DLSR design and plans: an international overview

Abstract

It has been known for decades that the emittance of multi-GeV storage rings can be reduced to very small values using multi-bend achromat (MBA) lattices. However, a practical design of a ring having emittance approaching the diffraction limit for multi-keV photons,i.e.a diffraction-limited storage ring (DLSR), with a circumference of order 1 km or less was not possible before the development of small-aperture vacuum systems and other accelerator technology, together with an evolution in the understanding and accurate simulation of non-linear beam dynamics, had taken place. The 3-GeV MAX IV project in Sweden has initiated a new era of MBA storage ring light source design,i.e.a fourth generation, with the Sirius project in Brazil now following suit, each having an order of magnitude smaller horizontal emittance than third-generation machines. The ESRF, APS and SPring-8 are all exploring 6-GeV MBA lattice conversions in the imminent future while China is considering a similar-energy green-field machine. Other lower-energy facilities, including the ALS, SLS, Soleil, Diamond and others, are studying the possibility of such conversions. Future larger-circumference rings, possibly housed in >2-km tunnels made available by decommissioned high-energy physics accelerators, could have sub-10-pm-rad emittances, providing very high coherence for >10-keV X-rays. A review of fourth-generation ring design concepts and plans in the world is presented.