We have had trouble with alingment since maintence day today. There were several things that happened that could potentially impact alingment: SUS models were restarted, HEPI work, and adding picomotors to the PSL before the PMC. The PSL work is probably the most likely culprit. I hope that we will be more selective about what we choose to do on maintence day from now on.
Alingment symptoms:
The PMC alingment is not as good as it had been. There were also shifts in the alingments of MC1+3, especially in yaw. Were these from model reboots or did someone intentiaonally change them to relock the mode cleaner? The spot on IM4 trans move from 0.2 in yaw to -0.35 or so. TJ and I trended all the IM osems and they hadn't moved much, but we restored the small changes. Once Jeff B and I finally got the IFO locked (I engaged the soft loops one at a time by hand), our recycling gain was very low (below 24). I tried to move MC1+3 in yaw to restore the position on IM4, both earlier with TJ and with the full IFO locked, the MC WFS generally drag it back to where it was. With the full IFO locked I moved IM3 in yaw, which did help the recycling gain (I chose IM3 because it's after teh Faraday, not because I think it is what moved). I moved it too fast and broke the interferometer lock, so we finished using it to restore the position on IM4 Trans with just the mode cleaner locked. We partially reverted this because we saw no flashes in the arm, and are going to give up for the night now.
If we still have this problem in the morning, it is probably worth taking a look at the irises that Cheryl placed on the PSL table a while ago to see if the beam goes into the IMC with the same alignment.
REFL WFS don't work for PR2 at 2 Watts:
I changed the ISC_LOCK guardian back to using POPX WFS for acquisition. The point of the POPX WFS is that they can be used even when inital alingment isn't great and the recycling gain is low, so we would like to keep them on for power up and switch to REFL WFS in LOWNOISE_ASC. I've put some code in low noise ASC to switch back, but we haven't gotten to test this yet. I guess that the matrix to use REFL to control PR2 was probably tested at 25 Watts last night but set up in the guardian for use at 2 Watts, because Jeff B couldn't engage the REFL WFS yesterday morning after commisioners left. Tonight it was clearly breaking the lock, which might have been partly because of our bad alingment, but when we changed it back to POPX it was fine.
Initial Alignment changes:
Jeff B and I just made a few changes to initial alingment, after TJ, Evan, and I had difficulty with input align earlier in the night. Although our alingment change today probably contributed to this, I think the changes are good and things I've been meaning to do for a while anyway.
- We re wrote the REFL WFS Centering states to be identical to the WFS centering states used in DRMI, without the AS loops. This was beacsue the old refl wfs centering state would not always stop the operator from continuing to align if the DC servos were railed.
- We changed the INPUT align state from using REFL WFS, which have very little light on them but were the only WFS available when we first wrote this state, to using AS45I. These are better signals and I've been meaning to make the change for a while now. To do this we made AS WFS centering states which are a copy of the REFL WFS centering states.
Betsy, Jason, Travis, Kiwamu,
After some investigation and tentative adjustments, the situation did not improve after all. We still have no idea what happened.
In the end, we restored all the suspensions back to where they were before the maintenance and steered the IM3 yaw to obtain a value of +0.2 in IM4_TRANS_YAW.
[Some conclusions]
[Summary of the activities]
[Summary of the shift]
The following tables summarize the alignment before the alignment and after our investigation and adjustments.
Summary table for pitch
before [urad]
around Oct/24/2016 20:50 UTC
after [urad]
around Oct/26/2016 21:20 UTC
change [urad]
after - before
Summary table for yaw
before [urad]
around Oct/24/2016 20:50 UTC
after [urad]
around Oct/26/2016 21:20 UTC
change [urad]
after - before
As I was writing these values, I noticed that the the beam waist location of the IMC translated by roughly 0.5 mm according to equation (4) in P1000135. I have no idea how we ended up introducing this translation in the IMC eigen axis without changing the input beam line determined by the PSL periscope mirror and the MC2 spot position. As expected, we compensated whatever the misalignment by introducing a +182 urad offset to IM2. If this compensation by IM3 is not perfect (and probably this is true in reality), this will result in a different spot position on PRM. The rest of the interferometer should be fine in principle.
Jenne, Sheila, Kiwamu,
In addition, we did a brief test in order to distinguish whether this is due to a change in the PLS pointing or something in the suspensions.
We conclude that misalignment in PSL (if any) don't explain what we see on IM4_TRANS. Again, we still don't have an idea of what happened.
[The test]
We restored all the suspensions back to the values listed above. We disabled the IMC ASCs so that they don't pull the suspensions to whatever the points they want to park. The idea is that with the restored suspension, we should get back to the same value on IM4_TRANS if all the misalignment was due to something in the PSL. If the spot on IM4_TRANS does not come back to the old location, then something in the chamber must have changed.
[Results]
Initially, the yaw signal of IM4_TRANS was about -0.4 counts before we restored the suspensions. After the restoration, the value became -0.1 which is closer to what it was (+0.2). However, obviously we did not fully come back to the old value on IM4_TRANS. This means that misalignment in PSL alone can not explain the situation right now. Something else likely in the chamber must have moved.
This result motivated us not to touch the PSL. Instead we decided to move IMs to recover a high recycling gain in the interferometer (30910).