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Entry  Sat Nov 6 07:26:54 2010, yuta, Summary, IOO, reduced common mode displacement of the beam through MC1 to MC3 A2LMCalign.png
    Reply  Tue Nov 9 05:40:12 2010, yuta, Summary, IOO, MC aligning going on MCalignNov9.png
       Reply  Wed Nov 10 02:51:35 2010, yuta, Summary, IOO, limitation of current MC aligning MCalignNov9.png
          Reply  Wed Nov 10 11:46:19 2010, Koji, Summary, IOO, limitation of current MC aligning 
             Reply  Wed Nov 10 12:21:18 2010, yuta, Summary, IOO, limitation of current MC aligning 
                Reply  Wed Nov 10 14:28:33 2010, Koji, Summary, IOO, limitation of current MC aligning 
Message ID: 3876     Entry time: Sat Nov 6 07:26:54 2010     Reply to this: 3883
Author: yuta 
Type: Summary 
Category: IOO 
Subject: reduced common mode displacement of the beam through MC1 to MC3 

(Koji, Suresh, Yuta)

Summary:

  We need MC to be locked and aligned well to align other in-vac optics.
  By using a new python script A2L.py(see elog #3863), we are measuring A2L coupling and centering the beam.
  Tonight's goal was to reduce common mode displacement of the beam through MC1 to MC3, and we succeeded.

Strategy of beam centering:

  We first ignore the beam position at MC2 and focus on MC1,MC3. If MC1,MC3 alignments are given, MC2 alignment is determined.

  For MC1 and MC3, we first reduce the common mode displacement using the last steering mirror at PSL table.
  The last steering mirror makes translation of the incident beam because it is far (~m) from the MC.
  So,
    1. Rotate the steering mirror nob a little
    2. Lock MC so that MC beam axis will be the same as the incident beam axis
    3. A2L measurement
    4. To 1-3 over until the beam crosses MC1 center to MC3 center axis
        The amount of vertical/horizontal displacements of the beam spot at MC1 and MC3 should be the same.
        From our convention, for vertical, MC1 and MC3 should have opposite sign. For horizontal, same sign. (see picture below)

Result:
A2LMCalign.png
 
  From the A2L measurement, now the beam spot is lower right at MC1 and upper right at MC3.
 

  The directions of the beam spot motion agree with the steering mirror tilts.
  Also, the amount of the motion seems reasonable.
    1 tooth rotation of the steering mirror nob makes ~1e-3 inch push which equals to ~0.5mrad rotation.
    The steering mirror to MC is like ~2m and 0.5mrad mirror tilt makes ~2mm displacement at the MC optics.
    2mm displacement is ~15% at the mirror (see Koji's elog #2863;note that coil-coil distance is 1/sqrt(2) of the mirror diameter).
    The measured vertical spot motion is ~15%/1tooth. Horizontal is sqrt(2) times bigger because of the angle of the MC1, MC3 and they are about that much, too.

Plan:
 - Use IM1 to make beam tilt and finally center the beam
 - Improve the script so that it features weighting in fitting
 - Write a script that balances actuation efficiency of the 4 coils.
     We are currently assuming that 4 coils are well balanced.
     In order to do the balancing, we need to balance OSEMs too.

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