Research on fast pre-tuning method of 9-cell superconducting cavities

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.