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Measured energy calibrations disagree wildly:
| Energy Calibration | Elog Entry |
|---|---|
| 43.9 keV/um | http://physics-elog.slac.stanford.edu/facetelog/show.jsp?dir=/2024/10/08.03&pos=2024-03-08T10:52:50 |
| 54.7 keV/um (41.7-64.2 keV/um measured) | http://physics-elog.slac.stanford.edu/facetelog/show.jsp?dir=/2024/10/08.03&pos=2024-03-08T10:52:50 |
| 20.0-50.8 keV/um | http://physics-elog.slac.stanford.edu/facetelog/show.jsp?dir=/2024/25/18.06&pos=2024-06-18T05:44:40 |
The design dispersion at the screen is 111.7mm which means the calibration should be 10.0 GeV / 111.7 mm = 89.5 keV/um. The difference between the measured and expected could be due to the screen calibration. No calibration images ever appear in the elog. The calibration starts at 17.94 um/px when the camera first appears on one of the FACET-II camera server. The calibration then changes to 9.91 um/px starting with this elog entry, but no calibration images appear in the e-log, this value as been used for all of FACET-II. The value matches the value used at FACET, most likely the old FACET value was used without every taking a new calibration.
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The two devices are separated by a quadrupole that focuses in x, resulting in the nearly identical dispersion at the two devices. SYAG is located right before the last positive dispersion peak and BPM 2445 is located right after the dispersion peak.
From particle tracking, the expected beam profiles at the two screens are shown below. Based off these images, the beam should have an energy spread of +-0.05 GeV spread over about 1 mm which would give an energy calibration of ~100 keV/um, which agrees with the calibration expected from the nominal dispersion.
| SYAG | BPM 2445 |
|---|---|
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In Doug's, the SYAG spectrum is compared to the spectrum on DTOTR1 and the results agree, qualitatively:
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