Research and applications of bunch purity monitor at SSRF

Background The phase-II beam line project is currently under construction at Shanghai synchrotron radiation facility (SSRF), and one of its important goals is to have the ability of pumping experiments with high time resolution. High time resolution experiments require the purity of the probe bunch to reach the order of 10-5. However, the traditional bunch-by-bunch charge measurement based on the beam position monitor has a resolution of only 10-4. Purpose This study aims to propose and implement a bunch purity measurement system for high time resolution at SSRF. Methods Based on the time-correlated single-photon counting technology, a bunch purity monitor was developed and installed on the diagnostic beam line of SSRF. An evaluation experiment was designed to verify its performance and optimize this bunch purity measurement system. Results The experimental results show that the resolution of the new bunch purity monitor can reach to 10-7 in a few minutes. Conclusion The new bunch purity measurement system is