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Reports until 10:45, Thursday 06 July 2023
H1 DetChar (DetChar)
ansel.neunzert@LIGO.ORG - posted 10:45, Thursday 06 July 2023 - last comment - 09:12, Wednesday 26 July 2023(71108)
1.6611 Hz comb re-appeared June 27

Perhaps unsurprisingly given its previous history, the strong 1.6611 Hz comb that disappeared (alog 69791) in late May has resurfaced. It shows up clearly in Fscans; I did some additional digging and it looks like the first traces appear on June 27th in the 12:00-14:00 UTC range. This corresponds in time with some of the work described in alog 70849, but OM2 heater changes don't account for the previous disappearance of the comb; Sheila confirms that heater wasn't on earlier in May. So it's still not clear what's going on.

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ansel.neunzert@LIGO.ORG - 14:31, Friday 07 July 2023 (71144)
Link

Update: it's coherent with H1_PEM-EX_VMON_ETMX_ESDPOWER48_DQ and H1_PEM-EX_VMON_ETMX_ESDPOWER18_DQ, and *not* with CS or EY VMON channels.

(Last time we tried to hunt this comb down, I think we didn't have high resolution coherence plots generated to high enough frequencies for these channels.)

Plots attached. The gray dots are harmonics of a separate 99.9989 Hz comb.

Images attached to this comment
evan.goetz@LIGO.ORG - 12:34, Wednesday 19 July 2023 (71507)DetChar
Link 

It looks like the behaviour of this comb changed again on July 13, shifting slightly in frequency, before then disappearing again on July 14. It is as yet unclear what caused the changes.

The attached weekly average Fscan From July 12 - 19 shows these changes around 280 Hz especially.
Images attached to this comment
evan.goetz@LIGO.ORG - 09:12, Wednesday 26 July 2023 (71726)
Link 

This comb seems to reappear between 7:30 and 9:00 UTC on July 19, 2023. Hopefully this time range can point to something that specifically changes. See attached daily Fscan image
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