Abstract
Collective effects, such as the microwave instability, influence the longitudinal dynamics of an electron beam in a storage ring. In a storage ring free electron laser (FEL) they can compete with the induced beam heating and thus be treated as a further concomitant perturbing source of the beam dynamics. Bunch length and energy spread measurements, carried out at the Super-ACO storage ring, can be correctly interpreted according to a broad-band impedance model. Quantitative estimations of the relative role that is played by the microwave instability and the laser heating in shaping the beam longitudinal dynamics have been obtained by the analysis of the equilibrium laser power. It has been performed in terms of either a theoretical limit, implemented with the measured beam longitudinal characteristics, or the numerical results obtained by a macroparticle tracking code, which includes the laser pulse propagation. Such an analysis, carried out for different operating points of the Super-ACO storage ring FEL, indicates that the laser heating counteracts the microwave instability.
Highlights
Free electron lasers (FEL) are tunable coherent sources of radiation with a spectral range extending from the infrared to the vacuum ultraviolet (VUV)
FEL oscillators, the laser oscillation is originated by the interaction between a charged bunch passing through the FEL straight section and a light pulse that is confined in an optical cavity, provided that the perfect synchronism condition is achieved
The laser amplification mechanism is produced to the detriment of the kinetic energy of the charged beam: a fraction of it is converted in the FEL light pulse energy
Summary
LURE, Université Paris-Sud, bâtiment 209D, BP 34 91898 Orsay, France and Technische Universteit Eindhoven, Eindhoven, The Netherlands. Quantitative estimations of the relative role that is played by the microwave instability and the laser heating in shaping the beam longitudinal dynamics have been obtained by the analysis of the equilibrium laser power It has been performed in terms of either a theoretical limit, implemented with the measured beam longitudinal characteristics, or the numerical results obtained by a macroparticle tracking code, which includes the laser pulse propagation. Such an analysis, carried out for different operating points of the Super-ACO storage ring FEL, indicates that the laser heating counteracts the microwave instability
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