong ferromagnetism, however, the ferritic steel is also considered to have a bad influence to plasma ignition, control, MHD stability and plasma confinement etc.. Among others, MHD stability is related directly to the realization of high beta plasma, and the ferritic steel has possibility to deteriorate MHD stability and decrease the critical beta value. It is, therefore, one of the most important issues in development of fusion reactor to investigate the ferromagnetic effect on the MHD stability. The purpose of this study is to investigate the effect of ferromagnetic effect on critical beta by MHD stability analyses for low aspect ratio and circular cross section equilibrium … More using linear MHD stability code, which uses the full set of resistive MHD equations. The obtained results in these studies are in the following :The reduction of critical beta by the effect of ferromagnetism is shown to be 8 % and 20 % against the ferromagnetic wall of relative permeability of 2 and 3, respectively, for tokamaks of aspect rate 3. The reduction value is 10 % against the ferromagnetic wall of relative permeability of 2 for high aspect ratio tokamaks, and the toroidal effect is considered to be small for ferromagnetic effect on the critical beta. It is shown that the attraction of the perturbed poloidal magnetic field due to ferromagnetism in the wall destabilizes the external kink mode, and reduces the critical beta values.The existence of the stability window in the minor radius of resistive wall opened by both effects of the toroidal plasma rotation and the plasma dissipation is shown for tokamaks of aspect ratio 3, while they have not been observed for high aspect ratio tokamaks. The width of stability window is shown to be widened in small values of relative permeability less than 3, while it is shown that the width of stability window is reduced in large values of relative permeability greater than 3. The stabilization effect comes from the coupling the unstable mode to the stable mode, whose reduction rate is decreased by the ferromagnetism. Less