Virgo Logbook

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Detector Characterisation (Spectral lines)

swinkels, pascucci - 17:54 Thursday 25 April 2019 (45738)

Wandering line around 100 Hz stabilizes at 83.5 Hz

Not sure if this has been seen before, but while browsing some spectrograms, we noticed that a moving line that normally hovers just above 100 Hz suddenly took a nosedive and then appeared to stabilize itself perfectly at 83.5 Hz around noon on April 22. This line does not seem to be related to the line at 186 Hz, which disappeared a few days ago, since it was still minding its own business around 100 Hz at that moment.

The operator report at the moment the line stabilized itself notes some troubles with the squeezing system, and squeezing was switched off around 12:20, while the interferometer remained locked. Were there any PLLs or similar of the squeezing system that were switched on or off at that moment? The GIPC configuration was also changed around that time, but it seems less likely that this causes some high-frequency line.

Images attached to this report

45738_1556206815_20190424_spectro_spectromedian_Hrec_hoft_20000Hz_20_210_604800.jpg

45738_1556206822_20190422_spectro_spectro_LSC_DARM_20_210_86400.jpg

Comments to this report:

mwas - 10:57 Friday 26 April 2019 (45739)

This has happened before in between Feb 18 and Feb 22 but in that case the ITF was not locked for 4 days between when the line became fixed after being wandering. It would be interesting to find when between Feb 22 and April it started to wander again (and look for a configuration).
It had also been seen before starting to wander on November 22 2018, in that link there is an investigation over a month of how that line behaves but no conclusion.
It may be related to SPRB, as when the SPRB suspension stepping motors are on there is a very large line at 84Hz, but might just be a coincidence that the two frequency are similar.