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Reports until 09:12, Friday 01 November 2024
H1 General
thomas.shaffer@LIGO.ORG - posted 09:12, Friday 01 November 2024 - last comment - 15:59, Friday 01 November 2024(80990)
Pausing locking to run tests on laser glitching issue

We lost lock at some higher states in the relocking process due to the laser glitching* issue that we have been having. At this point we decided to pause locking for now to run some tests that were discussed during a meeting yesterday. The current plan is to hold at 2W with the ISS, FSS, and IMC locked. If this configuration is found to be unstable or we see excessive glitching still, then we will start to remove just the ISS or FSS, etc to narrow down the problem.

During this time, other, approved, light maintenance activities can take place.

 

*The issue may not be the laser itself, but I'm unsure what else to call this at the moment.

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sheila.dwyer@LIGO.ORG - 10:18, Friday 01 November 2024 (80991)
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We sat in this configuration from 15:34:37 UTC Nov 1 until the IMC lost lock at 16:45:34, 1 hour and 10 minutes.  The attached screenshot shows some channels at the time of the IMC lockloss, FSS fast mon and PC mon show some growing oscialltion until the time that the reference cavity transmission drops, the ISS sees a jump, and the IMC unlocks.

We've been sitting with the IMC in offline (MC2 is misaligned so the IMC won't flash), with the PMC, FSS and ISS locked since 17:09 UTC. 

 

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sheila.dwyer@LIGO.ORG - 15:59, Friday 01 November 2024 (80999)
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Summary of today's tests:

  • IMC losses lock when it's locked by itself, with PMC, FSS, and ISS.  This shows up as a drop in power in the ref cavity transmission, similar to many of our locklosses tagged "IMC"
  • When we tried sitting with the FSS locked but the IMC unlocked, we still see similar drops in power in the ref cavity transmission, although we don't know if these would have unlocked the IMC or not, they seem quite similar to the ones that unlock it, so think that they might have.
  • We measured the FSS, and became concerned that the 1.7MHz peak crosses unity in a way that might make the FSS unstable 80993.  We discussed adjusting this notch but didn't make an attempt.
  • We lowered the FSS common gain by 3dB, which has been accepted in safe but not in observe.  With this gain lowered and the ISS off, we didn't see any glitches for 30 minutes (not long enough for a convincing test)
  • We decided to try relocking with the common gain lowered.
  • I removed the redistrbution of gain in the CARM servo so we will ride out earth quakes and microseism better over the weekend, as that change didn't seem to help: 80969
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