gabriele.vajente@LIGO.ORG - posted 08:43, Thursday 13 July 2023 - last comment - 14:10, Thursday 13 July 2023(71293)
Coherences after OM2 change
DARM coherences after OM2 was turned off and is now cold: https://ldas-jobs.ligo-wa.caltech.edu/~gabriele.vajente/bruco_DARM_1373284789_COLDOM2/
It looks like the low frequency noise has now higher than usual coherence with:
DHARD_Y: https://ldas-jobs.ligo-wa.caltech.edu/~gabriele.vajente/bruco_DARM_1373284789_COLDOM2/ASC-DHARD_Y_IN1_DQ.html
MICH: https://ldas-jobs.ligo-wa.caltech.edu/~gabriele.vajente/bruco_DARM_1373284789_COLDOM2/LSC-MICH_OUT_DQ.html
PRCL: https://ldas-jobs.ligo-wa.caltech.edu/~gabriele.vajente/bruco_DARM_1373284789_COLDOM2/LSC-PRCL_OUT_DQ.html
and adding jitter coherence for reference: https://ldas-jobs.ligo-wa.caltech.edu/~gabriele.vajente/bruco_DARM_1373284789_COLDOM2/PEM-CS_ACC_PSL_TABLE1_X_DQ.html
These excess coherences are also evident in our range (as has been mentioned elsewhere in the alog).
In the attached figure, I show both the 'usual' range that's on the wall in the control room in blue, as well as the range calculated from the GDS-CALIB_STRAIN channel (it's probably actually the CLEAN version of GDS).
We turned on the OM2 heater at the time of the T-cursor around -16 days. Prior to this time, the CAL-DELTAL channel was well matched to the GDS-CALIB_STRAIN calibration, so blue and orange overlap nicely. The lower Y-cursor is roughly around the middle of our range values for the past OM2-cold times.
During the time that OM2 was hot (up until about -1 day on this plot), both versions of the range are higher than before, although the orange calculation that takes into account our optical gain loss shows a more modest improvement than what we see on the wall (blue trace). The upper Y-cursor is roughly around the middle of the corrected-for-optical gain orange trace.
We turned OM2's heater off yesterday, and so we're back to the calibration situation where CAL-DELTAL matches GDS-CALIB. But, it's clear that both versions of our range are dramatically lower today than they were the last time we had OM2 cold. Reasons for this are still under investigation.