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Reports until 17:10, Friday 01 November 2019
H1 SQZ (SQZ)
sheila.dwyer@LIGO.ORG - posted 17:10, Friday 01 November 2019 - last comment - 17:47, Friday 01 November 2019(52896)
FSS cross over problem: glitches in DARM come and go with squeezer beam diverter.

In the attached screenshot, you can see that the highfrequency glitches in DMT omega have gone away and come back 3 times, each of those was times that the squeezer was blocked. Looking at the 12 hour summary of DMT omega, we can see that these glitches started aroudn the same time that our range degraded.  These glitches aren't showing up in omicron.

The other main observation that we have about the squeezer in this lock is that there is a slow osciallation in the RF power reported by the 3MHz OMC demod (3rd attachment).  The strange thing about this is that the reported RF power stays high and noisy when the squeezer is blocked.  This points to some kind of a problem coming from the IFO light. The 4th attachment shows that the FSS PC mon is well correlated with the OMC 3MHz demod RF mon, this was a time when the squeezer beam diverter was closed, but it is also true when the beam diverter is open. 

There does seem to be some continuing problems with the FSS. Keita is investigating the FSS.   He has some nice movies.  We also found a similar problem descirbed in a series of comments: 46717 Based on this we lowered the FSS fast gain (5th attachment), which seems to have reduced the glitches in DARM seen by DMT omega, also the range has increased, although we don't know that these things are related.

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keita.kawabe@LIGO.ORG - 17:47, Friday 01 November 2019 (52903)

First attachment is the video capture of the dtt looking at FSS IOP channels before our adjustment. You can clearly see that something was close to instability at around 20kHz and was breathing.

Second one is after adjustment.

We're not sure if this solved anything, but the FSS OLTF should have changed while UGF stayed the same. We might want to measure the IMC OLTF on Tuesday.

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