Study On The Effect Of Undulator Dynamic Field Integral And The Shimming Method

The dynamic field integral means the integrated magnetic field along the electron’s trajectory in an undulator, and will cause the tune shift, dynamic aperture reduction and beam lifetime shortening et al. The effect is inversely proportional to the square of the electron energy and proportional to the filed transverse roll-off. The field of the “Advanced Planar Polarized Light Emitter II(APPLE-II)” type Elliptical Polarization Undulator(EPU) has a very fast, intrinsic, transverse roll-off, especially for the vertical polarization mode, creating significant dynamic field integral effect to the beam motion. The research on the dynamic field integral effect of “APPLE-II” type EPU and the corresponding magnetic field shimming method is the hotspot in the field of international particle accelerator.As an intermediate energy synchrotron radiation light source, Shanghai Synchrotron Radiation Facility(SSRF) had not studied the effect of undulator dynamic field integral in Phase-I Project. But with more and more of the undulator’s operation, the effect of dynamic field integral will become serious and can not be ignored at all. SSRF storage ring has realized the “Top-up” injection operation, the effect of undulator dynamic field integral will reduce the beam’s injection efficiency, and evenly affect the stable operation of “Top-up” injection mode.A pair of EPUs(DEPU) with the period 58 mm and 148 mm, covering the energy ranges from 200 to 2000 e V and 20 to 200 e V, had been developed for the soft X-ray beam line for Angle Resolved Photoemission Spectroscopy(ARPES) and Photoemission Electron Microscopy(PEEM) at SSRF.In this dissertation, the study of DEPU dynamic field integral effect with different operation gap and different operation polarization mode using “Kick-Map” method is presented. The results of calculation show that: the tune drift is less than 0.0034 for EPU 58 in all operation polarization mode and all operation gap, which is acceptable to the stable operation of storage ring beam, the maximum tune shift is 0.016 for EPU 148 in vertical linear polarization mode and the minimum gap, which is not acceptable to the stable operation of storage ring beam, and the corresponding shimming of magnetic filed is necessary.The principle of “L-Shimming” method to reduce dynamic field integral effect for “APPLE-II” type EPU is also systematically stated in this dissertation. The optimization design of “L-Shimming” for EPU 148 dynamic field integral effect has been done with “RADIA Code”. The measurement results of flipping coil indicate that the magnetic field strength is coincident with the simulation result, and the error is less than 10% of the maximum shimming quantity. After shimming, the dynamic field integral effect of EPU 148 will reduce an order of magnitude.The machine study has been done after DEPU is installed in SSRF storage ring. The tune shift is less than 0.001 and the beam injection efficiency has almost not been influenced with EPU 148 in all operation polarization mode and all operation gap. It is proved that the shimming to reduce EPU 148 dynamic field integral effect is successful.