Design of a compact aberration-free achromatic 90 deg.-bend system for the ELSA accelerator

New beam lines for the production of picosecond hard X-rays are under development at the ELSA facility, a high brightness l-20 MeV electron accelerator. One major concern in the design of the new lines is to preserve as much as possible the high quality of the electron beam, while making very compact transport components. We present in this paper, the design of a very compact achromatic 90 deg.-bend system that will be used to transport the electron beam in the new experimental areas. This study led us to propose an original sextupole configuration to correct geometrical aberrations in both horizontal and vertical planes