This is a quick summary of work done by many people today:
- We found that we were only using one DCPD for the last couple of days, which made shot noise bad. (Jenne's alog 37585) Fixing this improved our range from ~45MPC to ~55MPC
- We see that the low frequency noise is still bad since the EQ and that it is not coherent with anything. (Jenne's alog 37590) We checked out a few ideas about what could be responsible for this noise.
- The CARM UGF was too high causing the loop to have a good deal of gain peaking (Thomas Vo and Pep Corvas alog 3594) We reduced the gain by 1dB which helped a bit and this is now in the guardian, but this wasn't the low frequency problem.
- We tried moving the CPs since those could be in a different location than before the EQ. We saw spots from CPY on both the PRM camera and the SRM camera, where the spot is very close to the SRM spot, but moving them around makes no difference to DARM.
- We tried moving the spot on PR3 (POP A) and looking at the jitter coupling, similar to what was done in 37000. The first attachment here is directly comparable to the plot in 3700 and seems similar.
- After Jeff did some calibration measurements I quickly scanned the full range of the ETMX ESD bias to see if that made any impact on the noise. (It didn't, only the 60 and 120 Hz lines)
- We noticed that the RF9 stabilization control signal became much larger at low frequencies after the work done July 14th on RF72 (37498 and comments).
The last plot shows a couple of sensitivity curves, illustrating the problem.
Josh, TJ, Andy, Beverly,
A status update on Detchar's efforts to follow up the excess noise reported above. We haven't found anything clear yet, but there are some small oddities.
The spectra posted above look strange because the DARM noise below 30Hz is lower now than before while above 30Hz it's higher - a hint perhaps. Perhaps a filter or switch not engaged?
We ran Bruco: https://ldas-jobs.ligo.caltech.edu/~thomas.massinger/bruco_H1_July19_10UTC/
No smoking gun broadband coherence around 30-80Hz. Notable coherent things are:
- OMC DCPD NULL has non-negligible coherence at low frequencies, so maybe tuning of the DCPD combination could be improved: https://ldas-jobs.ligo.caltech.edu/~thomas.massinger/bruco_H1_July19_10UTC/OMC-DCPD_NULL_OUT_DQ.png
- The beam jitter channels, as expected.
- There is more broadband coherence now with PRCL than good times:
We checked that h(t) and DARM IN1 both see this noise (so not a calibration filter mismatch) (yellow and blue are now/bad times).
- https://ldvw.ligo.caltech.edu/ldvw/view?act=getImg&imgId=172828
- https://ldvw.ligo.caltech.edu/ldvw/view?act=getImg&imgId=172826
We started looking for a switch that says it's switched but isn't like in LLO's 33071, but there one FASTIMONs was way higher than the others, and so far we don't see that. We checked all of the L2/M2/M3 FASTIMONs and nearly all of them are the same now as they were for two quiet reference times with good range (30th of June and 4th of July). Some exceptions are (yellow and blue are now/bad times)
- PR3 M2 LL was misbehaving https://ldvw.ligo.caltech.edu/ldvw/view?act=getImg&imgId=172590 But this channel may be acting up.
- MC1 M2 was a bit higher https://ldvw.ligo.caltech.edu/ldvw/view?act=getImg&imgId=172512
- ESDAMON for ETMX was higher https://ldvw.ligo.caltech.edu/ldvw/view?act=getImg&imgId=172615
- MC2 M2 channels were lower during the bad time: https://ldvw.ligo.caltech.edu/ldvw/view?act=getImg&imgId=172563 https://ldvw.ligo.caltech.edu/ldvw/view?act=getImg&imgId=172551
- PRM M2 a bit higher https://ldvw.ligo.caltech.edu/ldvw/view?act=getImg&imgId=172543
- SR2 M2 has some bump near nyquist, maybe ringing or aliasing? https://ldvw.ligo.caltech.edu/ldvw/view?act=getImg&imgId=172542
We checked all SUS BIO MON channels and they are all in same state as the reference good times.