A study was conducted to understand and optimize the coating process of NbSn thin film superconducting radio-frequency (SRF) cavities using the tin (Sn) vapor diffusion method. The characterization of nanometer-scale Sn droplets, millimeter-scale Sn spots, and locally extremely thin patchy areas was carried out. The causes of their occurrence were analyzed, and their influence on RF performance was distinguished and clarified. Furthermore, a method of achieving high-quality NbSn films was explored by increasing the adsorption of residual Sn vapor to suppress the generation of nanometer-scale Sn droplets while under the premise of ensuring uniform film growth by increasing the Sn vapor flux. It was seen that the performance of the 1.3 GHz single cell NbSn SRF cavity coated at IMP was significantly enhanced after the optimization of the coating process with a maximum accelerating gradient (E) of over 18 MV/m and an unloaded quality factor (Q) of more than 1 × 10 at E = 12 MV/m and 4.2 K. This study provides quantitative insights for understanding the coating process and provides an essential reference for coating high-performance NbSn SRF cavities using the Sn vapor diffusion method.

中文翻译：

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锡蒸气扩散法射频Nb3Sn薄膜超导腔体涂覆工艺的理解与优化

进行了一项研究，以了解和优化使用锡 (Sn) 蒸气扩散法的 NbSn 薄膜超导射频 (SRF) 腔的涂层工艺。对纳米级锡滴、毫米级锡点和局部极薄的斑片区域进行了表征。分析了它们发生的原因，并区分和明确了它们对射频性能的影响。此外，在提高Sn蒸气通量保证薄膜生长均匀的前提下，通过增加对残余Sn蒸气的吸附来抑制纳米级Sn液滴的产生，探索了获得高质量NbSn薄膜的方法。可以看出，经过优化镀膜工艺后，在 IMP 镀膜的 1.3 GHz 单电池 NbSn SRF 腔体的性能显着增强，最大加速梯度 (E) 超过 18 MV/m，空载品质因数 (Q)在 E = 12 MV/m 和 4.2 K 时超过 1 × 10。这项研究为理解涂层工艺提供了定量见解，并为使用 Sn 蒸汽扩散法涂层高性能 NbSn SRF 腔提供了重要参考。