A C C E L E R A T O R A N D S O U R C E

1 8 2 H I G H L I G H T S 2 0 2 1 I

RUN NUMBER 2021-01 2021-02 2021-03 2021-04 2021-05 TOTAL 2021

Scheduled beam time (hr) 1080 696 792 1048 1032 4648

Delivery time (hr) 1066.6 674.87 778 1027.8 931.3 4478.6

Availability 98.8% 97% 98.2% 98.1% 90.2% 96.4%

Dead time for failures 1.2% 3% 1.8% 1.9% 9.8% 3.6%

Number of failures 6 12 13 21 18 70

Mean time between failures (hr) 180 58 60.9 49.9 57.3 66.4

Mean duration of a failure (hr) 2.23 1.76 1.08 0.96 5.60 2.41

Summary of accelerator operation

The first User Service Mode (USM) year with the new EBS storage ring has been successful, with fruitful scientific outcomes and continuously improving accelerator performances. Despite the third wave of the worldwide COVID-19 pandemic, which forced users to carry out their experiments from home with remote access to the stations of most beamlines, the storage ring was kept tuned and its performances optimised. During Machine- Dedicated Time (MDT), the injection efficiency was gradually enhanced to about 80% by continually optimising the sextupole and octupole strengths, along with other relevant parameters. All of these improvements have gradually resulted in an increase in beam lifetime. In the meantime, the beam emittances in the horizontal and vertical planes remain unchanged at ~120 pm and 10 pm, respectively, in the uniform and 7/8+1 filling patterns of USM operation.

To improve the beam performance, the old fast-ramp power supplies were replaced with newly installed

kicker power supplies, providing a slow increment of power to the injection kickers and reducing the disturbance to the beamlines during the injection period as a result. These will be put into operation fully by the end of the year 2021. Another significant measure to promote the reliability and availability of the accelerator, a HotSwap system for the magnet power supplies to all the quadrupoles, was connected in the normal power supply system this year, and is being tested during routine operation. It aims to make it easier to change any faulty power supply without any impact on the beam operation.

As a result, in 2021, 4478.6 hours of beam were delivered to users out of 4648 scheduled hours, with a beam availability of 96.4%, and a Mean Time Between Failures (MTBF) of 66.4 hours. This is remarkable for a new accelerator after its first year of user operation, and reaches the same level of reliability as the previous machine in the year 2018. The detailed statistics of EBS operation are shown in Table 1.

Table 1: Overview of the EBS storage ring operation in 2021.

Filling modes and top-up

Over the 10 months of operation in 2021, five different modes were delivered: 7/8 + 1, uniform, 28*12, 16-bunch, and 4-bunch mode. Concerning 7/8+1 and uniform modes, all nominal parameters (i.e., an intensity of 200 mA for a lifetime greater than 25 hours with a stabilised vertical emittance of 10 pm.rad), were successfully reached and delivered. However, the initially planned 16-bunch and 4-bunch modes could not be delivered with nominal beam currents in order to protect the ceramic kicker chamber, which was found to be unable to withstand the increased thermal stress.

The temperature increase is a direct consequence of the intensity per bunch and explains why modes with fewer bunches cannot yet be delivered with higher bunch current. The manufacture of new ceramic chambers has been delayed due to technical problems, but the backup option of re-coating the current kicker chamber to reduce the impedance and, as a consequence, lower the temperature of the ceramic chambers, is ongoing with the highest priority. The completion of the installation of new kicker chambers is expected in March 2022. Until then, temporary solutions have been found by delivering 28*12 bunches at 128 mA, 16-bunch at 35 mA and 4-bunch at 20 mA.