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Figure 6
(a) Beam intensity at the sample position through the 20 µm-diameter aperture with the focused beam (black) and 50 µm-diameter aperture with a defocused beam (red) (FWHM size around 40 µm × 60 µm, horizontal × vertical). The RMS intensity variation is 0.7% and 0.4%, respectively. Measurements made with both optics feedback loops in operation. Data collected at 5 Hz using the diode mounted on the detector cover. (b) Position measured at 200 Hz using the XBPM in the BCU with the feedback loop to the KB mirrors turned off. The BPM is about 0.5 m upstream of the sample position but 4.5 m downstream of the mirrors giving a good measure of the beam stability at the sample position. The vertical position is offset by 2 µm in the figure for clarity. The measured RMS deviation from the mean is about 0.2 µm in both horizontal and vertical direction. The beam without feedback is not always this stable on the seconds time scale, which is the reason for the mirror feedback loop giving the long-term stability shown in (a).

Journal logoJOURNAL OF
SYNCHROTRON
RADIATION
ISSN: 1600-5775
Volume 27| Part 5| September 2020| Pages 1415-1429
https://doi.org/10.1107/S1600577520008723
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