Understanding particle drifts in a non-symmetric magnetic field is of primary interest in designing optimized stellarators in order to minimize the neoclassical radial loss of particles. Quasisymmetry and omnigeneity, two distinct properties proposed to ensure radial localization of collisionless trapped particles in stellarators, have been explored almost exclusively for magnetic fields with nested flux surfaces. In this work, we examine radial particle confinement when all field lines are closed. We then study charged particle dynamics in the special case of a non-symmetric vacuum magnetic field with closed field lines obtained recently by Weitzner & Sengupta (Phys. Plasmas, vol. 27, 2020, 022509). These magnetic fields can be used to construct magnetohydrodynamic equilibria for low pressure. Expanding in the amplitude of the non-symmetric fields, we explicitly evaluate the omnigeneity and quasisymmetry constraints. We show that the magnetic field is omnigeneous in the sense that the drift surfaces coincide with the pressure surfaces. However, it is not quasisymmetric according to the standard definitions.

中文翻译：

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具有闭合磁力线的非对称磁场 X 点附近的带电粒子动力学

了解非对称磁场中的粒子漂移对于设计优化的仿星器以最大限度地减少粒子的新古典径向损失至关重要。准对称性和全能性是为确保仿星器中无碰撞俘获粒子的径向定位而提出的两个不同特性，几乎专门针对具有嵌套通量表面的磁场进行了探索。在这项工作中，我们检查了所有场线闭合时的径向粒子约束。然后，我们研究了 Weitzner 和 Sengupta 最近获得的具有闭合磁力线的非对称真空磁场的特殊情况下的带电粒子动力学（物理。等离子, 卷。2020 年 27 月 27 日，022509）。这些磁场可用于构建低压的磁流体动力学平衡。扩展非对称场的幅度，我们明确地评估了全能性和准对称性约束。我们表明，在漂移表面与压力表面重合的意义上，磁场是无所不在的。但是，根据标准定义，它不是准对称的。