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

1 6 6 H I G H L I G H T S 2 0 2 2 I

RUN NUMBER 2022-01 2022-02 2022-03 2022-04 2022-05 TOTAL 2022

Scheduled beam time (H) 1152 906 1344 1056 1032 5490

Delivery time (H) 1147.7 900.9 1326 1046.6 1017.3 5438.5

Availability 99.63% 99.44% 98.66% 99.11% 98.58% 99.06%

Dead time for failures 0.37% 0.56% 1.34% 0.89% 1.42% 0.94%

Number of failures 7 8 17 11 19 62

Mean time between failures (H) 164.6 113.3 79.1 96 54.3 88.5

Mean duration of a failure (H) 0.61 0.64 1.06 0.85 0.77 0.83

Table 1: Overview of the EBS storage ring operation in 2022.

Summary of accelerator operation

2022 was the first year with a standard operation schedule since the Extremely Brilliant Source (EBS) was commissioned in August 2020.

Two years after commissioning, tireless efforts have been made to continuously improve the EBS reliability, the efforts of which are reflected in the excellent Mean Time Between Failures of 88.5 hours, shown in Table 1. In the same vein, the mean duration of a failure decreased by a factor three (from 2.4 to 0.83 hours), leading to an excellent accelerator availability of 99.06 %.

The longest failure of 2022 was due to sudden damage to an RF cavity coupler, forcing the time-consuming replacement of this device on two occasions. Following thorough analysis, it was discovered that a series of RF interlock thresholds did not stop feeding the cavity with power when voltage breakdowns occurred. After adjustments, no more such failures occurred.

Four repetitive failures, occurring at the same time on consecutive evenings, caused severe disturbance to the electrical mains on the 20 kV line. A thorough investigation revealed that this was due to a change, without warning, in voltage and frequency in the signal sent by the electricity provider (GEG) to trigger a change in the price of electricity at night. This unusual signal distortion was interpreted by our protection system as a voltage frequency drift, which stopped sub-systems, causing beam trips. The electricity provider agreed to restore the original signal, and the issue disappeared.

Besides efforts to continuously increase machine reliability, permanent developments were made to improve beam quality delivery and performance: minimisation of the injection perturbations, implementation of the power supply Hotswap system, new in-vacuum cryogenic undulators and finding advantageous RF working points without changing delivery performance, the goal of which is to make significant reductions in yearly electricity consumption.

Filling modes

During 2022, five different modes were delivered: 7/8 + 1, uniform, 16-bunch, 4-bunch and hybrid 28*12+1. 16-bunch mode was provided with three different intensities: 35 mA, 65 mA and eventually 75 mA.

In December 2021, the remaining limiting factor of EBS came from the overheating of the kicker ceramic chambers, which forced the delivery of the time-structure modes at lower-than-nominal intensities. As a short-term strategy, an extra coating of titanium was added on the four existing chambers to decrease their resistivity, and hence their beam-induced over-heating. This was done in two steps, explaining why 16-bunch mode was delivered first at

35 mA in February 2022 then at 65 mA in May 2022. In parallel, a new design has been created, which will be available in 2023.

With the kicker chambers installed, tests with increased beam intensity up to 75 mA in 16-bunch and open ID gaps were performed in May, keeping the temperature of the kicker chambers at an acceptable level. Yet a new limiting factor appeared: when closing the gaps of the ID15 and ID16 in-vacuum cryogenic undulators to working conditions, pressure increases occurred, mostly due to heating of the RF fingers. As a precautionary measure, the intensity in 16-bunch was limited to 65 mA to allow ID15 and ID16 to work with closed gaps. A new, more robust RF finger design was installed during the summer.