The MAXIV storage ring project

The MAXIV facility, currently under construction in Lund, Sweden, features two electron storage rings operated at 3GeV and 1.5GeV and optimized for the hard X-ray and soft X-ray/VUV spectral ranges, respectively. A 3GeV linear accelerator serves as a full-energy injector into both rings as well as a driver for a short-pulse facility, in which undulators produce X-ray pulses as short as 100fs. The 3GeV ring employs a multibend achromat (MBA) lattice to achieve, in a relatively short circumference of 528m, a bare lattice emittance of 0.33nmrad, which reduces to 0.2nmrad as insertion devices are added. The engineering implementation of the MBA lattice raises several technological problems. The large number of strong magnets per achromat calls for a compact design featuring small-gap combined-function magnets grouped into cells and sharing a common iron yoke. The small apertures lead to a low-conductance vacuum chamber design that relies on the chamber itself as a distributed copper absorber for the heat deposited by synchrotron radiation, while non-evaporable getter (NEG) coating provides for reduced photodesorption yields and distributed pumping. Finally, a low main frequency (100MHz) is chosen for the RF system yielding long bunches, which are further elongated by passively operated third-harmonic Landau cavities, thus alleviating collective effects, both coherent (e.g. resistive wall instabilities) and incoherent (intrabeam scattering). In this paper, we focus on the MAXIV 3GeV ring and present the lattice design as well as the engineering solutions to the challenges inherent to such a design. As the first realisation of a light source based on the MBA concept, the MAXIV 3GeV ring offers an opportunity for validation of concepts that are likely to be essential ingredients of future diffraction-limited light sources.