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Advanced Photon Source
Sector 9

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Checking Orbit on 9-ID

0.0 General

“Checking the orbit” is synonymous with checking the position of the x-ray beam incident on the 9-ID beamline with respect to its entrance mask FM103.

The procedure of determining the beam position consists of viewing the outline of FM103 on Flag1 with x-rays while tuning and detuning the undulator energy with respect to the monochromator energy.  When the undulator is detuned its 4 lobes of radiation should be visible symetrically in the 4 corners of FM103, on approaching the monochromator energy the 4 lobes should converge in the center of FM103.

In case of a substantial deviation of the actual beam position from its intended position, the APS control room needs to be contacted through the floor coordinator with a request for an appropriate orbit correction.

The entrance mask FM103 is located at 26297 mm (nom.) from the undulator source, in the upstream section of 9-ID A (FOE), immediately downstream of the differential pump. Although it is mounted on a x-y motion stage, its position is kept fixed and centered on the fixed mask FM102, located in the middle of the differential pump.

FM103 provides a square aperture of size 2.1 x 2.1 mm2 with truly sharp corners.

1.0 Procedure

With 9-ID A searched and secured:

  • Open the undulator (gap ~ 45 mm)
  • Open the Front-End Shutter
  • Lower Flag1 into the beam (~ -26 mm or lower) and observe it on the “Flag1” monitor

[Flags] > [Flag #1]      or      [Motors FOE] > [17-24] > [Flag 1]

  • Open the White Beam Slit to 2.1 x 2.1 mm2 (Yu/s = 0.9 mm, Yd/s = -1.0 mm, Xu/s = -2.1 mm, Xd/s = 0.9 mm)
[FM-WBS] > [WBS]
  • Close undulator in small increments (5 mm) and observe convergence of beam within outline of fixed mask
  • If center of intensity distribution is not in the center of the mask request orbit correction: call 2-0101, request correction in increments >= 5 urad
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