Initial alignment

Before the beamtime starts, the theoretical position of the crystal can be calculated. A finer alignment can then be performed using the reference laser.

During the beamtime, the alignment with X-rays is usually performed using a foil. The concentration of eg. Mn or Fe is higher in the foil, increasing the emission signal and making the alignment significantly easier.

Spectrometer motor overview

An overview of the different motors of the spectrometer and how the different motors move the crystal can be found in on this page: 5.1.2 Six-Element Multicolor XES von Hamos Spectrometer


Setting up AMI screens

  1. Open the ePix100 AMI screen
    1. DAQ Online Monitoring → Data → ePix100_1/ePix100_2
  2. Average the signal over 30 events
    1. Select channel B, then select Averaged → over 30 Events
    2. Unselect channel A
  3. Start a Hit Finder AMI screen
  4. Average the signal in the Hit Finder screen over 30 Events (similar to step 2). Zoom in the window, until the range is from 0 to <1.
  5. Make an X / Y Selection and project the summed intensity of the emission line
    1. In the Image Projection screen that comes up, select "Grab" to make the X / Y selection
    2. Select the "Projection" tab
    3. If you are focusing the emission signal, project sum onto X axis, then select "Plot"
    4. If you are aligning emission signals coming from different crystals, project sum onto Y axis, then select "Plot"
  6. To compare signals before and after you move the crystal, it is helpful to have a reference.
    1. In the Projection screen, select "Reference" (found under "Plot"), then select "Set"


Aligning the von Hamos spectrometer

  1. Open the von Hamos PyDM screen

  2. Focus the emission line using translation until you see them on the detector
    1. 0.5 mm steps
    2. If you can't find the emission line, you can try changing the yaw
  3. Separate the emission lines by changing the yaw
    1. 0.01 degree steps
    2. Tip: write down which emission line corresponds to which crystal before you continue with the alignment
  4. Change the tilt until you captured the full emission line
    1. 0.5 degree steps
  5. Project the summed intensity in X for a crystal at the Y position of choice. Change the translation until the emission line is in focus. Set a reference in the projection.
  6. Move out the crystal from step 5. Move another crystal into the exact position the previous crystal was in and focus using the translation. Make sure the emission aligns with the reference.
  7. Repeat step 6.
  8. Then overlap the emission lines. Plot the intensity on Y. Change the yaw for all crystals until the intensity is maximized.


Troubleshooting

  • The emission intensity does not form a nice Gaussian peak. → The pitch might be off. Change the yaw of the crystal, and check the pitch, one by one.


Old motor names

X → translation

rot → yaw

tilt → pitch