Rahul is working to identify which optic this problematic 13.75 Hz mode is, and so has been actuating on ITMY.  We're now seeing a mode at 13.87 Hz with the ITMY actuation, so I think ITMY is absolved from being the problematic optic.

Attached plot is during ITMY actuation.

I am able to ring up 13.75 Hz by actuating on ETMX roll - see attached plot.

I was able to ring up this mode and then damp it down using the following settings - FM2+FM3+FM4, Gain -200 (-60 deg phase filter) for ETMX @53W input power. This needs to be checked at higher power and at NLN.

As per Elenna's suggestion - we will start with damping ITMY roll mode first.

ETMY roll mode gain will be set to zero for the next lock.

Filter Module changes since Monday.

the following models have had filter module changes since Monday:

h1sus[mc1, mc2, mc3, pr3, sr3]

h1isietm[x, y]

h1asc

The full list of filter differences can be found in /ligo/home/david.barker/tuesdaymaintenance/23oct2025/filter_diffs

We did a comparison of the FF drives before and after Tuesday, posting here for reference:

The first three are from two days ago with overall MICH FF gain =2, the last three are from earlier today with MICH FF gain =4.

The forst three are from NLN, the second three from low noise length control this morning when we had the MICH FF on.

These filters have been updated in both PR3 and SR3. The estimator is still off though!

Jenne asked me to check a line around 27 Hz, this does show up in max power  (today see brown trace) but also was there in max power before maintenance Tuesday this week (pink trace).

It doesn't seem to really show up in the NLN state (red trace is before maintenance, blue is one of our locks from early this morning).

My conclusion from Jennie's plot is that that 27 Hz mode isn't a major cause for concern; it's not something new that's giving us trouble.

Locking attempt 1 this morning:  Locked to full power, Oli ran the asc high bandwidth script (userapps/isi/h1/scripts/revert_asc.py) premptively to avoid having problems with the 1 Hz ring up.  

The last thing this script does is sets the LSC FF gains to 0, 45 seconds after this finished we had a sudden large increase in noise first at 300 Hz in DARM (ETMX ESD) and DHARD then 0.1 second later in CHARD, which unlocked the IFO.  This happened in the close beam diverters state, but is probably not related to the beam diverters.  This is a different problem than what we've been seeing overnight. 

No gains or anything else in the CHARD or DHARD filter banks were changed in those 45 seconds either, which rules out some other rogue change

Elenna and I commented out the DHARD boost from low noise ASC, because it takes 45 degrees of phase at 1Hz and so leaving it off may help our improve our 1Hz problems.  This boost was added to improve the stationarity of SRCL to DARM coupling by reducing the DAHRD RMS 77857.  We are leaving it off for now because we can probably go to observing without it if we can stay locked.   

Next locking attempt we sat for over an hour at full power, without doing the LOWNOISE ASC step.  

We had ETMY saturations when we ran through the ESD transitions, and they continued after DARM was switched, until Elenna turned off LSC FF.  When we turned the feedforward back on ETMY didn't start saturating.  However, at the time that the PRCL and SRCL feedforward came on, the roll mode started ringing up.  We lost lock a few minutes into this ring up, but the amplitude was much smaller than the locklosses from this mode overnight (about a factor of 100 lower).  

We aren't sure if the roll mode was the cause of the lockloss or not.

19:31 UTC Observing

FYI -- we went into observing with the ITMY PUM sat amp OSEM PD's still dead. We turned OFF the ITMY L2 (PUM) to R0 "damping" feedback loop, so the failed sensors *should* not have any impact on the IFO. However, an obvious, loud ~92-93 Hz feature remained new and glaringly obvious in the DARM sensitivity. 

@DetChar / @CW Group Probably best to just veto this observation stretch, unless we -- in the future -- find some amazingly exceptional event. 
     2025-10-16 19:31 UTC to 19:54 UTC.

ITMY L2 (PUM) Sat Amp S1100148 installed on 10/14/2025. Replaced on 10/16/2024 with S1100080.

https://alog.ligo-wa.caltech.edu/aLOG/index.php?callRep=87469

Here's the characterization data and fit results for S1100148, assigned to ITMY L2's ULLLURLR OSEMs.

This sat amp is a UK 4CH sat amp, D0900900 / D0901284. The data was taken per methods described in T080062-v3, using the diagrammatic setup shown on PAGE 1 of the Measurement Diagrams from LHO:86807.

The data was processed and fit using ${SusSVN}/trunk/electronicstesting/lho_electronics_testing/satamp/ECR_E2400330/Scripts/
plotresponse_S1100148_ITMY_L2_ULLLURLR_20250917.m

Explicitly, the fit to the whitening stage zero and pole, the transimpedance feedback resistor, and foton design string are:

The attached plot and machine readable .txt file version of the above table are also found in ${SusSVN}/trunk/electronicstesting/lho_electronics_testing/satamp/ECR_E2400330/Results/
2025-09-17_UKSatAmp_S1100148_D0901284-v5_fitresults.txt

Per usual, R_TIA_kOhm is not used in the compensation filter -- but after ruling out an adjustment in the zero frequency (by zeroing the phase residual at the lowest few frequency points), Jeff nudged the transimpedance a bit to get the magnitude scale within the ~0.25%, shown in the attached results. Any scaling like this will be accounted for instead with the absolute calibration step, i.e. Side Quest 4 from G2501621, a la what was done for PR3 and SR3 top masses in LHO:86222 and LHO:84531 respectively.

Here's the characterization data and fit results for S1100119, assigned to ETMX L2's ULLLURLR OSEMs.

This sat amp is a UK 4CH sat amp, D0900900 / D0901284. The data was taken per methods described in T080062-v3, using the diagrammatic setup shown on PAGE 1 of the Measurement Diagrams from LHO:86807.

The data was processed and fit using ${SusSVN}/trunk/electronicstesting/lho_electronics_testing/satamp/ECR_E2400330/Scripts/
plotresponse_S1100119_ETMX_L2_ULLLURLR_20250916.m

Explicitly, the fit to the whitening stage zero and pole, the transimpedance feedback resistor, and foton design string are:

The attached plot and machine readable .txt file version of the above table are also found in ${SusSVN}/trunk/electronicstesting/lho_electronics_testing/satamp/ECR_E2400330/Results/
2025-09-16_UKSatAmp_S1100119_D0901284-v5_fitresults.txt

Per usual, R_TIA_kOhm is not used in the compensation filter -- but after ruling out an adjustment in the zero frequency (by zeroing the phase residual at the lowest few frequency points), Jeff nudged the transimpedance a bit to get the magnitude scale within the ~0.25%, shown in the attached results. Any scaling like this will be accounted for instead with the absolute calibration step, i.e. Side Quest 4 from G2501621, a la what was done for PR3 and SR3 top masses in LHO:86222 and LHO:84531 respectively.

Here's the characterization data and fit results for S1100118, assigned to ITMX L2's ULLLURLR OSEMs.

This sat amp is a UK 4CH sat amp, D0900900 / D0901284. The data was taken per methods described in T080062-v3, using the diagrammatic setup shown on PAGE 1 of the Measurement Diagrams from LHO:86807.

The data was processed and fit using ${SusSVN}/trunk/electronicstesting/lho_electronics_testing/satamp/ECR_E2400330/Scripts/
plotresponse_S1100118_ITMX_L2_ULLLURLR_20250916.m

Explicitly, the fit to the whitening stage zero and pole, the transimpedance feedback resistor, and foton design string are:

The attached plot and machine readable .txt file version of the above table are also found in ${SusSVN}/trunk/electronicstesting/lho_electronics_testing/satamp/ECR_E2400330/Results/
2025-10-14_UKSatAmp_S1100118_D0901284-v5_fitresults.txt

Per usual, R_TIA_kOhm is not used in the compensation filter -- but after ruling out an adjustment in the zero frequency (by zeroing the phase residual at the lowest few frequency points), Jeff nudged the transimpedance a bit to get the magnitude scale within the ~0.25%, shown in the attached results. Any scaling like this will be accounted for instead with the absolute calibration step, i.e. Side Quest 4 from G2501621, a la what was done for PR3 and SR3 top masses in LHO:86222 and LHO:84531 respectively.

Here's the characterization data and fit results for S1100127, assigned to ETMY L2's ULLLURLR OSEMs.

This sat amp is a UK 4CH sat amp, D0900900 / D0901284. The data was taken per methods described in T080062-v3, using the diagrammatic setup shown on PAGE 1 of the Measurement Diagrams from LHO:86807.

The data was processed and fit using ${SusSVN}/trunk/electronicstesting/lho_electronics_testing/satamp/ECR_E2400330/Scripts/
plotresponse_S1100127_ETMY_L2_ULLLURLR_20250916.m

Explicitly, the fit to the whitening stage zero and pole, the transimpedance feedback resistor, and foton design string are:

The attached plot and machine readable .txt file version of the above table are also found in ${SusSVN}/trunk/electronicstesting/lho_electronics_testing/satamp/ECR_E2400330/Results/
2025-09-16_UKSatAmp_S1100127_D0901284-v5_fitresults.txt

Per usual, R_TIA_kOhm is not used in the compensation filter -- but after ruling out an adjustment in the zero frequency (by zeroing the phase residual at the lowest few frequency points), Jeff nudged the transimpedance a bit to get the magnitude scale within the ~0.25%, shown in the attached results. Any scaling like this will be accounted for instead with the absolute calibration step, i.e. Side Quest 4 from G2501621, a la what was done for PR3 and SR3 top masses in LHO:86222 and LHO:84531 respectively.

ITMY L2 (PUM) Sat Amp S1100148 installed on 10/14/2025. Replaced on 10/16/2024 with S1100080.

https://alog.ligo-wa.caltech.edu/aLOG/index.php?callRep=87515

Note that the satamp for ETMY L2 has now been swapped back to a S1100137, which has been modified for ECR E2400330. 

alog: 87722