1.3 GHz超导腔的电化学青铜法铌三锡镀膜技术

Study on Nb3Sn Coating Technology of 1.3 GHz Superconducting Cavity by Electrochemical Bronze Method

由于射频超导腔具有高品质因数Q0,大束流孔径等诸多优势,已被加速器行业广泛应用。目前纯铌腔的性能已经接近理论极限,使用Nb3Sn薄膜腔代替纯铌腔是突破这一限制的有效手段。铌三锡具有较高的超导转变温度和过热磁场,理论预期可以大幅度提高SRF腔体工作温度和加速梯度。目前,Nb3Sn薄膜制备技术蓬勃发展,其中锡蒸汽扩散法已经比较成熟,已制备出初步满足工程需求的铌基铌三锡薄膜射频超导腔。但是由于反应温度在1100℃以上,锡蒸汽扩散法无法摆脱纯铌基底,因此不可避免地在机械稳定性、导热性等方面有缺陷,难以满足未来高可靠性加速器的应用。青铜法广泛应用于铌三锡线缆的制备,热处理温度不高于700℃,具有制备铜基铌三锡镀膜腔的潜力。此外,电化学镀膜与其他方式相比,具有成本低、反应过程容易控制、常温常压等明显优势。本工作将上述两种工艺结合起来,研究了电化学方式在1.3 GHz铌基超导腔上镀青铜前驱体,之后热处理合成铌三锡薄膜腔。垂测结果表明,4.2 K下的薄膜腔本征Q0为6×108左右且仍具很大提升空间。

Superconducting RF cavities have been widely used in modern accelerators because of their advanced characters,such as high quality factor,large beam aperture etc.After years of development,the performance of bulk Nb cavity is close to the material's theoretical limit.Using Nb3Sn thin film cavities to replace current bulk Nb cavities could be a viable way to break such limit.Because of its high superconducting transition temperature and superheating magnetic field,Nb3Sn can elevate both the working temperature and the acceleration gradient of the SRF cavities.Currently,there are several preparation methods of Nb3Sn thin films under development.Among them,Nb3Sn thin films with decent performance were successfully prepared on the inner surface of Nb cavity by tin vapor diffusion method.However,because the reaction temperature is above 1100℃,tin vapor diffusion method cannot get rid of bulk niobium substrate,so it inevitably has defects in mechanical stability,thermal conductivity and other aspects,which is difficult to meet the application of high reliability accelerator in the future.Bronze method have been successfully used for Nb3Sn cable preparation.The maximum heat treatment temperature of this method is under 700℃,which can potentially be applied to copper-based Nb3Sn thin film cavity preparation.In addition,electrochemical coating method is also considered because of its advantages,such as low cost,easy control of reaction process,normal temperature and pressure.In this work,we combined the advantages of above two methods.Specifically,on 1.3 GHz Nb based cavity,bronze precursor films were prepared by electrochemical plating firstly,and then were heated to synthesize Nb3Sn thin film by annealing.The vertical test results show that the intrinsic Q0 of the film cavity at 4.2 K is about 6×108 and still has a lot of room for improvement.