Control of the electron beam vertical instability using the super-ACO free electron laser

The operation of the Super-ACO storage ring FEL using a harmonic RF cavity exhibits vertical instabilities, which are generally compensated with an increase of the chromaticity of the operating point. It has been previously reported that the FEL itself can compete, and even damps various types of electron beam instabilities. Here, we show that, when the FEL is operating, the threshold of appearance of the vertical instability is modified and that the FEL enlarges the zone of stable regime of the beam operation. Experiments showing the evolution of the chromaticity allowing the beam to be stable versus current are compared, in the presence of the FEL or for the natural beam operation.