An improved current potential method for fast computation of stellarator coil shapes
An improved current potential method for fast computation of stellarator coil shapes
复制标题
一种用于快速计算仿星器线圈形状的改进电流势方法
DOI：
10.1088/1741-4326/aa57d4
复制
发表时间：
2016
期刊：
影响因子：
3.3
通讯作者：
M. Landreman
中科院分区：
文献类型：
--
作者：
M. Landreman
几种快速计算仿星器线圈形状的方法进行了比较，包括经典的NESCOIL程序（默克尔1987年核聚变27 867），其推广使用截断奇异值分解，和Tikhonov正则化方法，我们称之为REGCOIL中的平方电流密度是包括在目标函数。考虑到W7-X和NCSX的几何形状，以及任何所需的正则化水平，我们发现REGCOIL方法同时实现了较低的表面平均和最大值的电流密度（线圈绕组表面）和正常的磁场（在所需的等离子体表面）。因此，这种方法可以同时改善目标等离子体形状的自由边界重建，同时大幅增加线圈之间的最小距离，防止线圈之间的碰撞，同时改善端口的访问和维护。REGCOIL方法还允许对正则化水平进行更精细的控制，它保留了凸性以确保找到的局部最优值是全局最优值，并且它消除了NESCOIL的两种病态：所得线圈形状变得与用于参数化线圈表面的角度的任意选择无关，并且所得线圈形状随着傅立叶分辨率的增加而收敛而不是发散。因此，我们认为，REGCOIL应该被用来代替NESCOIL的应用程序中，需要一个快速和强大的方法线圈计算，如在固定边界等离子体优化线圈的复杂性为目标时，或范围新的仿星器的几何形状。
Several fast methods for computing stellarator coil shapes are compared, including the classical NESCOIL procedure (Merkel 1987 Nucl. Fusion 27 867), its generalization using truncated singular value decomposition, and a Tikhonov regularization approach we call REGCOIL in which the squared current density is included in the objective function. Considering W7-X and NCSX geometries, and for any desired level of regularization, we find the REGCOIL approach simultaneously achieves lower surface-averaged and maximum values of both current density (on the coil winding surface) and normal magnetic field (on the desired plasma surface). This approach therefore can simultaneously improve the free-boundary reconstruction of the target plasma shape while substantially increasing the minimum distances between coils, preventing collisions between coils while improving access for ports and maintenance. The REGCOIL method also allows finer control over the level of regularization, it preserves convexity to ensure the local optimum found is the global optimum, and it eliminates two pathologies of NESCOIL: the resulting coil shapes become independent of the arbitrary choice of angles used to parameterize the coil surface, and the resulting coil shapes converge rather than diverge as Fourier resolution is increased. We therefore contend that REGCOIL should be used instead of NESCOIL for applications in which a fast and robust method for coil calculation is needed, such as when targeting coil complexity in fixed-boundary plasma optimization, or for scoping new stellarator geometries.