douglas.cook@LIGO.ORG - posted 15:47, Thursday 19 January 2012 - last comment - 16:40, Thursday 19 January 2012(2069)
H2 ITMy suspension initial alignment and the ACB centering
(Doug, Travis, Hugh, Annamaria, Jason)
The final pointing is PITCH ~ 9uradians to the required beam line
Yaw ~ 10 uradians to the required beam line
Having the Cartridge alignments and the GAP/parallel alignments accuracies close was very useful as the laser collimator return reflection was swinging through when the optic was released from the EQ stops.
Tightening the setscrews on the pitch adjuster screws influenced the pitch pointing by ~ 150 uradians.
Care must be taken to determine the HR reflection from the AR reflection.
One full turn of the sus pitch adjuster = about 400urads of pitch change.
1/4 turn of the static ISI adjusters = about 240 urads. This was done by tightening one sid and loosening the opposite and working through the 8 adjusters.
The arm cavity baffle alignment visually as seen through the theodolite is well centered. The baffle apurature is not perfectly round and so I averaged the gap about the ITMy. Previous measurements from the corner cube gave us a quantitative number for its location. The pusher assembly needs to be removed yet.
In the end all went well, but patience is needed and damping ring down takes 15 minutes or so to see the readout.
Just a clarification of Doug's statement that "One full turn of the sus pitch adjuster = about 400urads of pitch change.". This is a result of a measurement taken by Jason (he might be able to give a more accurate figure, but this is what stuck in my head, and either way, is just a approximate figure for use by those tuning the suspensions) on ITMy during coarse pitch adjustment after welding. A more accurate statement would be "One full turn of both pitch adjusters on the UIM yield about 400 uradians of pitch". We have not used the Top Mass fine pitch adjusters for much of the real "fine" pitch due to the fact that the upper one is inaccessible once the tablecloth for the OSEMs is installed. Perhaps we should consider modifying the tablecloth plates to allow access to these adjusters (specifically the top one) as using only the UIM stage adjusters may be less than ideal (those with Matlab/Mathematica mastery could speak to this better).