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at the corners was three times again what was observed on ID14 (60 µm/°C see Figures 149a and 149b). Due to the layout of the system on BM18, it was possible to study the tilt along and across the slab/beam. Interestingly, the maximum tilt across the beam occurs along the beam axis. Figures 149c and 149d show us that at the beam height (i.e., 1.4 m above the floor), we can see horizontal movements of roughly 70 µm/°C across the beam.
The results from these three studies were inconclusive. Consequently, a long-term study has been initiated with a dense HLS installation on the first two slabs of the BM19 beamline. It is hoped that this study will resolve some of the issues with the ID03, ID14 and BM18 studies, and ultimately provide data for an ESRF slab thermal bending model that can be used in the analysis and eventual design of future ESRF slabs and beamlines.
D. Martin. ESRF. Special thanks to G. Gatta, L. Maleval and B. Perret of the ESRF Survey and Alignment group for their support in these long and often complex experiments.
REFERENCE  D. Martin & E. Bruas, Experimental Validation of the ESRF Upgrade Program Experimental Hall Prototype Slab, International Workshop on Accelerator Alignment, Fermi Lab (2012).
Fig. 149: a-b) Movement dH of BM18 slab 2b for a temperature change of +1°C. dHc-d) Tilt (µrad) along the BM18 axis of slab 2b for a temperature change of +1°C. dy