Confining energetic ions such as alpha particles is a prime concern in the design of stellarators. However, directly measuring alpha confinement through numerical simulation of guiding-center trajectories has been considered to be too computationally expensive and noisy to include in the design loop, and instead has been most often used only as a tool to assess stellarator designs post hoc. In its place, proxy metrics, simplified measures of confinement, have often been used to design configurations because they are computationally more tractable and have been shown to be effective. Despite the success of proxies, their correlation with direct trajectory calculations is known to be imperfect. In this study, we optimize stellarator designs for improved alpha particle confinement without the use of proxy metrics. In particular, we numerically optimize an objective function that measures alpha particle losses by simulating alpha particle trajectories. While this method is computationally expensive, we find that it can be used successfully to generate configurations with low losses.
高能粒子（如α粒子）的约束是仿星器设计中的首要问题。然而，通过数值模拟引导中心轨迹来直接测量α粒子约束，一直被认为计算成本过高且噪声过大，难以纳入设计循环，而通常仅用于对仿星器设计进行事后评估。取而代之的是，代理指标——即约束的简化度量——常被用于设计仿星器位形，因为它们在计算上更易处理，且已被证明是有效的。尽管代理指标取得了成功，但已知其与直接轨迹计算的相关性并不完美。在本研究中，我们绕开代理指标，直接针对改进α粒子约束进行仿星器优化。具体而言，我们通过模拟α粒子轨迹，数值优化一个度量α粒子损失的 objective 函数。尽管该方法计算成本高昂，但我们发现，它能够成功生成具有低损失率的仿星器位形。