LEIR impedance model and coherent beam instability observations

The LEIR machine is the first synchrotron in the ion acceleration chain at CERN and it is responsible to deliver high intensity ion beams to the LHC. Following the recent progress in the understanding of the intensity limitations, detailed studies of the machine impedance started. In this work we describe the present LEIR impedance model, detailing the contribution to the total longitudinal and transverse impedance of several machine elements. We then compare the machine tune shift versus intensity predictions against measurements at injection energy and summarize the coherent instability observations in the absence of transverse feedback.