TOWARDS THE ULTIMATE STORAGE RING-BASED LIGHT SOURCE

Present third generation synchrotron light sources reach brilliances in the 10 20 phot/s/0.1%BW/mm2/mrad2. Even if the trend in brilliance increase achieved over the last thirty years is over, a brilliance enhancement by two orders of magnitude can still be envisaged for an X-ray storage ring-based light source. The ESRF approach to a future machine delivering photons in the 0.5 - 500 keV range is presented in this paper. In particular, the choice of the energy, the comparison of circumference increase versus the use of damping wigglers to reach horizontal emittances in the low 10 -10 m.rad range, the possible lattices and the challenges made to the RF system by a very high stored current are reviewed. 1 MOTIVATION AND OBJECTIVES The construction and successful operation of the third generation synchrotron light sources has resulted in a significant improvement in the characteristics of the X- ray beams delivered to the Users. Now that these facilities are mature, it is legitimate to try to evaluate what the ultimate performances one can expect from a storage ring-based synchrotron radiation source are. The evaluation of their present performances and some expectations on their possible evolutions have already been reviewed on different occasions and in particular by A Wrulich (1) and in a recent edition of Synchrotron Radiation News, with H Winick as guest editor (2).