Reports until 04:45, Wednesday 14 August 2019
H1 General (DetChar)
corey.gray@LIGO.ORG - posted 04:45, Wednesday 14 August 2019 - last comment - 02:33, Thursday 15 August 2019(51255)
High Freq 500 to over 7kHz) Noise Observed Over 45min

Starting at ~9:31 utc have noticed elevated levels for DARM BLRMS bands:

The noise went off and on for 45 min (so far) and looks to start/stop suddenly and then last on the order of a minute and over 10mins (attachment#1 is the DARM blrms where you can see the steps up in noise over most of the 45min.  Time periods for some of these are about:

NOTE:  H1 range did not take a hit during this time.  It's been almost 2hrs since this noisy period last occurred.

Images attached to this report
Comments related to this report
thomas.massinger@LIGO.ORG - 05:17, Wednesday 14 August 2019 (51260)DetChar
Link

This high frequency noise is also visible in the FSS mixer and IMC-F, see attached spectrograms.

Images attached to this comment
andrew.lundgren@LIGO.ORG - 13:46, Wednesday 14 August 2019 (51272)DetChar, ISC, PSL
Link 

To answer Jeff's question in 51268, yes this is the same kind of noise in 51053. The spectra in the NPRO and the FSS are very similar. See the attached plots (green is a reference, blue the recent noise, and orange the previous occurrence). It's hard to tell is the NPRO is the cause or if it's just feedback from the FSS.
Images attached to this comment
jason.oberling@LIGO.ORG - 14:22, Wednesday 14 August 2019 (51274)DetChar, PSL
Link

Andy/DetChar, could this be related to the high frequency noise seen at the end of May (first documented here; looking at DARM plots it already looks different to me...)?  If so, there is a temporary solution until I can get into the enclosure to tweak up the FSS RefCav (as done back in May).  The FSS RefCav TPD took a dive over the weekend (a storm system passed through) and I was unable to recover much of it yesterday; low RefCav TPD has been linked to high-frequency noise in the past.  If it's not related, then this is something new.

andrew.lundgren@LIGO.ORG - 02:33, Thursday 15 August 2019 (51291)DetChar, ISC, PSL
Link 

Jason - It doesn't really look the same, unless it's a much weaker version of what we're seeing now. There's no real excess on the NPRO, and the noise on the FSS is much less. The attached spectrum has the FSS mixer signal for the May noisy time in red and the August noisy time in green. The reference time for May and August are almost identical.

The first instances of the new noise were on Aug 5 and 6, before the RefCav TPD started to drop. So there's not a direct connection. Still, it could be worth changing the FSS gain next time this happens, if the run manager agrees.

I think the best diagnostics of this noise are a 3 to 10 times broadband increase in FSS fast, or a bubble above a few hundred Hz in FSS mixer. Keita has suggested running the following DTT template when the noise is recognized:

/ligo/home/keita.kawabe/Templates/FSS_highfreq.xml
Images attached to this comment