ITF found locked at LN3 in SCIENCE mode.
At 23:01 UTC ITF unlocked (TBC).
I increased the MICH_SET value up to 58 (20, 40, 60, 58) at CARM_NULL_1F. ITF relocked at LN3 at 23:53 UTC at first attempt. SCIENCE mode set.

Other
( - ) Note:
- If the sensitivity is bad after thermal transient (CARM_NULL_1F -> LOW_NOISE_3) set PR_CHROCC DAC at 4.29V with ramptime 1500 sec. (in ADJUSTING mode)
- If the sensitivity is bad after the thermal transient and the ITF unlocks, set again the PR CHROCC at 4.29V with ramptime 1500 sec and increase the MICH_SET value (after parking in CARM_NULL_1F for ~10 minutes) in steps (0->20 in 200s), (20->40 in 200s), (40->60 in 200s), (60->65 in 60s) until power on B1p decreases to ~0.02 mA and EDB_B1p 6, 56MHz upper & lower sidebands become superposed (or balanced) before progressing lock acquisition.

ITF found locked in LOW_NOISE_3 with SCIENCE mode (Autoscience OFF); BNS Range ~55 Mpc. Calibration activity (times in UTC): 21:33 - ITF in CALIBRATION mode (1h late due to daylight savings time mishap) for scheduled calibration and ISC noise injections. 21:33-21:45 CALIBRATED_DF_DAILY. 21:46-22:02 - inject_lsc.py. ITF back in SCIENCE at 21:04. ITF left locked.

Guard tour (UTC)
14:30 -> 15:10
17:10 -> 17:50
19:40 -> 20:20

Other
14:54-14:55 a small civilian biplane slowly flew over the site heading SE towards the nearby airport. It could easily be heard and seen at less than 200m altitude; is there even a no-fly zone at this point?

Other
( - ) Note:
- If the sensitivity is bad after thermal transient (CARM_NULL_1F -> LOW_NOISE_3) set PR_CHROCC DAC at 4.29V with ramptime 1500 sec. (in ADJUSTING mode)
- If the sensitivity is bad after the thermal transient and the ITF unlocks, set again the PR CHROCC at 4.29V with ramptime 1500 sec and increase the MICH_SET value (after parking in CARM_NULL_1F for ~10 minutes) in steps (0->20 in 200s), (20->40 in 200s), (40->60 in 200s), (60->65 in 60s) until power on B1p decreases to ~0.02 mA and EDB_B1p 6, 56MHz upper & lower sidebands become superposed (or balanced) before progressing lock acquisition.

ITF found in Science mode; it kept Science mode for all the shift.

Guard tours (time in UTC)

7:00-7:46; 10:45-11:30

Other
( - ) Note:
- If the sensitivity is bad after thermal transient (CARM_NULL_1F -> LOW_NOISE_3) set PR_CHROCC DAC at 4.29V with ramptime 1500 sec. (in ADJUSTING mode)
- If the sensitivity is bad after the thermal transient and the ITF unlocks, set again the PR CHROCC at 4.29V with ramptime 1500 sec and increase the MICH_SET value (After parking in CARM_NULL_1F for ~15 minutes awaiting thermal transient, lock acquisition progressed with MICH_SET steps (0->20 in 200s), (20->40 in 200s), (40->60 in 200s), (60->65 in 60s).
Power on B1p decreased from 31uA -> 23uA and EDB_B1p 6, 56MHz upper & lower sidebands became superposed (or balanced).

ITF found in LOW_NOISE_3 and in Science Mode. It unlocked at 3:12 UTC, after manually adjusting MICH SET at CARM_NULL_1F, the ITF was back in Science Mode from 4:30 UTC.
ITF left locked.

Other
( - ) Note:
- If the sensitivity is bad after thermal transient (CARM_NULL_1F -> LOW_NOISE_3) set PR_CHROCC DAC at 4.29V with ramptime 1500 sec. (in ADJUSTING mode)
- If the sensitivity is bad after the thermal transient and the ITF unlocks, set again the PR CHROCC at 4.29V with ramptime 1500 sec and increase the MICH_SET value (After parking in CARM_NULL_1F for ~15 minutes awaiting thermal transient, lock acquisition progressed with MICH_SET steps (0->20 in 200s), (20->40 in 200s), (40->60 in 200s), (60->65 in 60s).
Power on B1p decreased from 31uA -> 23uA and EDB_B1p 6, 56MHz upper & lower sidebands became superposed (or balanced).

ITF found locked at LN3 in SCIENCE mode.
We manual unlocked in order to allow Nardecchia to tune the DAS. At CARM_NULL_1F I increased the MICH_SET value step by step up to 65. ITF relocked at LN3 at 15:53 UTC. SCIENCE mode.

18:59 UTC - S251031cq

Guard tour (UTC):
19:00 - 19:35
21:00 - 21:38

Other
( - ) Note:
- If the sensitivity is bad after thermal transient (CARM_NULL_1F -> LOW_NOISE_3) set PR_CHROCC DAC at 4.29V with ramptime 1500 sec. (in ADJUSTING mode)
- If the sensitivity is bad after the thermal transient and the ITF unlocks, set again the PR CHROCC at 4.29V with ramptime 1500 sec and increase the MICH_SET value (After parking in CARM_NULL_1F for ~15 minutes awaiting thermal transient, lock acquisition progressed with MICH_SET steps (0->20 in 200s), (20->40 in 200s), (40->60 in 200s), (60->65 in 60s).
Power on B1p decreased from 31uA -> 23uA and EDB_B1p 6, 56MHz upper & lower sidebands became superposed (or balanced).

This morning, starting from the standard TCS configuration used throughout the run, we began exploring a possible DAS tuning aimed at reducing the MICH offset, which is currently around 70 (compared to ~20 measured before). A total of three steps were performed, all involving an increase of the inner ring power on the NI.

STEP 1
NI inner ring power increased by 20%.
NI PICKOFF value: 0.578 W → 0.583 W.
Action completed at 08:44 UTC.

STEP 2
NI inner ring power further increased by 20%.
NI PICKOFF value: 0.583 W → 0.589 W.
Action completed at 09:55 UTC.

At this point, we manually unlocked the ITF to test the lock acquisition.
The ITF relocked at the first attempt at CARM NULL 1F at 11:13 UTC, and, after imposing a MICH offset of about 70, it relocked at LN3 at 12:02 UTC.

STEP 3
NI inner ring power further increased by 20%.
NI PICKOFF value: 0.589 W → 0.603 W.
Action completed at 12:54 UTC.

After this step, some glitches were observed in several signals, including the BNS range (see the attached figure), suggesting a possible degradation of ITF stability. For this reason, we decided to revert the third step.
Consequently, at 14:36 UTC, I reduced the NI inner ring power back to the value of STEP 2.

Then, the ITF unlocked spontaneously at 14:50 UTC and relocked at CARM NULL 1F on the first attempt at 15:09 UTC.
The ITF reached LN3 at 15.57 UTC. 

The slow drops in BNS range observed yesterday came back at much higher rate after this morning's re-lock (Fig.1)

Zooming on a shorter window in Fig.2 shows that these drops are witnessed by a large number of signals related to the asymmetric DoFs: the power of the 56MHz sideband drops like a square wave, jumps are observable especially on the TY components of PR and BS MAR signals and the 56MHz sidebands quickly diverge from each other on the relative phase camera.

Interestingly, MICH_SET and relative error signal (DARM_PSTAB2) and SR_MAR_TY also observe events in the same moments, with SR_MAR_TY and MICH_SET showing almost identical behaviour.

Since none of these is takes the 56MHz as error signal, it seems plausible for this behavior to be driven by either the DARM demodulation that feeds the MICH_SET servo or the SR alignment, and all the other signals are just witnesses.

ITF found locked in LOW_NOISE_3 with SCIENCE mode (Autoscience ON); BNS Range ~55 Mpc. 08:30UTC - BNS Range dropped by 30 Mpc for a minute. 08:42UTC - Start of NI CH tuning. 09:08-12:30UTC - Optical bench work at 1500W SQZ lab. 10:57UTC - ITF in COMMISSIONING after 40% increase of NI DAS power and subsequent increase of B4 sidebands. 11:02UTC - ITF manually unlocked to test lock acquisition. 11:13UTC - automation achieved CARM_NULL_1F on first attempt.12:02UTC - after adjustment of MICH_SET automation relocked to LOW_NOISE_3, SCIENCE mode set at 12:05UTC. 12:45 and 13:39UTC -  Another drop by 20-30 Mpc lasting a minute was observed on BNS Range. ITF left locked.

ISC
Test of lock acquisition (times in UTC):
After parking in CARM_NULL_1F for ~15 minutes awaiting thermal transient, lock acquisition progressed with MICH_SET steps at 11:31 (0->20 in 200s), 11:35 (20->40 in 200s), 11:38 (40->60 in 200s), 11:42 (60->65 in 60s).
Power on B1p decreased from 31uA -> 23uA and EDB_B1p 6, 56MHz upper & lower sidebands became superposed (or balanced).

Other
( - ) Note:
- If the sensitivity is bad after thermal transient (CARM_NULL_1F -> LOW_NOISE_3) set PR_CHROCC DAC at 4.29V with ramptime 1500 sec. (in ADJUSTING mode)
- If the sensitivity is bad after the thermal transient and the ITF unlocks, set again the PR CHROCC at 4.29V with ramptime 1500 sec and increase the MICH_SET value (as in ISC subsystem report above) in CARM_NULL_1F.

ITF found in LOW_NOISE_3 and in Science Mode. It kept the lock for the whole shift. 
ITF left locked.

Other
( - ) Note:
- If the sensitivity is bad after the thermal transient at LN3, set again the PR CHROCC at 4.29 with ramptime 1500 sec. (set ADJUSTING mode)
- If the sensitivity is bad after the thermal transient and the ITF unlocks, set again the PR CHROCC at 4.29 with ramptime 1500 sec and increase the MICH_SET value (+74 in 300 sec) at CARM_NULL_1F.

ITF found DOWN in TROUBLESHOOTING Mode.

Planned activity performed:
- Tests with NI off-centering.
Planned activity not performed:
- Vacuum wifi WE test (Ballester, Roman)

At 12:39 UTC the valves close to BS tower were closed automatically after the failure of an electronic driver in the BS tower rack. The device has been replaced and the normal conditions has been recoverd. At 14:28 UTC the valve has been re-opened by Vacuum experts.
ITF relocked at CARM_NULL_1F at 14:38 UTC at first attempt.
Fom 15:25 UTC we started to increase the MICH_SET value (+74 in 300 sec) in order to converge the sidebands (EDB_B1p_PC_56MHz_LSB_PWR and EDB_B1p_PC_56MHz_USB_PWR) and relock ITF up to LN3.
LN3 acheived at 16:03 UTC.

- TCS DAS CHROCC tuned. TCS_CHROCC_PR / DAC_V  From 4.29 to 4.19 with ramptime 1500 sec.

16:27 UTC - SCIENCE mode.

Guard tour (UTC):
19:00 - 19:36

Other
( - ) Note:
- If the sensitivity is bad after the thermal transient at LN3, set again the PR CHROCC at 4.29 with ramptime 1500 sec. (set ADJUSTING mode)
- If the sensitivity is bad after the thermal transient and the ITF unlocks, set again the PR CHROCC at 4.29 with ramptime 1500 sec and increase the MICH_SET value (+74 in 300 sec) at CARM_NULL_1F.

In the meantime, we performed some additional data analysis to further investigate the observed effects. The following results summarize the outcomes and comparisons made with previous datasets:

• First, I verified that a beam shift occurs only on HWS-DET during the unlock, and not on HWS-INJ.
  By taking the difference between the CCD illumination patterns before and after the unlock of the last measurement 20251029T1009, no misalignment or spurious beam was observed (see Fig. 1). 

• I reprocessed the HWS-DET data from acquisition (2) – 20251028T1829, reported in entry 68051, as suggested by Alessio.
  The reprocessing took WF21, the first wavefront acquired after the unlock, as the reference.  Some WFs acquired after the unlock are shown in Fig. 2.
  Then, I extracted the curvature and compared it with the one obtained from the last measurement performed with DET (20230316T0008).
  The two results are consistent with each other, as shown in Fig. 3. The current curvature is slightly lower, possibly due to a slightly lower input and/or circulating power in the arm, or because some curvature is lost as the YAG beam effect is at the right edge of the map (i.e. the SLED beam is decentered on the NI mirror).

• I revisited the last absorption measurement performed with HWS-DET (20230316T0008), which had been reprocessed afterwards.
  Before reprocessing, considering for example the WF9, corresponding to approximately 30 s after the unlock, it appeared as shown on the right side of Fig. 4. On the left side of the same figure, the difference between the illumination profile of the reference acquired before the unlock and that acquired after the unlock is shown. Thus, comparing this difference map with the one reported in the entry  68056,  in 2023 the problem of beam displacement was more evident. Without reprocessing the wavefronts, the YAG never appears in the map (see an example is WF59- Fig. 5).
  By reprocessing the images with respect to WF8, the YAG effect becomes visible in WF9, as shown in Fig. 6, evolving over time in a manner similar to that observed in the most recent dataset.

Exploring beam position in LN3 is very slow and inconvenient. From what I remember of past tuning the speed at which the rest of the control loop reacts limit the tuning to 1mm per hour (https://logbook.virgo-gw.eu/virgo/?r=65985). In CARM NULL 1F the response is much faster, and one can do changes on a time scale of 10 minutes instead of one hour. So this type of checks should be done in CARM NULL 1F not in LN3.

ITF found in Science mode.

At 8:25 UTC ITF in Troubleshooting mode for the planned activity of NI-off centering.

In the next relocking attempts the dark fring was again too high and it prevented to reach LN3.

At 12:38 UTC, while waiting in CARM_NULL_1F, the BS large valve closed; the Vacuum team promptly reacted. Intervention still in progress.

Infrastructures

The DMS is reporting red flag for high temperature in "Piscina" the problem is already know; to mitigate the temperature Davide opened the door of the rooom

This morning I ve changed in LN3 the setpoint for NI Y. The overall stablity of the lock has been worsened by the decentering and the behavior was not showing a good direction.

Y positive:

- MICH offset reduced

- B1p increased

- B7 & B8 increased

- DIFFp TX set increased

Y negative opposed behavior but in both directions the ITF stability was worsened

As a part of the global check of the status of any part of the INJ subsystem that could be related to that recent issue we performed a mode matching measurement with the kick method (i.e. applying corrections on the end mir z and analyzing the 02 mode during the free swinging). The last measurement was done in June 2024 #64450.

We had to repeat twice the procedure because in the first attempt only the north arm data were good. At the end, the gps used for the analysis are:

- 27/10/2025 18:44:24 UTC, 102 s (North arm) 

- 29/10/2025 19:10:00 UTC, 120 s (West arm)

The analysis started 25 and 40 sec after the unlocks for the North and West respectively (so that the ITF should be still "hot"), see plots 1 and 2.

We found high values for the mismatch: around 4% for the north and 5% for the west. 

We could try to improve it by tuning the mode matching telescope.

The issue with the HWS intensity changing during the gentle unlock is a long standing story, I found several entries reporting it and discussing the solution (60377, 60362, 60344, 59433, 59434, 59347).

In one of them (59433), the issue seems to be traced back to the ETMs misalignment during the unlock (but keeping them aligned seems worse).

In any case, the only solution seems to be the re-processing of the data. 

22:00 UTC ITF found locking
22:14 UTC ITF  in LOW_NOISE_3, SCIENCE. It kept the lock for the whole shift.

Guard Tours (UTC)
22:10 - 22:44
00:12 - 00:49
02:02 - 02:40
04:16 - 04:56

ITF found in CARM_NULL_1F and in Troubleshooting Mode. It was manually unlocked at 14:36 UTC to perform a further Hartmann sensor measurement.
During the afternoon, Gosselin performed a measurement of Mode Matching with Kick, which I repeated at 19:09 UTC.
ITF back in CARM_NULL_1F from 19:35 UTC, from 20:40 UTC I started to increase the MICH_SET value (see attached plot). As the value of B1p and Sidebands was improving, I attempted to fully lock the ITF.
ITF back in LOW_NOISE_3 and Science Mode from 22:14 UTC.

To investigate the hypothesis that the structure in the upper part of the HWS map is caused by the green beam, Diego modified the automation configuration to keep it OFF after the unlock. We then performed a new measurement with HWS-DET. For this purpose, I switched OFF the HWS-INJ SLED and switched ON the HWS-DET SLED.

The ITF was locked at CARM NULL 1F at 11:04 UTC. Acquisition started at 14:28 UTC (folder 20251029T1528), and the ITF gently unlocked at 14:36 UTC (WF14).

The structure was also present in the maps (see figure).
The measurement was interrupted, and the lock acquisition was restarted.

ITF found at CARM_NULL_1F in TROUBLESHOOTING mode.
At 09:20 UTC, under request of I. Nardecchia, I unlocked ITF in order to allow the planned activity on WI absorption measurement.
Activity in progress...

This morning we proceeded with the HWS-INJ measurement to assess the absorption of the WI.
The ITF was locked at CARM NULL 1f at 07:41 UTC.
The HWS-DET SLED was switched OFF, and the HWS-INJ SLED was switched ON and set to 1.6 V.
The acquisition started at 09.09 UTC [20251029T1009]. The HWS illumination pattern is shown in figure 1. 
We unlocked the ITF in a gentle way at 09.21 UTC (WF 22).
The YAG effect is visible in the maps (see for example WF 56 in Fig. 2.
We also extracted the curvature from the maps and compared it with the last measurement performed last year [20240801T1703 -  64836]

The measured curvature is consistent with the previous measurements (see the third figure).
The measurement was interrupted at 10:46 UTC (WF 180).

With the purpose to shed some more light on the HWS measurement, we have analyzed the raw images before and after the appearance of the feature in the upper part of the wavefront.

Figure 1 shows the difference between the two raw images. As it can be seen, there is a significant modification of the illumination pattern on the HWS as soon as the ITF has unlocked. The change in the illumination pattern is responsible for the appearance of the feature.

This change in the illumination pattern can be explained with a displacement of the HWS probe beam (due to a misalignment of one of the optics or benches along the path) or with some spurious other beam (1064 nm or 532 nm) reaching the HWS plate. With the available data, it is not possible to discriminate between the two effects, even if a check of the LC signals (figure 2) seems to exclude the displacement of the probe beam.

22:00 UTC ITF found in TROUBLESHOOTING just unlocked from CARM_NULL_1F. I tried to lock with SR ty+2 misalignment but B1p was unstable/too high and ITF unlocked twice.
I left the ITF in CARM_NULL_1F: pic1 shows the drifts in B1p_DC and in the balance of the sidebands during the shift

Guard Tours (UTC)
22:30 - 23:20
00:26 - 01:02
02:31 - 03:07
04:16 - 4:55

Due to the instability of the ITF of the last period, we started a global check of the status of any part of the INJ subsystem that could be related to that problem.

We measured the modulation index of the 6MHz and 56MHz by scanning the RFC with the INJ in standalone. The scan, back and forth, of a duration of 500µs for 500µm of displacement, started at  ~13.31UTC (see fig. 1).

The resulting modulation depth for the 6MHz and 56MHz are, respectively,  ~0.2 and ~0.21 as expected.

As discussed during the daily meeting of Monday, we restored the global thermal settings to the nominal values of last weeks, including the PR Chrocc correction. 

We started setting the nominal DAC voltage  (4.14) on Monday evening (see fig. 1), and waiting the thermalisation, that was expected during the night. However, due to some hysteresis, both heating temperature and circulating current didn't reached the nominal values. In order to restore the correct setpoint, we tuned the DAC voltage (+0.2V then -0.05V) after the maintenance. 

As a result, the sideband slightely increased and the global behavior of the ITF seemed more reliable. Nevertheless, the fringe remains ~50% higher than usual.