11HIGHLIGHTS 2020

emittance of 150 pm, an injection efficiency of about 2% and a lifetime of about one hour.

By the end of January 2020, all parameters foreseen to be achieved at the end of the dedicated machine commissioning period on 1 March 2020 were obtained, more than one month ahead of schedule. In particular, top-up operation at 50 mA was established with a lifetime larger than five hours and an injection efficiency above 60%. The beamline restart programme was thus initiated and, on 30 January 2020, all 27 insertion device (ID) beamlines received X-rays for the first time from the EBS storage ring sources (Figure 1). On 26 ID beamlines, the X-ray beam was found within fractions of millimetres with respect to its previous position before the shutdown on 10 December 2018, with the 27th ID beamline receiving the beam in the correct position shortly afterwards. Work continued to steadily improve the machine performances and reliability and, on 28 February, the EBS design current of 200 mA was reached.

From 2 March, with the official start of the beamline restart programme, storage ring commissioning continued in parallel during the night and on machine dedicated time (MDT) days. By 14 March, the EBS storage ring design parameters required to restart operation in USM on 25 August 2020 were reached or exceeded, more than five months ahead of schedule. In particular, these included top-up operation at 200 mA with a lifetime larger than 11 hours and an injection efficiency in excess of 90%.

Fig. 2: ESRF-EBS, the first high-energy, fourth-generation synchrotron light source opened to users on 25 August 2020.

On 25 August, the experimental programme was restarted on schedule, with the EBS opening in USM operation, delivering 200 mA to all available beamlines (Figure 2). Delivery was performed in 7/8 + 1 filling mode with a single bunch at 3.5 mA in the 1/8 gap and a top-up every hour. By 15 September, the design parameter goals targeted to be achieved by the end of 2021 were reached in USM operation. In particular, the Touschek lifetime exceeded the design values, thus allowing the delivery of 200 mA with a vertical emittance of 10 pm and a lifetime in excess of 20 hours.

All foreseen bending magnet sources were successfully installed and commissioned during scheduled shutdowns and interventions. Vacuum conditioning also continued, together with further debugging and tuning of the accelerator settings aimed at further improving the machine performances. In particular, in- vacuum undulator gap limitations due to beam losses were steadily decreased, and finally reached the values for normal operation, compatible with safety requirements and further improving the X-ray beam performances.

Even with improved Ti coating, the injection kicker chambers experienced excessive heating in 16-bunch and 4-bunch operation, therefore limiting operation in timing modes to a maximum current of 32 mA and 16 mA, respectively. In the context of a joint ASD, ISDD and TID high-priority project, new ceramic kicker and shaker chambers are being designed and procured in order to be able to