Compared to Nb₃Sn- and NbTi-wound superconducting undulators (SCUs), MgB₂-wound SCUs are of interest for future electron synchrotron beam light sources owing to their higher temperature operating margin and associated stability. In this study, a three-period undulator consisting of twelve racetrack coils wound with 2nd generation (2 G) multifilamentary advanced-internal-magnesium-infiltration MgB₂ strands were fabricated and tested in liquid and gaseous helium (He) over a temperature range of 4.2 K–20 K. The coil winding cross sections (in each coil) were 5 mm wide and 4.8 mm thick. At 4.2 K, a critical current (I _c) of 325.7 Amps produced a maximum undulator bore field of 1.19 T. It should be noted that the short, 3-period nature of the coil led to an asymmetry in the field profile (the maximum positive field was 1.19 T, the maximum negative was −0.25 T), suggesting a peak field of 0.72 T in the absence of end effects. Finite element modeling (FEM) results of simulations for a one meter long undulator of otherwise identical design gave 0.85 T (larger because of higher currents enabled by the lower field). But in any case, the I _c value coil reached is 94% of that of the short sample (dictated by the 1.19 T positive field for the coil as tested). FEM was performed to study the magnetic field profile, which was validated experimentally. The magnetic field was measured using a Hall probe which was translated along the beam axis during measurement to explore the spatial field variation along the beam travel direction. The spatially alternating field was asymmetric, and the maximum field was more prominent in the positive direction than in the negative direction, the difference being due to broken symmetry, that is, short coil end effects. In this work, we show useful fields are possible for MgB₂ undulators; the use of such conductors can allow a larger thermal margin and enable conduction-cooled operation.

中文翻译：

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三周期小尺寸 2G AIMI MgB2 平面波荡器的开发和测试


与 Nb ₃ Sn 和 NbTi 缠绕超导波荡器 (SCU) 相比，MgB ₂ 缠绕 SCU 由于其更高的温度工作裕度而成为未来电子同步加速器束光源的关注点以及相关的稳定性。在这项研究中，由十二个跑道线圈组成的三周期波荡器由第二代 (2 G) 多丝先进内部镁渗透 MgB ₂ 股线缠绕而成，并在液态和气态氦气 (He ）在 4.2 K–20 K 的温度范围内。线圈绕组横截面（每个线圈中）为 5 毫米宽和 4.8 毫米厚。在 4.2 K 时，325.7 安培的临界电流 ( _c ) 产生了 1.19 T 的最大波荡器孔场。应该指出的是，线圈的短 3 周期特性导致了场分布（最大正场为 1.19 T，最大负场为 -0.25 T），表明在没有末端效应的情况下峰值场为 0.72 T。对其他相同设计的一米长波荡器的有限元建模 (FEM) 仿真结果给出了 0.85 T（较大，因为较低的磁场产生了较高的电流）。但无论如何，线圈达到的 _c 值是短样本的 94%（由测试线圈的 1.19 T 正磁场决定）。采用有限元法研究磁场分布，并通过实验验证。使用霍尔探头测量磁场，在测量过程中霍尔探头沿光束轴平移，以探索沿光束行进方向的空间场变化。 空间交变场是不对称的，最大场在正方向比负方向更突出，这种差异是由于对称性破缺，即短线圈末端效应造成的。在这项工作中，我们展示了 MgB ₂ 波荡器可能存在的有用场；使用这种导体可以允许更大的热裕度并实现传导冷却操作。