Study of beam fluctuation of high speed variably-polarizing undulator APPLE-2 in 2001 Dec.-2002 Nov.

Nakatani, Takeshi ; Agui, Akane; Yoshigoe, Akitaka ; Tanaka, Hitoshi*; Takao, Masaru*; Takeuchi, Masao*; Matsushita, Tomohiro*; Aoyagi, Hideki*

We measured the orbit fluctuation caused by APPLE-2 type undulator (ID23) installed in the SPring-8 storage ring by using the developed real time measurement system of electron and photon beam position monitors. We quantitatively found two characteristic fluctuations correlating with the ID23 motion by wavelet transform which is a kind of frequency analysis. One originates from the variation of error field during the ID drive. The other originates from the stray magnetic field leaked from the servomotors for the phase drive. Using these results, we tried to get rid of the effect of error fields on the beam orbit by the precise feed-forward correction table and the stray field shield. Consequently we succeeded in suppressing the orbit fluctuation down to sub-micron during the gap drive, which is observed by photon beam position monitors installed in downstream 20m from each light source point.