Comparison of predicted and measured collective effects in a fourth generation storage ring

Predicting, measuring, and mitigating collective instabilities in storage rings is important to maximize their performance. We will describe our efforts to theoretically compute and characterize collective effects during the design process, and how these continue during early operations. We then show how these predictions compare to measured collective effects at the APS-U, both with and without the harmonic cavity to lengthen the bunch.out using the harmonic cavity to lengthen the bunch.