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Reports until 21:14, Tuesday 27 September 2016
H1 ISC
stefan.ballmer@LIGO.ORG - posted 21:14, Tuesday 27 September 2016 - last comment - 06:23, Wednesday 28 September 2016(30030)
Some noise chasing

 

- The DCPDs whitening chassis was found to be switched to Low-Z - transitioned back to high-Z.

- We added notch filters for the 4.01Hz and5.01Hz SRM dither lines into the SRCLFF path. They are a Q of 60, 40dB deep. The high Q was picked to minimize the phase distorsion - it is actually slightly too high for the line width (which is driven by coupling fluctuation.) With this modification, the SRM alignment dither can be running in LOW_NOISE in case we need it.

- We also revived the pr2spotmove.py and pr3spotmove.py scripts (stored in /ligo/home/controls/sballmer/20160927/). They move the spot position on PR2 and PR3 respectively, leaving all other things equal. We were hoping to see a change in the auxiliary loop length noise - aspecially SRCL (they are higher than O1 - see Sheila's attachment.)

- First, we moved the pr2 spot position: (PR3 by 10urad in pit and 5urad in yaw). Next we did the same for the pr3 spot position (10urad on PRM). Unfortunately we did not see any change in the auxiliary loop noise.

Comments related to this report
sheila.dwyer@LIGO.ORG - 00:08, Wednesday 28 September 2016 (30032)DetChar, OpsInfo
Link

Some additional notes:

  • The OMC DCPD impedance must have been accidentally changed during maintence today, we had been using high Z until this morning.
  • Last night's SRC alignment scheme didn't seem to have good results, when I left it on the SRM slowly became misalinged over an hour and a half and probably caused the lockloss.  The spectrum was also still changing durring this lock.  We decided to try the dither alingment in full lock, which is why we added the notches to the SRCL FF path.
  • With these notches we can now use the dither in our low noise state.  I changed the input matrix for pitch, to something that maximizes the ratio of AS 90/POP 90 (and seems to keep the cavity pole high) (-0.012 AS90, 0.05 POP90)   I added this into the ENGAGE_SRC_ASC state (which happens at 2 Watts) in the guardian, but haven't tested it yet, so if there are difficulties with this state in the morning just revert the gaurdian change.  We can't close the beam diverters with this loop closed, so operators should skip "close beam diverters" until further notice.  
  • We set the IFO to undistubred at 7:12 UTC, if this lock lasts long enough it would be good if people from Detchar can check if the SRM dither lines (4.01Hz and 5.01Hz) are causing lines in DARM. (This is our first low noise lock with these lines on)
  • We also made injections for SRCL, MICH and Intensity noise projections.  The times for SRCL are 4:10-4:20 UTC, MICH 4:56-5:16 UTC.  Watching the coupling durring these measurements, it seemed non stationary to cause trouble for feedforward. 
  • Last, the attachment is a short history of the spectra of PRCL and SRCL since the end of O1, you can see things are worse. We can try to narrow down the dates things changed better by looking more carefully in the morning.
Images attached to this comment
andrew.lundgren@LIGO.ORG - 01:35, Wednesday 28 September 2016 (30033)DetChar, ISC
Link 

Yes there is a big 1 Hz comb, presumably from the SRM dither lines. Attached plots are a 30 minute spectrum from 7:30 UTC, a little after going into undisturbed. The second plot is just zoomed in on a 10 Hz region to show the comb in more detail.

There's some funny structure here that I'd like to understand. I'll also come back to this in a little while if the lock holds, to see if anything changes.
Images attached to this comment
richard.mccarthy@LIGO.ORG - 06:23, Wednesday 28 September 2016 (30035)
Link 

Thank you for catching this.   Yes this would have been an inadvertent switch while working on the chassis.  I thought I checked it.  Must have looked before we were done working on it.  SORRY.
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