Baseline recovery method to measure bunch charge under low-current mode of SSRF

The top-up injection mode of Shanghai Synchrotron Radiation Facility(SSRF) needs precise measurement of the beam bunch charges.This is performed by an integration current transformer,but the beam current is too low to neglect the background noise.In order to wipe out the noise coming from the ground loops,the adaptable polynomial fitting method is used to extract the baseline,instead of using the constant background or the linear background model. Test results show that the system resolution can be improved...