Measurement of betatron function at the Photon Factory

The betatron functions (Β functions) of the Photon Factory storage ring (PF-ring) at KEK have been measured in the normal operation mode and in the low emittance mode. The measured values of the Β functions agree with their theoretical values very well. When the vertical wiggler (VW) is excited up to 4.5 T, tune shifts are produced by about 0.04 and the Β functions are distorted considerably. A simple mathematical model was made by assuming the VW to consist of three rectangular magnets with the sextupole field component. It was possible to explain the tune shifts and to give a good estimate of the distortion of the Β functions. The local correction was also applied to reduce the distortions by changing the focal strengths of the quadrupole magnets adjacent to the VW