This is a very special time for the beamlines of the Matter at Extremes group and, in general, for the ESRF as a whole. With the successful commissioning of the Extremely Brilliant Source (EBS) and the first results showing exceptional performance, a period of excitement and effervescence begins. The new X-ray source will allow the realisation of experiments beyond the capacities of the former machine. In particular, experiments under extreme static and dynamic pressure conditions, which are very demanding in terms of photon flux, will enter into a new paradigm. In addition to the high X-ray beam quality brought about by the EBS, and despite the difficulties related to the COVID-19 pandemic, a major plan to rejuvenate and improve the Matter at Extremes group s beamlines is well underway to offer a high- level instrumental environment for users and in-house research experiments.

State-of-the art detector systems are currently deployed at the three X-ray diffraction (XRD) beamlines ID06LVP, ID15B and ID27. At ID6LVP, a Pilatus2 CdTe device is now interfaced to the large volume press. The system has been in user operation since August 2020 and, combined with the EBS beam, can offer unprecedented diffraction quality of data collected under extreme conditions of pressure and temperature. ID15B is another big winner of the EBS upgrade as the maximum intensity has increased by a factor of 16 to reach ~1013 photons/sec. This, coupled with an improved beam-focusing scheme and an Eiger2 9M detector, will provide enhanced capabilities for the efficient collection of high-quality XRD data.

ID18, the nuclear resonance beamline, will offer the user community two outstanding new devices: the nanoscope and spectrograph. Both instruments will be optimised for the most demanded 57Fe nuclear resonance, i.e., with X-ray energy of 14.4125 keV. The nanoscope will considerably improve the spatial resolution from ~10 µm to submicron X-ray beam size without compromising the photon flux. This small beam size will be available for hyperfine spectroscopy both in the time domain (nuclear forward scattering) and the energy domain (synchrotron Mössbauer source), and for lattice dynamics (nuclear inelastic scattering). The spectrograph will drastically improve the energy resolution from ~0.6 meV to ~100 µeV while keeping nearly the same beam intensity. The refurbishment programme on the two X-ray absorption spectroscopy (XAS) beamlines BM23 and ID24

is progressing very well. The extended X-ray absorption fine structure (EXAFS) instrument BM23 will be back to full user operation in January 2021 as initially planned. The new two-pole wiggler X-ray source is functioning well and provides a gain of a factor three in intensity and a reduction by a factor two of the focused beam size. The new micro-XAS station on BM23 will enable high-pressure experiments using more complex sample environments (e.g., multi-megabar diamond anvil cells (DACs), resistively heated and cryogenically cooled DACs) and highly diluted and heterogeneous samples. In addition, combined XAS and XRD studies will be possible using a newly installed Pilatus 1M detector. The refurbishment of ID24 consists of the conversion of the energy- dispersive XAS (EDXAS-S) branch into a high- brilliance XAS beamline equipped with a high- precision double-crystal monochromator (DCM). This instrument will be fully optimised for in-situ and operando chemistry and high- pressure/temperature studies. Coupled to a five-crystal analyser spectrometer, it will enable state-of-the-art micro-XAS analysis. The opening of the ID24-DCM branch is planned for March 2022. The second branch, ID24-ED, will provide time-resolved XAS capabilities down to 100-picosecond time resolution. It will be mainly devoted to studies under high-pulsed magnetic field and dynamic compression using the High Power Laser Facility (HPLF) platform that is currently under construction. The ID24- ED beamline and HPLF platform will host its first users in September 2021.

Finally, a major refurbishment is ongoing at the high-pressure XRD beamline ID27. The construction of the main beamline infrastructure on the high-stability slab of the ESRF Chartreuse Hall has started, and will be finalised in July 2021. This instrument will provide nano- focusing monochromatic and pink beam capabilities and a gain in intensity of up to three orders of magnitude. It will be optimised for in- situ XRD but good quality in-situ X-ray imaging and X-ray fluorescence will also be available. As initially planned, ID27 will re-open to users in November 2021.

The selection of work presented in this chapter mostly results from data collected pre-EBS. It includes high-quality, in-house and user research examples from a diversity of scientific fields. It features three contributions from the Earth and environmental sciences: at ID18, J.P. Perez et al. have performed nanoscale mapping of arsenic binding on green rust (page 20). The green rust

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