STATUS OF THE EBS STATUS OF THE EBS

10 ESRF

The year 2020 witnessed the culmination of over five years of momentous efforts, with the opening of the Extremely Brilliant Source (EBS) in User Service Mode (USM) operation on 25 August 2020, as scheduled. Despite the challenges posed by the COVID-19 pandemic, including a two-month enforced site closure, the storage ring commissioning and the beamline restart programme were completed as planned. Work is progressing well on the new flagship EBS beamlines and further beamline upgrades are also underway.

PROJECT OVERVIEW

2020 marked the sixth year of the ESRF s EBS project to implement a new, fourth- generation lattice for the storage ring, reducing the equilibrium horizontal emittance from 4 nm to about 135 pm and greatly increasing the brilliance and coherence of the X-rays generated.

The first three months of 2020 were dedicated to continuing the storage ring commissioning begun in December 2019, with key milestones such as first X-ray beam, 200 mA of stored beam current and 20 hours lifetime reached ahead of schedule. By mid-March, just days before the two-month ESRF site closure imposed by the French authorities due to the COVID-19 pandemic, the parameters required to restart in USM operation were obtained. Following the gradual reopening of the ESRF site from mid- May to mid-July, with stringent new sanitary conditions implemented to protect the health and safety of staff working on site, it was decided to maintain the date of 25 August for the restart of USM with a maximum number of operational beamlines. Although some changes of plan were inevitably necessary, progress

was made during the summer on the beamline restart programme and on the interventions in the new EBS storage ring during the August shutdown, culminating in the successful return to USM operation as scheduled. This major achievement the timely and within-budget construction and commissioning of the new EBS storage ring and the restart of the experimental programme of the ESRF user community despite the challenging public health context was recognised by the 12th Machine Advisory Committee (MAC) meeting, held remotely in November 2020.

COMPLETION OF THE STORAGE RING COMMISSIONING PHASE

The beginning of 2020 saw the continuation of the EBS commissioning phase, which started on 28 November 2019 with the first circulation of the electron beam in the new storage ring. On this date, electrons were extracted from the booster, and the transfer line between the booster and the storage ring was successfully commissioned within a few hours. The beam was then transported into the storage ring and circulated for two and a half turns, officially starting the beam commissioning phase. On 6 December 2019, following a few days of characterisation of the circulating beam, the radio frequency (RF) system was switched on and the electron beam was stored. The first stored beam current was about 5-10 μA, with a lifetime of a few minutes. A week later, after further debugging of the subsystems and machine tuning, it was possible to accumulate the beam. At this time, the injection efficiency was about 0.8% and the maximum accumulated current about 0.6 mA. By the end of December 2019, teams were able to store 6.5 mA of beam current, with a world-record horizontal

Fig. 1: Beamlines saw the first EBS X-ray beams in January 2020. The beam shape was almost cylindrical as expected, with submillimetre size at 100 m from the source.