Beam instability observations and analysis at SOLEIL

The paper describes measurement and analysis of beam instability made at SOLEIL in comparison with the expectation using numerically estimated impedance budget. A multibunch beam is found to be under a strong influence of resistive-wall and fast beam-ion instabilities, in a way that largely depends on the local position in a bunch train. For a single bunch, the measured reactive impedance turns out to be larger by nearly a factor of two than calculated in all three planes. The roughness impedance due to NEG coating is assessed as a possible cause.