To calibrate the XRT spectrometer (formerly known as the FEE spectrometer), we do a notch scan. By changing the XPP monochromator energy in small steps, we can see the notch changing in the spectrometer readout.

Perform a notch scan every time the XRT spectrometer has changed position (when it has been used for different X-ray energies for example).

Notch scans should be performed only at the start of the first shift or after an energy change! The diamond crystal angle does not come back to the original position, which can cause issues for XPP.


Recording calibration data

  1. If you are multiplexing with XPP, make sure to call XPP to ask if you can change the mono energy for the next few minutes.
  2. Check the XRT spectrometer camera (camViewer -c fee_spec)


    If needed, move the camera Y position, so the spectrum is centered on the camera (the XRT HXSS Spectrometer window to do this can be found in mfxhome, under the tab "LCLS").
  3. If the center spectrum is not on the center, move the camera angle(0.1deg step)
  4. Make sure the spectrometer data is being collected by the DAQ (selecting the partition "FEE_SPEC0" in the DAQ). Open up the AMI screen.

  5. Start xpppython (you can also use xpp3)

    ssh xpp-monitor
cd ~xppopr/bin
./xpppython

  6. Move in the monochromator and check the energy the XPP monochromator is currently set to in xpppython

    lom.h1n.mv(0) # the value of 0 is first crystal "in" and -10 is first crystal "out"
lom.E1C.wm()
  7. Record the spectrum for 1 minute using the DAQ.

  8. Change the XPP monochromator using 10 eV steps. It is recommended to record the position at the intended X-ray energy for the experiment, +5 eV, +10 eV, -5 eV and -10 eV. For example:

    lom.th1C(BraggAngle('C*',(1,1,1),9.41))

    Never move EC or E1C ! Only move th1C!


    Record another 1 minute run every time you move the monochromator.

    AMI feedback

    Set a reference in the AMI screen, to ensure the notch is moving:

    Ensure that the notch remains within the X-ray spectrum:



  9. Move back th1 to the intended energy. Inform XPP you are finished with the calibration, in case you are multiplexing.


Analysis of the XRT spectrum

Aaron Brewster from LBL plotted the notch position as a function of XPP mono energy calibration for 8.8 keV.


The spectrometer was camera was re-aligned midway through the experiment to enable Aaron make use of the low energy portion of the spectrum.


The effect of changing the camera tilt was to increase the spread of the spectrum on the the spectrometer from 0.0337 eV/pixel to 0.0341 ev/pixel. The difference amounts to 0.8 eV over 2000 pixels but the increased access to the full spectrum is considered more important to Aaron.

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