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Operating the beamline

Setting the beam position

Along the beamline there are 3 axes affecting the position of the photon beam:

axis actuation photon beam position scope
prefocusing mirror roll (J1) motorized (by BeamLine or Kleopatra) 1 vertical on the entrance slit maximum intensity passing through the entrance slit
prefocusing mirror pitch (J2) motorized (by BeamLine or Kleopatra) 1 horizontal all along the beamline photon beam horizontally in the center of the exit slit
and in electron analyzer focus 2
refocusing mirror pitch manual (by micrometer) 3 vertical on the sample photon beam vertically in electron analyzer focus
1 Due to mechanical reasons, both axes can be operated directly only in the increasing direction but always with reasonable backlash in the opposite direction. Reasonable means that a change in mesh current can be observed.

Examples:
  • To increase the value of J1 from 0.32 to 0.33 use move j1 0.33.
  • To decrease the value of J1 from 0.33 to 0.32 use move j1 0.28
    and then move j1 0.32.
  • To increase the value of J2 from 1.62 to 1.63 use move j2 1.63.
  • To decrease the value of J2 from 1.63 to 1.62 use move j2 1.4
    and then move j2 1.62.
2 Primarily to the center of the exit slit. The correct focus of the analyzer is then adjusted by x,y sample position during alignment.

3 Micrometer location:


By moving these 3 axes we can compensate for the position variations of the electron beam in the storage ring that can be slightly different after each injection and/or modified by the machine operators on request of other beamlines (mostly SYRMEP with which we share the same photon source).

All other optical elements are aligned the way that the beam position on the sample does not change upon photon energy and resolution setting.

Procedure

  1. Open the beamline (electropneumatic valves 9-1) and let it warm up for at least 30 minutes (preferably 2-4 hours).
  2. Set the photon energy to any value between 100 and 150 eV using Kleopatra software.
  3. Set the mesh current (monitored by Mesh Monitor) to maximum, either by
    • performing an automatic full J1 scan procedure by clicking on AutoRoll button in the Prefocus section of Kleopatra (that will move J1 to 0.29, scan J1 up to 0.45 while observing the mesh current, determine J1max by fitting the 5 experimental points nearest to the maximum, move J1 to J1max-0.1 (backlash) and finally move J1 to J1max; or
    • moving J1 (in 0.002 steps) to reach the maximum mesh current, by using directly the BeamLine software or PrefocusConsole or Kleopatra console in Kleopatra. This procedure is faster for smaller corrections than the full AutoRoll scan if you are not too far from the maximum.
    This procedure ensures you that you are using the highest possible photon beam intensity.
  4. Check the horizontal beam position through the mirror in the downstream viewport near the exit slit which is covered by a luminofor. (There is a 45° mirror near the beam line which permits you to look at the exit slit in the downstream direction.)
  5. You should see a vertical line in the middle of the slit. If it is seen too much on the left side, increase the value of J2 in the BeamLine software or PrefocusConsole or Kleopatra console in Kleopatra. If it is too much on the right side, decrease the value of J2 (use backlash to 1.4). This procedure ensures you that the beam will pass through the focal point of the electron analyzer in horizontal direction.
  6. Proceed with sample alignment with respect to the analyzer and photon beam.
  7. With the intensity timescan in the SpecsLab2 software still running sligtly change the refocusing mirror pitch and check that the intensity is at the maximum or not far. Usually no adjustment is necessary. This procedure ensures you that the beam will pass through the focal point of the electron analyzer in vertical direction.

Last Updated on Wednesday, 28 February 2018 13:58