Reports until 16:07, Thursday 08 December 2022
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jenne.driggers@LIGO.ORG - posted 16:07, Thursday 08 December 2022 - last comment - 16:46, Wednesday 14 December 2022(66265)
New frequency of interest at 20863 Hz

I was trying to look at why we seemed to have a fast lockloss after ~3.5 hours earlier this afternoon.  So far I don't have a conclusion on that, but I did find that there is perhaps a new freqency of interest that we should be watching in our fast DCPD channel.

Attached is the spectrum of the fast DCPD A channel, at a few different times before the lockloss.  Blue is "well" before the lockloss, green is about a minute beforehand, brown is 24 seconds before lockloss, and pink is ~1 second before lockloss.  The peak at 20,863 Hz increases by 2 orders of magnitude in this time.  However, the maximum peak value is a little more than 10 counts, while the peak at 10.4kHz is sitting quiescently at about 2000 counts.  So, I don't think that this peak is itself causing the lockloss, unless it really rings up *fast* in the last second or so. 

The RMS of the 1 second before lockloss (measured at 200 Hz) is 2799 counts.  The RMS well before lockloss (at the time of the blue curve) is 2218 counts.  The new 20.8 kHz peak does increase the RMS (as shown in the second attachment), but it still (in these plots) doesn't look like it's going to cause a saturation of the DCPDs. So, no real conclusion on the lockloss, but certainly a frequency to keep an eye on.

I believe that our ring heaters are in the same situation as they were when we were able to stay locked for ~5 hours a few weeks ago, but we now have more annular CO2. 

Edit: The time series leading up to the time of lockloss doesn't reveal anything to me.  The dominant frequency even the moment before lockloss in the 64kHz channel is the 10.4 kHz line, so I'm not finding evidence of the 20.8 kHz peak ringing up, unless it's growing really really fast.

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jenne.driggers@LIGO.ORG - 10:45, Friday 09 December 2022 (66277)

This same frequency came up after our 13 hour lock overnight, again within the last ~minute.  The range maybe dropped a few mins before I start seeing this peak in the DCPD PI channel, and again it is much lower in amplitude than the quiescent 10.4 kHz peak.  So, not sure what's going on or if this is causing our locklosses at all, but it's still something to watch.

daniel.sigg@LIGO.ORG - 15:37, Wednesday 14 December 2022 (66373)

The frequency of the big peak is 10431.5kHz, or exactly half the ferquency of this new peak at 20863 kHz. So, I suspect this is simply the first harmonics. Also, at the begining of the lock the 10.4 kHz peak is only at 10 counts rms.

daniel.sigg@LIGO.ORG - 16:46, Wednesday 14 December 2022 (66377)

Attached a plot of the rms monitor for the 8-12 kHz region.

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