Research on fast pre-tuning method of 9-cell superconducting cavities
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摘要: 对频率和场平坦度的预调谐是9-cell超导腔耗时最多的后处理工序之一,很快将成为国内相关大科学工程9-cell腔批量生产的瓶颈。首先介绍了9-cell超导腔两种常用的预调谐方法,即DESY方法和Cornell方法的原理,建模分析和比较了两种方法的计算精度和误差来源,给出Cornell方法调谐量计算的修正。然后结合9-cell超导腔预调谐实验研究,给出了快速预调谐方法:DESY的重建算法在低场平时精度较高且收敛迅速,可作为粗调;Cornell微扰算法在高场平时精度较高且测量迅速,可作为微调。结合两种调谐方式,将预调谐分为粗调和微调两步,可有效提升9-cell超导腔预调谐的速度。Abstract: The pre-tuning of frequency and field flatness is one of the most time-consuming post-processing procedures for 9-cell superconducting cavities, and will soon become the bottleneck of mass production of 9-cell cavities in domestic related major scientific projects. In this paper we firstly introduce two commonly used pre-tuning methods for 9-cell superconducting cavities, namely DESY method and Cornell method. Then we analyze and compare their calculation accuracy and error sources by modeling, and make a correction on the Cornell method’s tuning amount calculation. Verifing the pre-tuning of several cavities by the experimental research, we give a fast pre-tuning method in which DESY reconstruction algorithm is used for coarse-tuning as it has high precision and rapid tuning speed in low field flatness and Cornell perturbation algorithm is used for fine-tuning as it has high precision in high field flatness with faster measurement. Combining these two tuning algorithms, the pre-tuning is divided into two steps: coarse tuning and fine tuning, which can effectively improve the pre-tuning speed of the 9-cell superconducting cavity.
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Key words:
- 9-cell superconducting cavity /
- pre-tuning /
- field flatness /
- bead pull measurement
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表 1 DESY与Cornell预调谐方法微扰量计算结果对比
Table 1. Comparison of perturbation calculation results between DESY and Cornell pre-tuning method
cell
numberperturbation
amount $ {e}_{\mathrm{r}\mathrm{e}\mathrm{f}}/{10}^{-4} $perturbation amount
$ {e}_{\mathrm{D}\mathrm{E}\mathrm{S}\mathrm{Y}}/{10}^{-4} $perturbation amount
$ {e}_{\mathrm{C}\mathrm{o}\mathrm{r}\mathrm{n}\mathrm{e}\mathrm{l}\mathrm{l}}/{10}^{-4} $1 5 4.96 6.21 2 4 3.93 4.18 3 −4 −4.03 −4.84 4 2 2.02 1.90 5 −3 −2.99 −2.70 6 2 2.03 1.97 7 −1 −0.99 −1.35 8 −4 −3.99 3.50 9 6 6.02 5.92 表 2 DESY与Cornell预调谐方法微扰量计算结果百分比误差对比
Table 2. Comparison of perturbation percentage error of DESY and Cornell pre-tuning method
cell
numberpercentage error
$ {E}_{\mathrm{D}\mathrm{E}\mathrm{S}\mathrm{Y}} $/%percentage error
$ {E}_{\mathrm{C}\mathrm{o}\mathrm{r}\mathrm{n}\mathrm{e}\mathrm{l}\mathrm{l}} $/%1 −0.84 24.14 2 −1.87 4.61 3 0.71 20.96 4 0.94 −4.94 5 −0.47 −9.98 6 1.41 −1.42 7 −1.46 35.15 8 −0.03 −12.49 9 0.25 −1.26 表 3 DESY和Cornell方法计算微扰量的均方根误差随场分布变化趋势
Table 3. Perturbation RMS error of DESY and Cornell method with different field flatness
field
flatness/%RMSE
$ {\eta }_{\mathrm{d}\mathrm{e}\mathrm{s}\mathrm{y}}/{10}^{-4} $RMSE
$ {\eta }_{\mathrm{C}\mathrm{o}\mathrm{r}\mathrm{n}\mathrm{e}\mathrm{l}\mathrm{l}}/{10}^{-4} $60 0.055 2.11 70 0.076 2.74 80 0.033 0.96 90 0.015 0.45 表 4 场平调节至95%时不同方法调谐时间对比
Table 4. Pre-tuning time of different methods for 95% field flatness (FF)
method number of cells tuned measure time/h tuning time/h total time/h Cornell only 22 (FF > 95%) 0.2 6.6 6.8 DESY only 9 (FF < 90%) 0.6 2.7 3.3 combined method 13 (FF > 95%) 0.9 3.9 4.8 -
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