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Non-planar coil winding angle optimization for compatibility with non-insulated high-temperature superconducting magnets
Journal of Plasma Physics ( IF 2.5 ) Pub Date : 2020-10-20 , DOI: 10.1017/s0022377820001208
C. Paz-Soldan

The rapidly emerging technology of high-temperature superconductors (HTS) opens new opportunities for the development of non-planar non-insulated HTS magnets. This type of HTS magnet offers attractive features via its simplicity and robustness, and is well suited for modest size steady-state applications such as a mid-scale stellarator. In non-planar coil applications the HTS tape may be subject to severe hard-way bending strain ( $\epsilon _{\textrm {bend}}$ ), torsional strains ( $\epsilon _{\textrm {tor}}$ ) and magnetic field components transverse to the HTS tape plane ( $B_{\perp }$ ), all of which can limit the magnet operating space. A novel method of winding angle optimization is here presented to overcome these limitations for fixed input non-planar coil filamentary geometry. Essentially, this method: (i) calculates the peak $\epsilon _{\textrm {bend}}$ and $B_{\perp }$ for arbitrary winding angle along an input coil filamentary trajectory, (ii) defines a cost function including both and then (iii) uses tensioned splines to define a winding angle that reduces $\epsilon _{\textrm {tor}}$ and optimizes the $\epsilon _{\textrm {bend}}$ and $B_{\perp }$ cost function. As strain limits are present even without $B_{\perp }$ , this optimization is able to provide an assessment of the minimum buildable size of an arbitrary non-planar non-insulating HTS coil. This optimization finds that for standard 4 mm wide HTS tapes the minimum size coils of the existing HSX, NCSX and W7-X stellarator geometries are around 0.3–0.5 m in mean coil radius. Identifying the minimum size provides a path to specify a mid-scale stellarator capable of achieving high-field or high-temperature operation with minimal HTS tape length. For coils larger than this size, strain optimization allows use of wider (higher current capacity) HTS tapes or alternatively permitting a finite (yet tolerable) strain allows reduction of $B_{\perp }$ . Reduced $B_{\perp }$ enables a reduction of the HTS tape length required to achieve a given design magnetic field or equivalently an increase in the achievable magnetic field for fixed HTS tape length. The distinct considerations for optimizing a stellarator coilset to further ease compatibility with non-insulated HTS magnets are also discussed, highlighting relaxed curvature limits and the introduction of limits to the allowable torsion.

中文翻译:

与非绝缘高温超导磁体兼容的非平面线圈绕组角度优化

高温超导体 (HTS) 技术的迅速兴起为非平面非绝缘 HTS 磁体的发展开辟了新机遇。这种类型的高温超导磁体因其简单性和坚固性而具有吸引人的特性,非常适合中等尺寸的稳态应用,例如中型仿星器。在非平面线圈应用中,HTS 胶带可能会受到严重的硬向弯曲应变( $\epsilon _{\textrm {弯曲}}$ ), 扭转应变 ( $\epsilon _{\textrm {tor}}$ ) 和横向于 HTS 磁带平面的磁场分量 ( $B_{\perp }$ ),所有这些都会限制磁铁的工作空间。这里提出了一种新的绕组角度优化方法,以克服固定输入非平面线圈丝状几何形状的这些限制。本质上,这种方法: (i) 计算峰值 $\epsilon _{\textrm {弯曲}}$ $B_{\perp }$ 对于沿输入线圈丝状轨迹的任意缠绕角度,(ii) 定义包括两者的成本函数,然后 (iii) 使用张紧样条来定义缠绕角度,以减少 $\epsilon _{\textrm {tor}}$ 并优化 $\epsilon _{\textrm {弯曲}}$ $B_{\perp }$ 成本函数。因为即使没有应变限制也存在 $B_{\perp }$ ,这种优化能够提供对任意非平面非绝缘 HTS 线圈的最小可构建尺寸的评估。该优化发现,对于标准 4 mm 宽的 HTS 磁带,现有 HSX、NCSX 和 W7-X 仿星器几何形状的最小线圈尺寸平均线圈半径约为 0.3–0.5 m。确定最小尺寸为指定能够以最小 HTS 磁带长度实现高场或高温操作的中规模仿星器提供了一条途径。对于大于此尺寸的线圈,应变优化允许使用更宽(更高电流容量)的 HTS 带,或者允许有限(但可容忍)应变允许减少 $B_{\perp }$ . 减少 $B_{\perp }$ 能够减少实现给定设计磁场所需的 HTS 磁带长度,或者等效地增加固定 HTS 磁带长度的可实现磁场。还讨论了优化仿星器线圈组以进一步简化与非绝缘 HTS 磁体的兼容性的不同考虑因素,强调放宽的曲率限制和对允许扭转的限制的引入。
更新日期:2020-10-20
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