The first attachment shows spectra (GDS CALIB STRAIN clean, so with calibration corrections and jitter cleaning updated and SRCL FF retuned) with OM2 hot vs cold this week, without squeezing injected. The shot noise is slightly worse with OM2 hot, while the noise from 20-50Hz does seem slightly better with OM2 hot. This is not as large of a low frequency improvement as was seen in December. The next attachment shows the same no squeezing times, but with coherences between PRCL and SRCL and CAL DELTAL. MICH is not plotted since it's coherence was low in both cases. This suggests that some of the low frequency noise with OM2 cold could be due to PRCL coherence.
The optical gain is 0.3% worse with OM2 hot than it was cold (3rd attachment), before the OMC swap we saw a 2% decrease in optical gain when heating OM2 in Decmeber 74916 and last July 71087. This seems to suggest that there has been a change in the OMC mode matching situation since last time we did this test.
The last attachment shows our sensitivity (GDS CALIB STRAIN CLEAN) with squeezing injected. The worse range with OM2 hot can largely be attributed to worse squeezing, the time shown here was right after the PSAMs change this morning 78636 which seems to have improved the range to roughly 155Mpc with cleaning; it's possible that more psams tuning would improve the squeezing further.
Times used for these comparisons (from Camilla):
- no sqz OM2
hotcold 24/06/2024 12:18:00 UTC - no sqz OM2
coldhot 24/06/24 23:52:10 UTC - sqz with psams adjusted OM2 hot 25/06/2024 13:34:52 UTC
- sqz OM2 cold 16/06/2024 11:51:20 UTC
Side point about some confusion caused by a glitch:
The first attachment shows something that caused me some confusion, I'm sharing what the confusion was in case this comes up again. It is a spectrum of the hot no sqz time listed above, comparing the spectrum produced by dtt with 50 averages, 50% overlap, and BW 0.1 Hz (which requires 4 minutes at 15 seconds of data), compared to a spectrum produced by the noise budget code at the same time. The noise budget uses a default resolution of 0.1Hz and 50% overlap, and the number of averages is set by the duration of data we give it which is most often 10 minutes. The second screenshot shows that there was a glitch 4 minutes and 40 seconds into this data stretch, so that the spectrum produced by the noise budget shows elevated noise compared to the one produced by dtt. The third attachment shows the same spectra comparison, where the noise budget span is set to 280 seconds so the glitch is not included and the two spectra agree.
Comparison of sensitivity with OM2 hot and cold wihtout squeezing:
The next two attachments show spectra comparisons for no sqz times with OM2 hot and cold, (same times as above), the first shows a comparison of the DARM spectrum, and the second shows the range accumating as a function of frequency. In both plots, the bottom panel shows the difference in accumulated range, so this curve has a positive slope where the sensitivity of OM2 hot is better than OM2 cold, and a negative slope where OM2 hot is worse. The small improvement in sensitivity between 20-35 Hz improves the range by almost 5Mpc, then there is a new broad peak at 33Hz with OM2 hot which comes and goes, and again a benefit of about 4Mpc due to the small improvement in sensitivity from 40-50 Hz.
From 90-200 Hz the sensitivity is slightly worse with OM2 hot. The coupled cavity pole dropped from 440Hz to 424Hz while OM2 warmed up, we can try tuning the offsets in AS72 to improve this as Jennie and Keita did a few weeks ago: 78415
Comparison of with squeezing:
Our range has been mostly lower than 160 Mpc with OM2 hot, which was also true in the few days before we heated it up. I've picked a time when the range just hit 160Mpc after thermalization, 27/6/2024 13:44 UTC to make the comparison of our best sensititivites with OM2 hot vs cold. This is a time without the 33Hz peak, we gain roughly 7 Mpc from 30-55 Hz, (spectra and accumulated range comparisons) and loose nearly all of that benefit from 55-200 Hz. We hope that we may be able to gain back some mid frequency sensitivty by optimizing the PSAMs for OM2 hot, and by adjusting SRM alignment. This is why we are staying with this configuration for now, hoping to have some more time to evaluate if we can improve the squeezing enough here.
There is a BRUCO running for the 160Mpc time with OM2 hot, started with the command:
python -m bruco --ifo=H1 --channel=GDS-CALIB_STRAIN_CLEAN --gpsb=1403531058 --length=400 --outfs=4096 --fres=0.1 --dir=/home/sheila.dwyer/public_html/brucos/GDS_CLEAN_1403531058 --top=100 --webtop=20 --plot=html --nproc=20 --xlim=7:2000 --excluded=/home/elenna.capote/bruco-excluded/lho_excluded_O3_and_oaf.txt
It should appear here when finished: https://ldas-jobs.ligo.caltech.edu/~sheila.dwyer/brucos/GDS_CLEAN_1403531058/
(Jenne, Jordan, Gerardo)
On Monday June 24, I noticed an increase on pressure at HAM6 pressure gauge only. Jordan and I tried to correlate the rise on pressure to other events but we found nothing, we looked at RGA data, but nothing was found, then Jenne pointed us to the OM2 thermistor.
I looked at the event on question, and one other event related to changing the temperature of OM2, and the last time the temperature was modified was back on October 10, 2022.
Two events attached.
Some more analysis on pressure vs OM2 temperature in alog 78886: this recent pressure rise was smaller than the first time we heated OM2 after the start of O4 pumpdown.