Recent developments in measurement and tracking of the APS storage ring beam emittance.

The x-ray pinhole camera is used at the APS storage ring to measure the beam emittance. The measured data are archived during user operation. At 1 Hz bandwidth, we have achieved better than 1 µm stability in the measured horizontal beam size, typically of 143 µm, corresponding to 8 nm-rad. During user runs, beam size variations up to 2.5 µm were observed (corresponding to emittance variations of 0.4 nm-rad), which were strongly correlated and attributed to the variation of electron energy loss in the insertion devices. In other words, the user-initiated insertion device gap changes are the major factor in observed beam emittance variations during user runs. [ABSTRACT FROM AUTHOR]