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1.3 GHz纯铌腔首先经过EP(Electro-Polishing)重抛处理,以便去除表面的机械损伤层,抛光厚度在120微米左右。然后进行800 °C维持3 h的退火,去除铌材中吸附的氢。接着进行20 μm的轻抛,去除表面氧的扩散层。将上述预处理之后得到的纯铌腔进行超声清洗1 h,之后通过高压纯水清洗(High Pressure Rinsing, HPR)清洗40 min,含HF的活化液浸泡10 min,然后用超纯水把残酸彻底清洗干净,并立即进行纯铌腔的电化学镀膜。需要注意的是,由于铌在空气中表面很快会形成新的氧化层而影响膜基结合力。因此,活化液处理后的10 min内采取纯水冲洗5遍,保证残留酸液全部冲洗干净,否则会影响后续的镀膜质量。之后迅速加入电镀液接通直流电源,开始镀腔工作。
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纯铌腔的电镀采用恒流法,椭圆异型电极(见图4)做阳极,整腔赤道处缠绕铜带做阴极,采用青铜合金电镀液,电流大小为2.1 A,电镀时间为4 h,电镀速率0.05 μm/min,然后大量水冲洗后晾干。其中,青铜合金电镀液采用的配方如表1所列。
药品名称 药品纯度 添加量/(g·L−1) 生产厂家 柠檬酸 AR 160 西陇化工 氢氧化钾 AR 120 西陇化工 碱式碳酸铜 AR 16 阿拉丁 锡酸钾 AR 20 阿拉丁 磷酸二氢钾 AR 17 西陇化工 -
电化学镀膜结束后,将密封的镀膜腔放到高真空退火炉中退火。在退火程序中设定温度为700 °C(20 h),升温速率0.5 °C/min,自然降温,加热真空小于10−3 Pa。退火炉上下有两个温度探头控制炉体的温度,保证整个退火过程中镀膜腔处于均温区内。热处理的实际升温曲线和气压随时间变化关系如图5所示,可以看出升温到700 °C的过程中气压逐渐降低,最后趋于稳定。
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退火完成后青铜层抛光可采取BCP(Buffered Chemical Polishing)或者EP进行操作,BCP抛光配方为:HNO3(65%~68%)和H3PO4
$(\geqslant $ 99%)比例为1:3的混合酸进行抛光30 min,需要注意的是抛光中会产生大量的NO2气体,必须在通风橱中佩戴防护服进行操作。EP时采用H3PO4$(\geqslant $ 99%)和正丁醇($\geqslant $ 99%)比例为3:2的混合液,在50 mA/cm2通电的情况下进行操作。通过对抛光后的薄膜腔表面进行观察,确保青铜杂质层彻底去除干净后,用大量纯水冲洗干净,然后晾干。
Study on Nb3Sn Coating Technology of 1.3 GHz Superconducting Cavity by Electrochemical Bronze Method
doi: 10.11804/NuclPhysRev.40.2022031
- Received Date: 2022-03-11
- Rev Recd Date: 2022-04-06
- Publish Date: 2023-03-20
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Key words:
- RF superconductivity /
- coating /
- Nb3Sn /
- electrochemistry
Abstract: 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 1 100 °C, 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 °C, 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
Citation: | Ming LU, Feng PAN, Didi LUO, Chunlong LI, Shuai WU, Tongtong ZHU, Qingwei CHU, Shichun HUANG, Andong WU, Teng TAN, Hao GUO. Study on Nb3Sn Coating Technology of 1.3 GHz Superconducting Cavity by Electrochemical Bronze Method[J]. Nuclear Physics Review, 2023, 40(1): 51-57. doi: 10.11804/NuclPhysRev.40.2022031 |