Abstract A mirror machine with a minimum B field for MHD stability is an option for a steady-state compact fusion neutron source design. A previous calculation of an idealized quadrupolar mirror field in Ref Agren and Moiseenko (2017) is extended to a magnetic field which smoothly evolves to expander regions beyond the mirror throats. In a minimum B field, the projection of a flux surface on planes perpendicular to the magnetic axis evolves from a circular shape at the mid-plane to a highly elliptical shape as the mirror ratio is increased. Magnetic shaping is made to find the minimal ellipticity. The ellipticity depends sensitively on the gyro center magnetic drift in the confinement region, and the optimal result approaches a state where the magnetic drift is made as small as possible, which corresponds to the SFLM (Straight Field Line Mirror) field. In such a magnetic field, in combination with a weak radial electric field, each guiding center is forced to move close to its mean magnetic surface, thereby suppressing neoclassical transport effects. Biased end plates, placed at the end tank outside the confinement region, is a tool to control the radial electric field. The biased end plates could also assist to more precisely determine the positioning of drift surfaces in the confinement region. The reproduction of the optimized magnetic field with superconducting coils is a challenge due to the strong gradients in B. This is solved by a special arrangement with compact 3D superconducting coils, and the reproduction of the magnetic field is demonstrated with a mirror ratio of 4. Mirror ratios exceeding 10 may be reachable with finite β effects included. Analytical expressions in closed form are derived.

中文翻译：

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最小 B 陷阱的磁性整形

摘要 具有最小 B 场以实现 MHD 稳定性的镜面机是稳态紧凑聚变中子源设计的一种选择。先前在 Ref Agren 和 Moiseenko (2017) 中对理想化四极镜场的计算扩展到磁场，该磁场平滑地演变为超出镜喉的扩展区域。在最小 B 场中，磁通表面在垂直于磁轴的平面上的投影随着镜比的增加从中间平面处的圆形演变为高度椭圆形。进行磁性整形以找到最小椭圆度。椭圆度敏感地依赖于约束区内的陀螺中心磁漂移，最佳结果接近磁漂移尽可能小的状态，它对应于 SFLM（直线场线镜）场。在这样的磁场中，结合微弱的径向电场，每个引导中心被迫靠近其平均磁表面移动，从而抑制了新古典输运效应。偏置端板放置在限制区域外的端罐上，是控制径向电场的工具。偏置端板还可以帮助更精确地确定限制区域中漂移表面的定位。由于 B 中的强梯度，使用超导线圈再现优化的磁场是一项挑战。 这是通过具有紧凑型 3D 超导线圈的特殊布置来解决的，并且磁场的再现以镜像比为 4 来演示。在包含有限 β 效应的情况下，可以达到超过 10 的镜面比。导出封闭形式的解析表达式。