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Figure 8
After removing the constant pitch of −0.6 µrad from the tangential-plane height-error curves plotted in Fig. 5[link] and zooming in to the central ±70 mm of the mirror, the thermoelastic distortion of the mirror for cool-down from 295 to 77 K (cold) and a range of undulator K values can be more easily compared. Because of the thermal tuning of the mirror system, the mirror temperature is entirely in the negative CTE regime for silicon up to K = 2.75 and is therefore concave. At K = 2.75 the maximum temperature crosses 125 K, which can be seen by the small convex bump at x ≃ 40 mm. At K = 3 the mirror temperature has increased and the central portion of the mirror begins to flatten. The curves are given for the linear horizontal polarization mode of the undulator.

Journal logoJOURNAL OF
SYNCHROTRON
RADIATION
ISSN: 1600-5775
Volume 27| Part 5| September 2020| Pages 1131-1140
https://doi.org/10.1107/S1600577520008930
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