It is absolutely impossible to make all 40 LCLS undulators identical due to variation in the magnet properties and a tolerance stack-up, determining the actual pole gap.

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BASICS

• It is absolutely impossible to make all 40 LCLS
  undulators identical due to variation in the
  magnet properties and a tolerance stack-up,
  determining the actual pole gap.
• Our goal is to find during the magnetic tuning
  for each individual undulator the proper beam
  trajectory coordinates (X and Y) for the same
  K-value.
• Each undulator should be tuned in such a way that
  beam trajectory should be on the intersection of
  the horizontal and vertical planes.
• X and Y coordinates have to be connected to the
  fiducials for each individual undulator through
  the magnetic needles.
  

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How to replace any of the LCLS undulators

• We are expecting that the variations in x
  coordinates between the different LCLS undulators
  will be within 800 1000 microns and the
  variation in Y coordinate will be within 30 50
  microns.
• Undulator supporting plates (on each side) have
  vertical and horizontal shims with the sufficient
  thickness to accommodate X and Y coordinate
  variations by grinding.
• These shims should be precisely ground to get
  dimensions A and B exactly the same for all
  undulators with the precision 20 30 microns for
  the dimension B and 50 70 microns for the
  dimension A.
• A true kinematic mount is not appropriate in my
  opinion . It will decrease rigidity of the whole
  structure without any benefit.

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HOW TO MAKE ALL LCLS UNDULATORS IDENTICAL
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SUPPORT ADJUSTING SHIMS EXPLODED VIEW
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SUPPORT ADJUSTING SHIMS
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CONCLUSION

• Test of the LCLS undulator replacement will be a
  part of SUT.
• We intend to remove the dummy undulator off the
  girder and bring it back 5-6 times and verify
  optically and with the use of KEYENCE non-contact
  laser measurement the precision and repeatability
  of replacement.