Direct evidence of microstructure dependence of magnetic flux trapping in niobium.
Direct evidence of microstructure dependence of magnetic flux trapping in niobium.
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DOI：
10.1038/s41598-021-84498-x
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发表时间：
2021-03-08
影响因子：
4.6
通讯作者：
Lee PJ
中科院分区：
文献类型：
--
作者：
Balachandran S;Polyanskii A;Chetri S;Dhakal P;Su YF;Sung ZH;Lee PJ
元素II型超导铌是现代粒子加速器、光源、探测器、传感器和量子计算架构中使用的超导射频腔的首选材料。在射频应用中提高能量效率的一个基本挑战是由于在冷却过程中由于不完全的磁场排出而被捕获的残余磁场引起的功率耗散。使用表面掺杂技术的新SRF腔处理配方显著提高了其低温效率。然而，SRF Nb加速器的性能仍然显示出对捕获磁场的脆弱性。在这份手稿中，我们报告的观测的直接联系之间的磁通捕获和不完整的磁通驱逐与空间变化的微观结构内铌。平均晶粒尺寸为10-50 µm的细晶粒再结晶微观结构导致磁通捕获，即使在晶粒内部缺乏位错结构。超过100-400 μm的较大晶粒尺寸不会导致优先通量捕获，正如磁光成像直接观察到的那样。虽然磁光成像的局部磁通量变化提供了清晰的微观结构水平，批量变化也表明钉扎力曲线与顺序热处理研究的变化。关键结果表明，铌微结构的完全控制将有助于生产更高性能的超导谐振器，减少与磁通量捕获相关的射频损耗1。
Elemental type-II superconducting niobium is the material of choice for superconducting radiofrequency cavities used in modern particle accelerators, light sources, detectors, sensors, and quantum computing architecture. An essential challenge to increasing energy efficiency in rf applications is the power dissipation due to residual magnetic field that is trapped during the cool down process due to incomplete magnetic field expulsion. New SRF cavity processing recipes that use surface doping techniques have significantly increased their cryogenic efficiency. However, the performance of SRF Nb accelerators still shows vulnerability to a trapped magnetic field. In this manuscript, we report the observation of a direct link between flux trapping and incomplete flux expulsion with spatial variations in microstructure within the niobium. Fine-grain recrystallized microstructure with an average grain size of 10–50 µm leads to flux trapping even with a lack of dislocation structures in grain interiors. Larger grain sizes beyond 100–400 µm do not lead to preferential flux trapping, as observed directly by magneto-optical imaging. While local magnetic flux variations imaged by magneto-optics provide clarity on a microstructure level, bulk variations are also indicated by variations in pinning force curves with sequential heat treatment studies. The key results indicate that complete control of the niobium microstructure will help produce higher performance superconducting resonators with reduced rf losses1 related to the magnetic flux trapping.
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