EBS STORAGE RING ALIGNMENT ONE YEAR ON ENABLING TECHNOLOGIES

172 ESRF

Alignment played a key role in the successful machine and beamline commissioning of the new ESRF-EBS machine. Alignment tolerance for the most critical magnets is 60 µm in the two directions perpendicular to the travel of the beam. These tolerances were successfully achieved in November 2019. However, what is the alignment status of the machine today, and how can we anticipate its evolution over time?

The final alignment of the ESRF-EBS storage ring was completed over two weeks in November 2019. This work involved positioning the girders onto a trajectory that respected the source point positions and beamline directions of the previous machine, while maintaining the alignment tolerances between magnets on adjacent girder (G) assemblies (i.e., G1 to G2, G2 to the DQ2 magnet assembly installed across the end of G2 to the beginning of G3, and G3 to G4).

As with the previous storage ring, the new EBS machine is not in its nominal position, due to constraints for following the previous machine s trajectory. The storage ring has assumed a position imposed by local geography and ground movements over the past 30 years. This current form (i.e., the new EBS machine in November 2019) is shown in Figure 146a (dR: horizontal direction perpendicular to the beam) and Figure 146c (dZ: vertical direction perpendicular to the beam travel). Residuals with respect to the smooth curves modelling the form of the machine are shown in Figure 146b (dR) and Figure 146d (dZ). Residuals with respect

to these smooth curves are indicative of the quality of the machine alignment. The alignment uncertainties for the EBS storage ring in November 2019, U(dR) and U(dZ), were 53 µm and 30 µm respectively.

These are impressive results, but a key question is how much has the machine moved over the past year? It is important to know, as the previous storage ring had large annual vertical movements in the order of 300 µm. These movements were a result of slab bending that is driven by temperature gradient variations through the slab. Similar cycles in the new machine would far exceed the acceptable alignment tolerances.

The ESRF s Survey and Alignment group has followed the evolution of the machine alignment regularly since November 2019 at least, as regularly as the COVID-19 pandemic situation permitted. Surveys were carried out in January, February, July and October. Three comprehensive surveys of the girder were made during assembly and installation in the tunnel.

Fig. 146: a) Final alignment dR of the storage ring.

b) dR residuals with respect to a

smooth curve. c) Final dZ

alignment of the machine.

d) dZ residuals with respect to a

smooth curve.