The SR RH was switched off at 19:14 UTC.

The morning shift started by relocking the interferometer, which had no issue on that front for the whole shift.

The idea of the shift was to start studying again the SRC longitudinal detuning. Before starting that, and also because we are now working decentering, a very basic set of angular noise injections was done (DIFFp, PR). The log file is in /virgoData/NoiseInjections/ASC/ASC_injection-1476000002.txt

After that, the tests on the SR detuning started; the first few tests were done naively by changing the setpoint of the SRCL_SET loop, which in the past did not give very good results, as the signal was not carrying enough information to drive it properly in the intended way (higher frequency for the optical spring). This happened in LOW_NOISE_3_ALIGNED.

Here the recap of the tests done in this way:

08:14:10 UTC : SRCL_SET_SET = 0.5 -> 5.0 in 300 s, then 480 s of clean data;
08:27:30 UTC : SRCL_SET_SET = 5.0 -> 10.0 in 300 s, then 600 s of clean data.

Around 8:31 UTC we observed some bursts of noise in the MICH loop (and, fainter, in the SRCL one) at around 3.6 Hz. Given that in that state the UGF servo loops are not operational anymore (with the exception of the DARM one), the gains of both of them were raised around 8:35:30 UTC. We unlocked at 8:38:52 UTC.

In the following lock, that started at 09:16:53 UTC:
09:27:42 UTC: SRCL_SET_SET = 0.5 -> 10.0 in 600 s
09:46:39 UTC: unlock

There were a couple of unattended tests during the lunch break, which look very similar and probably do not carry more information.

Later, we verifired offline from the tests that the OS signal moved back to a more manual approach: LOW_NOISE_2 state, SRCL_SET loop technically close but in reality frozen in place (LSC_SRCL_SET_CAL = 0), then LSC_SRCL_SET moved manually as a static offset.

Test #1:
12:29:00 UTC: start of LOW_NOISE_2
12:33:00 UTC: SRCL_SET loop frozen (value of _SET_TOT at the time ~ -8.3)
12:33:52 UTC: SRCL_SET = 0 -> -5 in 300 s
12:41:00 UTC: SRCL_SET = -5 -> -10 in 300 s
Noise injection on DARM (and clean data): logfile in /virgoData/NoiseInjections/LSC/LSC_injection-1476017575.txt
13:01 UTC: SRCL_SET = -10 -> -15 in 300 s
13:20 Noise injection on DARM (and clean data): logfile in /virgoData/NoiseInjections/LSC/LSC_injection-1476019008.txt
13:29:21 UTC: unlock
We continued to change the SRCL set at step LN2 (in order to have all the servo for the gains active) and we took :

- DARM OLTF measurements to fit the OS for different SRCL set

- Angular noise coupling (DIFFp) to see if the coupling could change with the SRCL set

the gps are:

SRCL set @ -10 gpsDARM=utc2gps(2026,10,14,14,32,45); dur DARM=120;

SRCL set @ -20 gpsDARM2=utc2gps(2026,10,14,14,47,50); dur DARM2=120;

            gpsDptx=utc2gps(2026,10,14,14,57,00); dur Dptx=120;

            gpsDpty=utc2gps(2026,10,14,15,04,10); dur Dpty=120;

It is visible that the -20 configuration shows a lower coupling of DIFFp TX (Figure 1)

After that we tried a SRCL set up to -30 but it failed the LN3 aligned state transition (a 3.5 Hz oscillation on MICH - most probably low gain, which is surprising since we let the servos to adjust the gain in the SRCL set increase and to stabilize).

We have then reached the LN3 aligned configuration and performed a SRCL detune to check the sensitivity (to be able to compare with the one that will be achieved with the diaphragm)

RECAP

the overall changes in the violins notches are the following: 4 notches for the first violins modes in the region 412-415 Hz.

we removed an old second order mode notch at 882.17 Hz, moved down to the  2nd order frequency mode of the new violin: 827.1 Hz, Q ratio=100.

The overall effect on DARM OLTF are negligible for the bandwidth; loss of less than 2 deg at 150 Hz; change of ~12.5 deg at 491 Hz, (already considered during the notch design) compensated by retuning the SR alignment phase. See fig.1 and 2 where the overall phase of the new notches is shown. 

Just two possible hints:

The first is an old entry (... too old) dating 2011 which mentions one 54.8 Hz mechanical mode of WI payload: https://logbook.virgo-gw.eu/virgo/?r=30230. Indeed, most of the payload has changed since than, so I guess this must be just an unlucky concidence (!)

The second observation concens the attached plot. I picked some of the signals for which the BruCo found a coherence at the little one at 53.92 Hz. Couriously, these signals, which belonng to the SDB1 (OB) suspension have a peak at 54.7x Hz which appear to match closely to the main Hrec one... but no coherence on this. I do not have an interpretation for this.  

In preparation for the SR tower opening, I switched off the HWS-DET SLED at 09:25 UTC:

• 2026-10-14 09h25m18 UTC    ilaria 'EDB_DAC:TSC DET SLED [Constant value=0,Ramp time=1]' sent to EDB

Both HWS-DET and HWS-INJ SLEDs are now switched off (see HWS CCD images in Figs. 1 and 2).

ITF found in COMMISSIONING mode and CARM_NULL_1F state.
All times are UTC.
14:08 ITF back in LOW_NOISE_3_ALIGNED after the earthquake, and ready for calibration activity. The lock lasted few minutes and violin modes around 400 Hz and its harmonics were visibile in the sensitivity with high SNR, the cause of this excitation has to be identified. After the unlock the injected power was lowered too much by the automation (9W on INJ_IMC_TRA_DC) and the direct consequence was the RFC not able to lock, issue fixed by manually increase the injected power.
14:30 - 15:00: Inspection at WEB entrance for water leakage (Fabozzi with external company).
15:16 - 16:06 CALI: IM/EM actuator calibration (Verkindt, Rolland). Interrupted by the operator when CALIBRATED_DF_PCAL where completed.
16:07: Manual unlock in order to perform OMC scan in CARM_NULL_1F state.
16:49 - 18:14 DET: CARM NULL OMC SCAN in CARM_NULL_SCAN_ON state (Gouaty, #69915).
18:29 - 19:45 ISC: ITF in LOW_NOISE_3_ALIGNED, LSC/ASC noise budget (Boldrini Bossilkov, #69916).
20:40 Manual unlock. Requested LOCKED_ARMS_IR.

ITF left in COMMISSIONING mode and LOCKED_ARMS_IR state.

Guard tours:
- 20:41;

We supported the activity of DET/CAL and, at the end of the shift, adjusted the amplitudes for the SRCL and DARM injections in the inject_lsc.py script.

We started an injection of 10 mins tranches for each dof + clean data before leaving.

During the afternoon shift, we performed a scan of the OMC in CARM_NULL.

The scan was started at 16h49 utc, after the end of the 10 min timer of ITF_LOCK. We manually interrupted the scan at 18h14 utc. See attached figure.

Taking into account the thermal transient of 1 hour after reaching CARM_NULL, the best data to look at for this scan is between 17h40 and 18h14 utc.

we made it so

2:00 UTC A signal of possible failure from a HVAC INJ chiller or boiler was registered (see pic). It was not a failure and the explanation is the following: HVAC control loops are slow to avoid fluctuations, the night was colder than usual and the heating loop started compensating with a time scale much bigger than the day-night one. Heating power was temporarily increased to catch up with the gradient (Romboli, Soldani) 

06:00 UTC ITF found in LOCKED_ARM_IR state COMMISSIONING mode, set to DOWN state MAINTENANCE mode

Activities performed during maintenance:

• TCS power checks and TCS thermal camera procedure (Cantini, Galoppini, Zaza)
• CEB, clean rooms and filter cavity area cleaning (external company)
• WE Hymo maintenance (external company, Ciardelli, Fabozzi)
• TCS chiller refill (Menzione)
• Nitrogen refill (VAC group)
• INJ OMI chiller level sensor troubleshooting (Cantini, Galoppini, Melo, Zaza)
• WI DSP resynchronization (Boschi)

10:36 UTC ITF in  LOCKED_ARMS_IR after realigning the mirrors
12:22 UTC CITF alignment interrupted by the earthquake
12:23 UTC Earthquake 6.5 Mwp off the coast of Liberia (Atlantic Ocean), ITF set to EARTHQUAKE mode
13:34 UTC ITF in COMMISSIONING mode, arms locked
13:40 UTC ITF in LOCKED_ARMS_BEAT_DRMI_3F, beginning of commissioning activity

I ve checked again the SR demodulation phases for LN2 

the SR ty is correctly 1.96 (in the entry there was a problem of copy and paste of the initial phase but the delta was correct)

for SR tx the phase should be reverted back to 3.8 as written in the entry  69889

Attached to this entry,  the details of the TolmFrameBuilder servers and the Imaging servers related to this event .

• all the TolmFrameBuilder servers running with a frame dt of 0.2s complains to not be able to sent theirs frames to the FbmFFE  server running on olserver52
  • the FbmFFE server reports to not receive any input frame during 21s
  • Most of the TolmFrameBuilder servers succeeded to return in theur standard running conditions, except the SUSP_Fb one where some actions were mandatory
• all the Imaging servers and the TolmFrameBuilder servers running with a frame dt of 1s complained to not be able to sent theirs frames to the FbmMain  server running on olserver52
  • the FbmMain server  reports to not receive any input frame during 26s

It's difficult to distantly if the issue is due to the network or a temporary overload of the main DAQ host, olserver52

Figure 1 compare the position of the order 2 mode as seen on B1 between before and after the change in input mirrors and EM RH retuning. The spread of the peaks of frequency noise coupling due to the order 2 mode are similar to what they were in the past, but the exact shape is different, which is not surprising. A 100Hz decrease in frequency correspond to a 2m decrease in mirror radius of curvature. This means that the two arm cavities are still within +/-2 meters of each of each other, with differences most probably due to astigmatism.  It may still be possible to decrease further the order 2 mode by RH tuning, if we are lucky and the astigmatism in the two arms happen to be the same. During the large steps of EM RH during the initial tuning the B1p went through a minimum, and that minimum is ~20% lower than the current B1p power, but there is no guarantee as the B1p power also depends on other thigns (etalon, alignment, etc) than just the EM RH tuning.

There is also an average translation by ~100Hz towards lower frequency, which would mean that on average there is 2m less radius of curvature in the two arms.

https://logbook.virgo-gw.eu/virgo/?r=66937

Today we took the spare OMI chiller that was in the Optics Lab to the Chiller Room in CEB. The idea was to swap the chillers but the spare didn't work as expected (the chiller couldn't reach the setpoint temperature) and we decided to leave the current chiller running as it was. 

We performed two tests: 

- We put the level sensor in another water container in order to investigate the oscillation observed since 30/09 (Fig. 1). During the test period (red zone in the figure), we can see that the oscillation is not present, so our conclusion is that probably the sensor is mechanically interfering with the temperature sensor inside the water container of the OMI chiller and creates this oscillation.
The oscillation on the level signal is correlated to the oscillation on the temperature signal (Fig. 2)

- The second test was to verify the pH of the water inside the OMI chiller. The background measurement was a pH and chloride test on ultra pure water just poured from the filtering system: pH 5.5, no chloride detected (Cl- < 0.1 ppm). The water that has been running inside the OMI chiller and into the utilities had a pH of 6.7 and Cl- < 0.1 ppm. This is a further proof of chemical reactions happening (corrosion, for example). It could explain the debris we find in untreated ultra pure water cooling systems.

During the locks of October 9, Hrec and its new version HrecOS (which uses a new optical reponse model adapted to detuned SR and that includes an optical spring) were running.
Plot1 shows unbiased hrec/hinj values from Hrec. We observe for the modulus a residual bias around +2% at low frequency and around -2% at high frequency (>100 Hz).
During those locks, SR was tuned and plot1 shows that in this configuration, Hrec provides a residual bias that can be improved but that is reasonable (during O4 this residual bias was around 1%).

Plot2 shows a comparison of hrec/hinj at 37, 207 and 407 Hz, between Hrec and HrecOS. We can see that HrecOS provides hrec/hinj modulus closer to 1 and hrec/hinj phase closer to 0. That's an encouraging result. We will see how it behaves when SR is detuned...
Plot3, shows the sensitivity curves from Hrec and HrecOS and check that Hrec and HrecOS provide almost the same sensitivity over all the frequency band.

This afternoon, after recovering CARM NULL 1F, we performed an absorption measurement using HWS-DET.

After approximately one hour of stable lock, the ITF was manually unlocked in gentle configuration, keeping all optics along the HWS-DET optical path aligned, including NE.

• 16:21 UTC: HWS acquisition started (dataset: 20261012T1821).

• 18:26 UTC: Gentle unlock performed (wavefront 9). 

Since this was our last opportunity to perform measurements with HWS-DET before the baffle installation scheduled for next week, I asked to continue the data acquisition for the remaining hour of the shift.

A preliminary comparison with the ANSYS simulation indicates an absorption of approximately 38 mW in the NI mirror (see Fig. 1).

At 12 W, the circulating power was estimated to be around 80 kW. Scaling this to the current input power of 17.5 W gives an estimated circulating power of approximately 116 kW.

Based on an estimated absorbed power of 35 mW, this gives a WI absorption of approximately 0.3 ppm.

After completing the measurement at 19:29 UTC, we switched the CHs back on, and Fabio left the ITF in the arms locked on IR configuration.

The SR+arm double cavity pole (DCP) has been disappointingly low, and the power in the arms increased more than what would expect from looking at the carrier recycling gain. The simple explanation for both effects is that the arm cavity finesse has changed.

The new input mirrors have a transmission of 1.30% https://tds.virgo-gw.eu/?r=21813, while the old mirrors had a transmission of 1.35% https://tds.virgo-gw.eu/?r=11316, a 5.6% change. One would expect the arm cavity finesse to increase by 5.6% and consequently the DCP decrease by 5.6%, about 23Hz. Which would mean that the DCP of ~395Hz is in fact comparable to the ~420Hz we had before changing the input mirrors. 

The effect on arm power is a bit less evident, as the increase in arm finesse increases the ratio between the power in the arms and the power in the power recycling cavity, but it also increases the losses as light circulates more times in the arms. In an example Optickle simulation with 75ppm RTL in the arms the power in the arms increases only by 2% when changing the input mirror transmission from 1.375% to 1.30%, and the power in the PRC decreases by 3.5%. 

In addition the change in arm cavity finesse should also change the MICH->DARM coupling, I would guess reducing it by ~5.6% in amplitude.

The attached plot and its zoom  shows the evolution over 1 week of

• the NARM_BEAT DC and 157MHz magnitude signals
• the WARM_BEAT DC and 154MHz magnitude signals

According to this plot, the NARM_BEAT_DC and 157MHz magnitude values decreased the  2026-10-07-19h08m-UTC 

The standard values have been recovered this morning .

Operations performed between 2026-10-12-07h34m58-UTC and 2026-10-12-07h44m04-UTC 

Below some comments

• it is strange to see the minimum of the BEAT_DC signal close to zero during the tuning phase for NARM 
• raw data plots related to the BPC tuning
  • NARM_BEAT : full BPC tuning sequence, beginning of the BPC tuning, end of the BPC tuning 
  • WARM_BEAT : full BPC tuning sequence, beginning of the BPC tuning, end of the BPC tuning
• maybe some parameters of the BPC BEAT tuning have to be retuned (experts are informed)

ITF found in locked arms IR.

In the first part of the shift Alain performed a relignment of the WE green beam.

After that at around 8:15UTC the ITF was locked in CITF and Ilaria performed the CH tuning.

Then the commissioning team worked at the locking recovery of CARM_NULL_1F, recovery still in progress.

Susp

SR LC opened by the guardian at 7:15 UTC, properly closed.

Today was devoted to CH tuning, as the ITF, when cold, requires several lock acquisition attempts before reaching a stable lock, allowing it to gradually warm up.

The tuning shift started at 10:00 LT to allow Alain to adjust the green beam alignment beforehand.

Initial configuration:

I decided to increase the WI CH power for the following reasons:

1. The WI DAS was tuned to compensate for an absorption level twice that of NI. Therefore, I would expect the WI CH power to be approximately twice that of NI.

2. The plots below, provided by Matthieu, show the evolution of the matching after unlock for both NI and WI. While the NI matching remains relatively stable, the WI matching shows significant variations.

The goal of the tuning  was to maintain the same sideband level in DRMI immediately after an unlock as in DRMI without a preceding ITF lock (see Fig.1).

STEP 1: increase the WI CH by 20 % (completed at 07.18 UTC):

Since the change was in the right direction, I proceeded with a second step in the same direction of STEP 1.

STEP 2: increase the WI CH by further 20 % (completed at 08.45 UTC):

The sideband behaviour during the tuning are shown in Fig. 4

After that, the lock acquisition systematically failed at CARM NULL 3/3. Madda addressed the issue by increasing the DIFFp phases to +0.4 and reducing the DARM gain from 0.014 to 0.01.

Diego and Manuel are currently proceeding with the retuning of the lock acquisition.

During last maintenance, we changed the modulation frequencies ot the WI and NI horizontal accerlerometers to an higher value not multiple of 50 Hz. We fixed the problem. This issues happened in the past but, since the values were not saved in the DSP code file (.hrd file), the wrong ones have been restored after a reboot. 

On Saturday 10 October 2026, 14h17 UTC, I have done a reload config of CALnoise process (while ITF was unlocked) to add three injected permanent calibration lines at 12.9, 13.9 and 14.9 Hz.
They replace the lines previously mentioned at 10.8, 12.8 and 14.8 Hz. The amplitude of the lines are a first estimate that may be updated once the ITF is locked.