Marc, Oli

In 87713 it's noted that some of the strange behavior we've been seeing with the locks seem to be related to the ETMY L2 stage. The ETMY L2 satamp was swapped out on Oct 14th from S1100137 to S1100127 as part of the ECR E2400330 upgrade (87469). So, even though we were seemingly doing fine with this ETMY L2 satamp, we decided to swap it out this morning to see if that is the cause of our issues. Coincidentally, the spare satamp that we have available that was modified for ECR E2400330 and that Jeff had characterized was the satamp that had come from ETMY L2, S1100137. So we decided to put that one back in - it was fine before, although it obviously has now been modified for the satamp upgrade. So it's not been swapped back to exactly what it was before, but this is the closest we can get!

Marc and I took S1100137 down to EY and swapped out S1100127 with S1100137. I edited the fitresults file for S1100137 to work for ETMY L2 and replaced the previous OSEMINF 5.3:0.1 compensation filters to be the best possible compensation filters for this new satamp. 

Updating compensation filters
$ py satampswap_bestpossible_filterupdate_ECR_E2400330.py -o ETMY_L2
All updated filters grabbed for ETMY
ETMY L2 UL compensation filter updated to zpk([5.25],[0.0959],1,"n")
ETMY L2 LL compensation filter updated to zpk([5.21],[0.0953],1,"n")
ETMY L2 UR compensation filter updated to zpk([5.18],[0.0949],1,"n")
ETMY L2 LR compensation filter updated to zpk([5.21],[0.0955],1,"n")
write /opt/rtcds/userapps/release/sus/h1/filterfiles/H1SUSETMY.txt
Done writing updated filters for ETMY

Swap timeline

Satamp characterization data

Here's the characterization data and fit results for S1100137, 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_S1100137_ETMY_L2_20251020.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/
2025-10-20_UKSatAmp_S1100137_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.

Fri Oct 24 10:10:02 2025 INFO: Fill completed in 9min 58secs

To continue with the "what has changed since Monday" I have created the SDF reports. For now I've just concentrated on the OBSERVE.snap settings changes.

Models with changed settings over this time period: h1alsex  h1alsey  h1asc  h1ascimc  h1iscex  h1iscey  h1isietmy  h1lsc  h1omc  h1suspr3  h1sussr3

There are approximately 400 settings changes.

Full details available in /ligo/home/david.barker/tuesdaymaintenance/23oct2025/sdf/observe

We had a lockloss at 17:03 UTC that has the same "pulse" behavior noted by Jennie and Oli yesterday. This pulses can be seen in the DARM loop, on the L3 master out, and in the EX and EY L2 master outs. These pulses are about 5.8 Hz in frequency.

I'm going to use this post to keep running notes of the 1 Hz investigations:

• After being at high power for more than 30 minutes, we went to low noise and left DHARD P in its high bandwidth configuration.
• After some minutes, the 1 Hz oscillation appeared in the ASC
• Indication that DHARD P is NOT the only culprit here
• I averted the lockloss by running the High Gain ASC script
• after the script completed I reengaed the LSC FF since that is not the issue here
• we had been at high power long enough that the CSOFT P gain was dropped to 20, and I can't change it because the thermalization guardian won't let me
• I measured DHARD P around 1 Hz with all ASC in high bandwidth
• DHARD P looks very stable at 1Hz, the phase is fine and there is no UGF at this frequency
• at 9:54 local I transitioned all the YAW arm loops to their low bandwidth state
• LOCKLOSS at 10:03- no oscillations, no saturation warnings, just a "fast" lockloss

DHARD P at 1 Hz attached.

We have been getting saturation warnings on EY after going through the lownoise coil drivers state. We finally tracked it down to the R0 F2 and F3 drivers. The reaction chain length drive (aka reaction chain tracking) is causing these saturations. This servo is run using the L2 OSEMs as a witness to then drive the R0 chain to follow the main chain. I turned off the length drive and the saturations stopped. When I turn it back on it continues to saturate.

The only recent change I can think of is the L2 satamp swap on all the test masses.

Because we continue to have issues with the lownoise state of DHARD P (1 Hz ring up), I have commented out both DHARD P lownoise steps in LOWNOISE_ASC. This includes the engagement of FM4 (lownois reshape with low pass) and FM8 (boost). These steps are done separately. This means that we can safely run the LOWNOISE_ASC guardian state, there will just be a little more noise until we can resolve the DHARD P issues.

We had a small mains power glitch 17:25:25 Thu 23 Oct 2025 PDT. It was only reported by the OSB GC UPS.

TITLE: 10/24 Day Shift: 1430-2330 UTC (0730-1630 PST), all times posted in UTC
STATE of H1: Corrective Maintenance
OUTGOING OPERATOR: None
CURRENT ENVIRONMENT:
    SEI_ENV state: USEISM
    Wind: 8mph Gusts, 6mph 3min avg
    Primary useism: 0.04 μm/s
    Secondary useism: 0.62 μm/s 
QUICK SUMMARY: H1 was down overnight due to ongoing locking issues. I'll start by running through an initial alignment while I get caught up on events of the past couple days.

• Wind low, microseism steady around 90th percentile
• DR1 dust monitor reports no change in counts
• All other systems nominal

TITLE: 10/24 Eve Shift: 2330-0500 UTC (1630-2200 PST), all times posted in UTC
STATE of H1: Corrective Maintenance
INCOMING OPERATOR: Tony
SHIFT SUMMARY: Microseism is still slowly trending up, I got up past MAX_POWER twice, I confirmed the Roll mode damping works at 62Ws.
LOG: No log.

Lock^#1

• We sat in ADJ_POWER for a little over an hour at 50Ws as Rahul damped the Roll mode. It seems to be on ETMX. We manual-ed  to LOWNOISE_COIL_DRIVERS and later up to LOWNOISE_LENGTH_CONTROL and ETMY started to saturate (it looked to be coming from SUSETMY DAC  1, channels 1, 2, 3. We noticed that the DCPDs were growing as well and PIMON was showing some red. We then went back to ADJ_POWER and lowered the power down to 45Ws, the saturations stopped but the PI kept growing till we lost lock. Lowering the power looks to have made the PI ringup even faster?
• I set the gain of the ETMY roll mode to zero in ISC_LOCK and reloaded it. The Thermalization GRD went into error as we went into LOWNOISE_LENGTH_CONTROL since the SRCL1 offset was not at the nominal, I set the nominal back and reloaded it and it did not fix the error.

Lock^#2

• 02:42 UTC IA
• 03:48 UTC I got back to ADJ_POWER and brought us down from 62 to 40W
• 04:17 UTC Shortly after I brought us back up to 62 at Sheilas' suggestion and tried Rahuls new Roll mode damping settings and they seemed to work at MAX_POWER, after 6 or 7 minutes we tried to go to LOWNOISE_LENGTH_CONTROL. We lost lock shortly after during TRANSITION_FROM_ETMX. Sheila accepted the filter changes for the new Roll mode settings.
• 04:41 UTC Holding in DOWN

I modified Oli's script  make_EST_model.m that gets the OSEM estimator filters into the front-end models. This script is now the preferred way to get any estimator model filters into the real-time computers. The change was made to add failsafes to avoid further errors on the translation of fitted filters into foton ( see LHO: 87689 ).

For the script to work, any .mat files with estimator filters must have the following syntax:

The format for the filters can be seen in any of the .mat files listed below that live in (svnroot)/sus/trunk/HLTS/Common/FilterDesign/Estimator/. The files come with a README that indicates at how the fits inside were created

est_model_H1PR3_L_2025-10-07.mat  -- contains slightly tweaked versions of the PR3 L (and P) models reported in [LHO: 87593]
est_model_H1PR3_P_2025-10-07.mat  -- contains slightly tweaked versions of the PR3 P (and L) models reported in [LHO: 87593]
est_model_H1PR3_Y_2025-08-19.mat  -- contains the PR3 Y fits from [LHO: 86563]

est_model_H1SR3_L_2025-10-07.mat -- contains slightly tweaked versions of the SR3 L (and P) models reported in [LHO: 87612]
est_model_H1SR3_P_2025-10-07.mat -- contains slightly tweaked versions of the SR3 P (and L) models reported in [LHO: 87612]
est_model_H1SR3_Y_2025-08-05.mat -- contains the cleaned SR3 Y fits from [LHO: 86366]

These are the new .mat files that have the current OSEM estimator models. Until further notice, all previously existing .mat and .m files for OSEM estimator models/fits have been deprecated. We will later talk with Oli to standardize the addition of the OSEM estimator blends.

The updated make_EST_model.m, as well as the rest of the .mat files with the new syntax have been updated to the SUS svn under revision 12754.

Maybe the roll mode we're fighting today isn't ETMY after all?

In the attached plot, the traces are 20 min apart, and you can see that the mode we were watching at 13.75 Hz gets bigger.  Throughout this time, Rahul was changing setttings on SUS-ETMY_M0_DARM_DAMP_R, trying to get it to stop increasing.  However, when the output of the damping filter was a very small number of counts, we weren't really seeing big changes in the slope of the increase in the monitor filter H1:SUS-ROLL_ETMY_RMS_LOG10_OUTMON.  When Rahul increased the gain to 1200 (from the original of 40), we started ringing up a different mode quite quickly.  That other mode is 13.94 Hz.  

13.94 Hz doesn't match any of the roll mode monitor filters we have in place (second attachment) according to the names of the filters. But, maybe this means that ETMY is actually at 13.94 Hz, and some other optic is at 13.75 Hz?  Back in July (alog 84982 that Elenna pointed me to), we originally thought that 13.7 Hz was ETMX, but had found at that time that actuating ETMY seemed to improve things. 

Anyhow, we may also consider trying to actuate on other optics, to see if we can do anything to that 13.75 Hz mode?  While the monitor filters are all quite narrow (as they should be), the actuator filters appear to all be the same between the optics.

WP 12836
ECR E2400330
Modified List T2500232

The following SUS SAT Amps were upgraded per ECR E2400330. Modification improves the whitening stage to reduce ADC noise from 0.05 to 10 Hz.

F. Clara, J. Kissel, O. Patane