18 lines
1.7 KiB
Markdown
18 lines
1.7 KiB
Markdown
## Operating principle
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Single shot diagnostic to measure relative pulse energy and beam position. Back-scattered X-rays from a thin target (typically 50 nm silicon nitride) are measured by four photodiodes positioned above, below, left and right of the X-ray beam.
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Position data maintains FEL pointing, while single-shot pulse energy measurements are used to normalise experiment data. There is one PBPS in the front-end and two further devices per end station.
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## How to use
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1. Open photon diagnostics [web app](https://sf-photodiag.psi.ch/app)
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2. Under Position/calibration tabs,s elect device from drop down menu 1
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3. Select target from drop down menu 2 - default target is 50nm Si3N4
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4. Press calibrate
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<img src="https://docs.google.com/drawings/d/e/2PACX-1vRGynTQ54ugugA_bM9pYc9eZDlet3Z9MSZWn17wJNwAEM2ORiJGoL8O61frpLBVRpFKlzJ7M05a5Mb1/pub?w=1245&h=1039">
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The calibration procedure normalizes the response of the 4 diodes, then scans the device horizontally and vertically over the FEL beam to calibrate the position response.
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Once completed (approx 1 minute) the plots are updated with the calibration response. Plotted on the x axis is the device motor position (horizontal - left plot and vertical - right plot) and on the y axis is plotted the normalized horizontal or vertical diode pair response. For a good setup the plot should be a straight line through the 3 data points.
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If you are happy with the calibration, press the "Push results/elog" button where the new calibration data is sent to the required data processing pipelines. After an automated restart (~30 seconds) both PV and BS position and intensity data will be calculated with the new calibration. An elog entry is made detailing the calibration data. |