Optimized stellarator configurations and their analytical properties are obtained using a near-axis expansion approach. Such configurations are associated with good confinement as the guiding center particle trajectories and neoclassical transport are isomorphic to those in a tokamak. This makes them appealing as fusion reactor candidates. Using a direct coordinate approach, where the magnetic field and flux surface functions are found explicitly in terms of the position vector at successive orders in the distance to the axis, the set of ordinary differential equations for first and second order quasisymmetry is derived. Examples of quasi-axisymmetric shapes are constructed using a pseudospectral numerical method. Finally, the direct coordinate approach is used to independently verify two hypotheses commonly associated with quasisymmetric magnetic fields, namely that the number of equations exceeds the number of parameters at third order in the expansion and that the near-axis expansion does not prohibit exact quasisymmetry from being achieved on a single flux surface.

中文翻译：

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使用直接坐标法构建准对称仿星器

使用近轴扩展方法获得优化的仿星器配置及其分析特性。这种配置与良好的约束相关，因为引导中心粒子轨迹和新古典传输与托卡马克中的那些同构。这使得它们作为聚变反应堆的候选者很有吸引力。使用直接坐标方法，其中磁场和通量表面函数是根据到轴的距离上连续阶的位置向量明确找到的，推导出一阶和二阶拟对称的常微分方程组。准轴对称形状的示例是使用伪光谱数值方法构建的。最后，