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Today, after more than three years of operation of the ESRF s new Extremely Brilliant Source (EBS) storage ring and beamlines, the following observations can be clearly made: first, the Hybrid Multi Bend Achromat (HMBA), the storage ring lattice design invented by Pantaleo Raimondi at the ESRF, is delivering up to the most optimistic expectations. It combines ultra-stable operation even beyond that of the previous third- generation sources with a brightness 100 times higher at the ESRF and up to 1000 times higher in the even more aggressive HMBA designs under development at other synchrotron radiation facilities. It marks the capacity to overcome many of the limitations of the Chasman-Green-based MBA lattice, opening a new era in synchrotron science and applications.

Secondly, the EBS storage ring has delivered according to its design an overall reduction in energy consumption of ~25%: better than planned in 2013 and considerably less expensive to run, given the present energy crisis. Thirdly, the strategies and technologies chosen for the construction and assembly show it is possible to create a ~1 km-circumference storage ring with an increased number of highly complex components aligned to an overall precision of less than 50 μm, and confirm new concepts in magnet design combining magnetic functions (dipole, quadrupoles, gradients, etc.) and managing non- linear effects according to simulations and predictions. Finally, the new beamlines adapted to best exploit the EBS capabilities are performing extremely well, with deliverables that surpass our highest hopes in terms of focusing capabilities, high-energy X-ray beams, coherence exploitation and much more.

At the same time, some issues such as residual beam perturbation at injection need to be optimised, and further possibilities to increase X-ray beam performance

and operation reliability need to be studied and implemented. These include higher harmonic RF cavities for bunch lengthening and lifetime increase, mini-beta optics on selected beamlines enabling a new generation of mini-gap undulators for further brightness increases, and advanced undulator concepts to create combined beam capabilities not available today, such as polarisation plane rotations, etc.

This 2023 edition of the ESRF Highlights showcases an increasing amount of science carried out with EBS and is the most exciting example of the growing interest of the scientific community in using EBS for their research. Indeed, 1075 proposals were submitted for the 2024/I period, up by 120 compared to the 2023/I period. Other indicators include a new European Research Council (ERC) grant awarded to an ESRF scientist on a project that will exploit the new X-ray diffraction microscope under commissioning on ID03 bringing the number of ERC projects hosted at the ESRF up to 10 as well as the success of the new access modes, which are increasing awareness of the new capabilities provided by EBS for cultural heritage, materials science, energy and health research. The Human Organ Atlas programme is a great example of the innovative science now possible with EBS, providing a new standard in biomedical analyses of human organs with unprecedented medical insight and new potential therapeutic applications.

2024 marks 30 years of ESRF operation in User Service Mode (USM) first user experiments began back in 1994! Back then, the ESRF made history as the first third-generation synchrotron, providing an outstanding contribution to science in Europe and beyond, and building a strong community of users. Now, with EBS, the first high-energy, fourth-generation synchrotron light source, the ESRF is once again opening new vistas for

D E A R E S R F U S E R , D E A R R E A D E R