Impedance Database II for the Advanced Photon Source storage ring

The first impedance database constructed at the advanced photon source was successfully used in reproducing the main characteristics of single-bunch instabilities observed in the storage ring. However, the finite bandwidth of the corresponding impedance model was limited to 40 GHz, which happens to be the resolution limit of the density modulation observed in the microwave instability simulation. In order to resolve simulation results never verified in the experiments, we decided to extend the calculated bandwidth of impedance to 100-200 GHz by recalculating the wake potentials excited by a shorter bunch. Since low-order electromagnetic code requires 20-40 grid points per wavelength, reducing the bunch length required a large number of grids for the 3D structure. We used bunch lengths of 1- and 2-mm in the Gaussian distribution in the impedance database II project. For the large-scale computation we used the 3D electromagnetic code GdfidL for wake potential calculation at the cluster equipped with 240 GB of memory. The resultant wake potential excited by the short bunch together with application to the storage ring for collective effects is presented in this paper.