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Entry  Tue Oct 23 17:30:33 2012, jamie, nic, jenne, raji, manasa, Update, Alignment, Initial attempts to fix IFO alignment 
    Reply  Tue Oct 23 17:41:20 2012, Manasa, Update, Alignment, Power supply at OMC removed 
       Reply  Tue Oct 23 18:21:21 2012, Jenne, Update, Alignment, Power supply at OMC removed 
    Reply  Tue Oct 23 18:12:18 2012, Jenne, Update, Alignment, Tip tilt wires - the truth 
Message ID: 7599     Entry time: Tue Oct 23 17:30:33 2012     Reply to this: 7600   7601
Author: jamie, nic, jenne, raji, manasa 
Type: Update 
Category: Alignment 
Subject: Initial attempts to fix IFO alignment 

We went into the vertex today to see about fixing the alignment.  The in-air access connector is in place, and we took heavy doors off of BS, ITMY, and ETMY chambers.

We started by looking at the pointing from the PZTs.  Manasa and Raji hooked up HV power supplies to the PZTs and set them to the middle of their ranges (75 V).

We installed a target on the BS cage, and new "free standing" targets made special by Steve for the SOSs on ITMY and ETMY.

Using a free-standing aperture target we looked at the beam height before PZT2.  It was a little high, so we adjusted it with PZT1.  Once that was done we looked at the beam height at PR2, and adjusted that height with PZT1.

We then tried to use the hysteresis in PR2 to adjust the beam height at ITMY.  Pushing just a little bit at the top or bottom of PR2 would repoint the beam in pitch.  This sort of works, but it's stupid.  Using this method we got the beam more or less centered vertically at ITMY.

We moved on to ETMY with the idea that we would again use the hysteresis in PR3 to get the vertical pointing to the ETM correct.  This was a good demonstration of just how stupid the tip-tilts really are.  Just touching slightly at the top or bottom or PR3 we could completely change the pointing at ETMY, by mili-radians (~4 cm over 40m).

At this point I cried foul.  This is not an acceptable situation.  Very little stimulation to the tip-tilts can repoint the beam inside the PR cavity.

Steve says that the TT weights, which will attach to the base of the TT mirror mounts and should help keep the mirrors vertical and not hysteretic, are being baked now and should be available tomorrow.  We therefore decided to stop what we were doing today, since we'll have to just redo it all again tomorrow once the weights are installed.


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