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Reports until 14:41, Tuesday 05 December 2023
H1 TCS (DetChar)
camilla.compton@LIGO.ORG - posted 14:41, Tuesday 05 December 2023 - last comment - 15:54, Thursday 07 December 2023(74617)
ITM HWS Camera Sync Frequencies Adjusted to 7Hz for DARM Comb Search

Ansel, Camilla

This morning we found that the 0.98Hz DARM comb was related the the ITMX HWS camera 1Hz sync frequency, see alog 74614 where I adjusted ITMX from 1Hz to 5Hz at 20:10UTC. This was a past issue with an expected fix in place 44847 FRS4559.

Ansel then suggested that the 4.98Hz DARM comb 68261 could also be from HWS as we have nominally used a 5Hz sync frequency on the ITM HWSs during O4. At 22:25UTC I adjusted both ITMX and ITMY camera sync frequencies from 5Hz to 7Hz (instructions).

In May we had the ETM HWS and camera off for 1 week 69648, but I didn't repeat the test with the ITMs, ETMY is currently off, ETMX has 15Hz camera frequency.

Comments related to this report
ansel.neunzert@LIGO.ORG - 15:59, Tuesday 05 December 2023 (74625)
Link

Yep, as hypothesized:

  • H1:PEM-CS_MAG_LVEA_OUTPUTOPTICS_Y_DQ sees the 4.98 Hz comb as well (it's visible in earlier plots; just confirming here that it matches the spacing seen in DARM)
  • Adjusting the camera sync frequencies to 7 Hz moves the comb to about 6.98 Hz.

Plots attached.

  • Figure 1 (previous test with better labels): 19:00 UTC, ~1 Hz and ~5 Hz visible.
  • Figure 2 (previous test with better labels): 20:15 UTC, ~5 Hz visible
  • Figure 3 (this test): 22:30 UTC, ~7 Hz visible.

More precise comb spacings for future reference / searchability: 0.996785 Hz, 4.98425 Hz, 6.97794 Hz.

Images attached to this comment
evan.goetz@LIGO.ORG - 17:15, Tuesday 05 December 2023 (74630)
Link 

Another nice find! This is good news to clean up more of the H1 spectrum. I hope this one can also be turned off in observing. Any others? Potentially there might be one at 9.5 Hz since we're also seeing a problematic 9.48 Hz comb.
ansel.neunzert@LIGO.ORG - 15:54, Thursday 07 December 2023 (74667)
Link

This change does also affect the comb in DARM, as expected. Yesterday's (Dec 6) daily spectrum shows that the near-5Hz comb has been replaced by a near-7Hz comb. (Figure attached, see points marked with blue squares.)

Two combs being related to the HWS of course raises suspicion that there could be more, so I'll also mention a couple of things I checked that are probably *not* due to HWS.

  • There is a near-30 Hz comb that's been present throughout O4. I was suspicious that might be associated with the 15 Hz ETMX camera frequency. Even though we didn't see an effect back in May when the ETM HWS and camera were off, I figured it was possible that we had missed something, especially since early-O4 data is harder to interpret with more fluctuations in uptime etc and these combs are not very strong. However, the near-30Hz comb shows up strongly in CS magnetometers rather than EX ones, and it was present in magnetometers when the ETM HWS were off.
  • Monthly Fscan spectra (with gaps due to cluster issues recently filled in, many thanks to Evan Goetz) reveal the 9.47/8 Hz comb triplet in CS magnetometers as well. That's worth investigating more in its own right, but those combs are present at usual in Dec 6 data (and during the May test in magnetometers), and there's nothing running at 9.5 Hz that I know of.
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