Abstract:
Background The High Energy Photon Source (HEPS), as a high-brightness fourth-generation synchrotron radiation facility, requires superior beam orbit stability. During commissioning, a beam orbit shift with a characteristic frequency of 2.5 Hz was observed, which motivated a systematic investigation of possible disturbance sources. The vacuum chamber cooling water system was considered as one possible mechanical source because of its possibility for water-flow-induced vibration.
Purpose This study focuses on whether the cooling water system of the HEPS storage-ring vacuum chambers can act as a direct mechanical excitation source for the observed 2.5 Hz beam orbit shifts.
Methods A combined approach of computational fluid dynamics (CFD) simulation, modal analysis and experimental vibration testing was adopted. The VC01 vacuum chamber was selected for detailed analysis because it contains typical water jackets and local cooling channels. Transient flow simulations based on the Large Eddy Simulation (LES) model were used to analyze pressure pulsations in the cooling channels. A high-precision, non-contact laser Doppler vibrometer was used to measure the vibration response under water-flow and no-flow conditions and comparative water on/off tests were also conducted for several types of vacuum chambers in a standard sector.
Results The CFD simulations predicted that cooling water flow generates pressure pulsations, with frequencies mainly distributed in the 15-300 Hz range. Experimental measurements showed clear amplification in the 13-100 Hz band when the cooling water was active. No anomalous energy peak was observed near the specific 2.5 Hz frequency of beam orbit shifts in either the simulations or the experimental data.
Conclusions The results indicate that the vacuum chamber cooling water system is unlikely to be the direct mechanical excitation source of the observed 2.5 Hz beam orbit shifts. However, the water-flow-induced vibration in the 13-100 Hz band should still be considered in the future optimization of vacuum chamber support and cooling-channel design.
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