ryan.crouch@LIGO.ORG - posted 17:13, Monday 17 July 2023 - last comment - 16:28, Wednesday 19 July 2023(71422)
OMC ASC pause test, 2.6Hz investigation
Sheila, RyanC
We did 3 rounds of setting the H1:OMC-ASC_MASTERGAIN to zero waiting 5 minutes then setting it back to its nominal 0.02.
23:31:39 H1:OMC-ASC_MASTERGAIN = 0
23:36:55 H1:OMC-ASC_MASTERGAIN = 0.02
We noticed that ADS turned off during this test, specifically H1:ASC-ADS_PIT4_OSC_CLKGAIN = 0 at 23:37:11 UTC
23:41:53 H1:OMC-ASC_MASTERGAIN = 0
23:47:09 H1:OMC-ASC_MASTERGAIN = 0.02
23:52:23 H1:OMC-ASC_MASTERGAIN = 0
23:58:01 H1:OMC-ASC_MASTERGAIN = 0.02
Here is a scope showing some OMC ASC signals during this test.
The bottom left 4 plots show the output of the OMC ASC loops, so you can use these to judge when the OMC ASC was off. The third column bottom 4 plots show witness sensors for OMC and OM3 motion, they move a lot less when the ASC is off. Please ignore the plots of the error signals (4th row, POS and ANG INMONs), these are after the MASTERGAIN so they were zero when Ryan turned off the ASC. The top row right two plots show the QPD signals that are used as error signals, no clear change in their rms with the ASC on or off, but tomorow we should plot their spectra.
Here's a comparison of several channels with the OMC ASC on and off. Conclusions: the OMC shakes a lot more when the OMC ASC is on, but this has no effect on DHARD or DARM at low frequency (below a few Hz).
So the OMC ASC loops are not responsible for the 2.6 Hz peak
There's also no evidence at this point that the OMC moving more is having an effect on DARM noise.
I attach here the omicron transients during this test from 2023-07-17 23:31:39 to 2023-7-18 00:03:01. The first figure is the time-frequency plot and second figure shows the rate of these transients per 300 seconds.
We do not see any noticeable change during this on/off test in the rate of these transients.
P.S. Thanks to Joe Areeda for running Omicron on this data.