Mechanical stability of the magnet girder assembly at the SSRF

Electron beam stability is very important for third-generation light sources, especially for the Shanghai Synchrotron Radiation Facility (SSRF), whose ground vibration is much larger than other light sources. The mechanical stability of the magnet girder assemblies (MGAs) in a storage ring is essential for electron beam stability and performance. In order to improve the mechanical stability of the R&D MGAs in the storage ring of the SSRF, the number of MGAs in each lattice cell has been modified from three to five, and the girder structure has been optimized. Vibration measurements have been performed on the modified MGA prototype (the longest and heaviest MGA in the cell) to investigate mechanical stability and the influence of cooling water on magnet vibration. Measurement results show that the modified MGA has improved the first eigenfrequency from 5.9 Hz in R&D time to 21.9 Hz in the lateral and 22.5 Hz in the vertical direction; it has a good mechanical stability performance compared with other third-generation light source projects; and the influence of cooling water on the magnet vibration is about 4%, less than that of the ground vibration.