Upgrade Project of the SOLEIL Accelerator Complex

Abstract

Introduction The synchrotron SOLEIL is the third-generation French synchrotron light source whose accelerators were commissioned in 2006 and have been opened to users since 2008 [1–3]. The facility provides extremely stable and brilliant photon beams to 29 beamlines using cuttingedge experimental techniques to analyze matter down to the atomic scale using a wide range of energy, ten decades from far infrared to hard X-rays. As a research laboratory and a service platform open to all scientific communities, including industry, the SOLEIL upgrade will be at the heart of the challenges of tomorrow by providing its users with a research tool with unparalleled performance in four main areas whose major benefits are indicated in parentheses: advanced material (material engineering, quantum material, information technologies), health (new pathogens, antibiotic resistance), energy/ sustainable development (batteries, catalysis/ green chemistry), and environment (impact of pollutants, global warming) [4]. The SOLEIL II project is currently in the Technical Design Report Phase (TDR). The project is divided into two phases of five years each. Phase 1, “Construction,” includes the realization of the accelerators, the modifications, and the adaptation of a group of beamlines and the related infrastructure. It also incorporates the accelerators’ shutdown (18-month dark period) and the beginning of the storage ring commissioning. Phase 2, “Towards Full Performance,” starts with the continuation of the storage ring commissioning and the first beamlines’ commissioning; it then progresses towards the full performance of the beamlines thanks to the availability of the latest generations of insertion devices (IDs) and state-ofthe-art beamline new components, allowing us to take full advantage of the coherence and the low emittance electron beam. The SOLEIL II project timescales have changed very recently with the shutdown taking place between mid2028 and the beginning of 2030. For its upgrade, the storage ring would be entirely replaced by a new ring using the new Multi-Bend Achromat (MBA) technology [5, 6] host in the same tunnel as today. While maintaining its broad spectrum of photons, the SOLEIL II project aims at maximizing the intensity of coherent photon flux (the highest possible brilliance and transverse coherence), especially for the beamlines working in the soft and tender Xray energy range. The strategy of SOLEIL II is based on the objective to obtain a natural horizontal emittance of less than 100 pm.rad, and to set horizontal and vertical β-functions close to the matching value at each insertion device source point, keeping the beam intensity at its maximum value of 500 mA and the same circumference of 354 m. In order to mitigate the anticipated large Touschek and Intrabeam scattering effects inherent to very low-emittance storage rings [7, 8] and to achieve a beam lifetime compatible with present shielding walls, the bunch length will be increased by a factor of three to four (with the limit of 100 ps FWHM for timing mode filling patterns) using a harmonic Radio-Frequency (RF) system [9, 10]. These objectives should be reached while maintaining the stability (2– 3% of the beam sizes) and reliability presently achieved (99% beam availability, 100-h mean time between failure) and minimizing the operation costs, in particular the wall-plugpower using technical solutions to significantly reduce its carbon footprint.