173HIGHLIGHTS 2020

D. Martin. ESRF AUTHOR

Uncertainties of magnet positions U(dR) and U(dZ) for these three surveys were less than 40 µm, even after transportation. In other words, it is clear that there are negligible movements of the magnets on the girders. Therefore, any significant movement would be expected between adjacent girder assemblies.

Table 1 provides summary values of movements between adjacent girders (ddR and ddZ), between the final alignment in November 2019, and July 2020 and October 2020. In the previous machine, maximum movements between adjacent girders, mainly dZ, were roughly 300 µm. These movements were observed between the winter and summer shutdowns and driven by the annual temperature cycle. With the new machine, the observed movements are an order of magnitude smaller. They are particularly small in the sensitive zone across the high-focusing quadrupoles and combined- function dipoles in the centre of the cell between the G2 girder, DQ2 assembly and G3 girder.

In the previous machine, there were large vertical movements between the summer and winter observed at the entrance of the G20 girder. Therefore, it is interesting to know if there is any systematic movement similar to what was observed previously. The mean annual

movement cycle dR and dZ for the 32 EBS storage ring cells, at least for the first year of EBS, are shown in Figures 147a and b. Although there appears to be systematic movement both in R and in Z, the movements are very small. With judicious engineering, these movements have been largely attenuated in the new EBS machine. There are negligible movements of the magnets on the girders, so any significant movement would be expected to occur between adjacent girders. Survey and Alignment group observations between November 2019, and July and October 2020 show these movements are much smaller than in the previous machine and, specifically, movements across the alignment- sensitive high-focusing and combined-function dipole magnets in the centre of the cell are reassuringly small.

November 2019 to July 2020 to October 2020 ddR ddZ ddR ddZ G1 to G2 34 26 47 30 G2 to DQ2 assembly 32 21 35 25 DQ2 assembly to G3 33 22 35 29 G3 to G4 50 47 50 48

Table 1: Mean movements between girders for the 32 storage ring cells from November 2019 to July 2020 and to October 2020.

Fig. 147: Evolution of the girders between November 2019 and July 2020. a) dR, b) dZ.

EBS VACUUM CONDITIONING Most of 2020 has been dedicated to commissioning the new EBS storage ring. Many devices and technologies are necessary for a fully operating machine and, among these, good vacuum is essential for attaining full beam performance. The vacuum system has met and surpassed its design goals, and the key milestone of user operation has been achieved on schedule.

In the design of the new EBS storage ring, vacuum performance was considered one of the key parameters. The lower the vacuum level,

the lower the interaction between the electron beam and residual gas. Consequently, electron and X-ray beam quality is higher; beam losses