2.2 KiB
Operating principle
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.
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.
How to use
- Open photon diagnostics web app
- Under Position/calibration tabs,s elect device from drop down menu 1
- Select target from drop down menu 2 - default target is 50nm Si3N4
- Press calibrate
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.
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.
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.
Error
Soft limits
Error message: ERROR: Motor position outside soft limits
Problem is a soft limit on either the device Motor X or Y is blocking the scan motion
- Select all from drop down menu for motor X and motor Y of PBPS GUI (shown below)
- Change motor soft limits to 1 and -1 for both motors
- Retry calibration