论文标题
使用优化的近轴扩展来映射准对称恒星的空间
Mapping the space of quasisymmetric stellarators using optimized near-axis expansion
论文作者
论文摘要
证明了一种方法可以快速计算准轴对称和准螺旋的对称恒星剂的形状和特性。在这种方法中，优化应用于磁性水动力平衡和准对称的方程，该方程在与磁轴的距离很小的距离上扩展，如Garren和Boozer [Phys [phys》中。流体B，3，2805（1991）]。由于方程式通过扩展减少了方程，计算成本大大降低到1 CPU秒的阶段，从而在参数空间上实现了宽和高分辨率的扫描。与传统的恒星优化相反，此处的成本函数可最大程度地提高扩展准确的体积。成本函数的关键术语是$ || \ nabla \ mathbf b || $，以最大化字段中的比例长度。使用此方法，计算并显示了$ 5 \ times 10^5 $优化配置的数据库。观察到的准对称构型存在于连续的频段中，磁轴长与平均主要半径的比率有所不同。发现了几种定性类型的配置类型，包括准螺旋对称字段，其中字段周期数为两个或六个以上。
A method is demonstrated to rapidly calculate the shapes and properties of quasi-axisymmetric and quasi-helically symmetric stellarators. In this approach, optimization is applied to the equations of magnetohydrodynamic equilibrium and quasisymmetry, expanded in the small distance from the magnetic axis, as formulated by Garren and Boozer [Phys. Fluids B, 3, 2805 (1991)]. Due to the reduction of the equations by the expansion, the computational cost is significantly reduced, to times on the order of 1 cpu-second, enabling wide and high-resolution scans over parameter space. In contrast to traditional stellarator optimization, here the cost function serves to maximize the volume in which the expansion is accurate. A key term in the cost function is $|| \nabla\mathbf B ||$, to maximize scale lengths in the field. Using this method, a database of $5\times 10^5$ optimized configurations is calculated and presented. Quasisymmetric configurations are observed to exist in continuous bands, varying in the ratio of the magnetic axis length to average major radius. Several qualitatively new types of configuration are found, including quasi-helically symmetric fields in which the number of field periods is two or more than six.
