Vertical Emmittance Studies at the ATF Damping Ring

A primary purpose of the ATF Damping Ring is to demonstrate the small vertical emittance required for a future linear collider. In this report, we first describe the diagnostics available to measure this emittance. Then we discuss the dependence of the emittance on various parameters, such as the betatron tunes, vacuum pressure, and beam current, and, subsequently, study several methods of betatron-coupling correction. Next, we show that the interferometer used to determine the vertical beam size is sensitive to transverse beam tails and does not measure the core emittance, which could explain the observed sensitivity of the measured spot size to vacuum pressure and beam intensity. Finally, we summarize the results and propose a few further studies. In the appendix, we present recent measurements of the dynamic aperture, and discuss the variation of the beta functions, e.g., at the synchrotron light monitor, with the betatron tune. Here, we also present details of the SUSSIX program, by which, in the future, we hope to infer all linear coupling parameters as well as higher-order nonlinearities from turn-by-turn orbit data.