The sag of mirror due to gravity induces unacceptable slope errors in beamline mirror-bending system of a synchrotron radiation facility

and approaches must be found to eliminate the unwanted gravity effect.According to the beam bending theory

the multi-point gravity compensation method is applicable.Taking an example of the bent collimating mirror for the XAFS beam-line(BL14W) at Shanghai Synchrotron Radiation Facility(SSRF)

the best position and value of the equilibrant were calculated through minimizing the gravity effect.With two

three and four points gravity compensation

slope errors were 0.179

0.067 and 0.032 μrad

respectively

i.e.the multi-point gravity compensation is better than the two-point gravity compensation

which is used for the Phase I beamlines of SSRF.The four-point gravity compensation method reduces more slope error and stress due to four support points.