Following up on earlier work which demonstrated an improved numerical stellarator coil design optimization performance by the use of stochastic optimization (Lobsien et al., Nucl. Fusion, vol. 58 (10), 2018, 106013), it is demonstrated here that significant further improvements can be made – lower field errors and improved robustness – for a Wendelstein 7-X test case. This is done by increasing the sample size and applying fully three-dimensional perturbations, but most importantly, by changing the design sequence in which the optimization targets are applied: optimization for field error is conducted first, with coil shape penalties only added to the objective function at a later step in the design process. A robust, feasible coil configuration with a local maximum field error of 3.66 % and an average field error of 0.95 % is achieved here, as compared to a maximum local field error of 6.08 % and average field error of 1.56 % found in our earlier work. These new results are compared to those found without stochastic optimization using the FOCUS and ONSET suites. The relationship between local minima in the optimization space and coil shape penalties is also discussed.

中文翻译：

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改进仿星器线圈设计优化的性能

跟进早期的工作，该工作通过使用随机优化（Lobsien）证明了改进的数值仿星器线圈设计优化性能等。,核。融合, 卷。58 (10), 2018, 106013)，这里证明了可以对 Wendelstein 7-X 测试用例进行显着的进一步改进——降低现场误差并提高稳健性。这是通过增加样本量和应用全三维扰动来完成的，但最重要的是，通过改变应用优化目标的设计顺序：首先进行场误差优化，仅将线圈形状惩罚添加到目标中在设计过程的后续步骤中发挥作用。与我们早期工作中发现的最大局部磁场误差为 6.08% 和平均磁场误差为 1.56% 相比，此处实现了具有 3.66% 的局部最大磁场误差和 0.95% 的平均磁场误差的稳健、可行的线圈配置. 这些新结果与未使用 FOCUS 和 ONSET 套件进行随机优化的结果进行了比较。还讨论了优化空间中的局部最小值与线圈形状惩罚之间的关系。