Compensations of double elliptical polarization undulator effects on the SSRF storage ring

A pair of Apple-II type EPU (double elliptical polarization undulators, DEPU) was installed in the SSRF storage ring. The unwanted integral magnetic field errors induced by the devices lead to closed-orbit distortions (COD), tune shifts, coupling variation, reduction of the dynamic aperture and so on. These effects deteriorate the operation performance of the SSRF. Feedforward tables of corrector coils, quadrupoles and skew quadrupoles are used to correct the COD, tune shifts and coupling, respectively. The max COD keeps smaller than 10 m, the tune shifts keep around 0.001 and the coupling keeps 0.1%. Sextupole strengths were optimized to restore the dynamic aperture, the injection efficiency resumes to more than 80%. In the nearly 4 years operation, the compensations have been working well, and there are still more and more supplements and revisions of the feedforward tables in development for the COD corrections.