Fast Vertical Single-bunch Instability at Injection in the CERN SPS: An Update

Following the first observation of a fast vertical instability for a single high-brightness bunch at injection in the SPS in 2002, a series of detailed measurements and simulations has been performed in order to assess the resulting potential intensity limitations for the SPS, as well as possible cures. During the 2006 run, the characteristics of this instability were studied further, extending the intensity range of the measurements, and comparing the experimental data with simulations that take into account the latest measurements of the transverse machine impedance. In this paper, we summarize the outcome of these studies and our understanding of the mechanisms leading to this instability. The corresponding intensity limitations were also determined.