Following Michal’s input, I repeated the standard correlation study for Scattered Light (#64022, #64041) during the period of elevated microseismic noise (sea activity) between September 10-11, in order to identify the dominant residual source after the intervention on the West End baffle.

As a first step, I compared the glitch rate (frequency < 50 Hz, SNR > 5, noting that this rough cut also includes other types of glitches) with the BRMS between 0.1 and 1 Hz from ENV_CEB_SEIS_W, both in this recent period and during another high microseism episode, December 7-8, 2024. The current rate remains below ~8 glitches/min even with seismic velocity above 3 µm/s. In contrast, last December the rate was nearly double for comparable microseism levels. Refer to Figures 1 and 2.

I then repeated the usual analysis to search for correlations. The attached list shows the most correlated channels, along with plots of some representative cases. All channels with correlation > 0.2 are associated with the West End, F0, and F7, as in the past. A weaker correlation was also identified with some North End channels, such as Sa_NE_F0_LVDT_V, though visual inspection suggests no clear similarity between this channel’s velocity and the glitch frequency (see Fig. 5).

Time permitting, the analysis could be extended to other periods of strong sea activity. For now, however, the data support a reduction in scattered light glitch rate while confirming the West End as the primary source.

ITF found in LOW_NOISE_3 and in Science Mode. 
During the afternoon the Vertical correction of both SR and PR increased. At 17:23 UTC the SR coils started to saturate, but the ITF kept the lock. In the meantime I've contacted the SUSP Oncall (Palaia) and agreed to proceed with the recovery at the unlock.
The ITF remained locked, but also the PR coils were close to saturation. At 19:52 UTC I set the ITF in Troubleshooting Mode to allow Palaia to start the recovery, the ITF unlocked at 20:27 UTC.
ITF left in DOWN state, recovery in progress.

SBE
The SPRB Position loop opened at 20:27 UTC during the recovery of PR. Loop left open until the end of the recovery.

DET
The node DET_MAIN went in UNKNOWN state after the unlock at 20:27 UTC. Because there's no light on B1p due to the recovery of the PR, for the moment it's not possible to restore it.

Guard Tour (UTC)
17:57 - 18:29
19:55 - 20:29

The failure of the HVAC in the central building has a strong impact on the Etalon control, see Figure 1.

5:06 UTC ITF found in SCIENCE. It kept the lock for the whole shift.

Last week the B1p 56MHz signal was changed to be sampled at higher frequency of 40kHz (https://logbook.virgo-gw.eu/virgo/?r=67663), in order to check if the order 2 mode frequency noise is visible in that signal as it already is in B1. Normally the frequency noise is not visible on B1p 56MHz, because that signal is not sensitive enough, so one would not expect to see it, only the 1111Hz IMC line is visible there.

Figure 1. However, there were times last week when the noise on the first stage of the frequency stabilization was 10 times higher than normal, which also increased the SSFS error signal level at 10kHz by a factor ~10. In those data one can see coherence between the SSFS and B1p 56MHz and B1. For B1 the order 2 mode peak at ~10.6kHz is clearly visible, both in the spectrum and even more clearly in the transfer function. For B1p 56MHz there is no such feature, the coherence is flat in that frequency region around 0.4, and so is the transfer function.

My tentative conclusion is that for B1p 56MHz a different path of frequency noise coupling is dominant, so the path going through the order 2 mode being resonant in the arms at 10.6kHz is negligible and not visible. 

Tonight we had another unlock due to glitches in the PZT, see Figure 1.

Figure 1. The main effect when IPATSiA is shining in this configuration is a change in alignment. SDB1 turns in TY by 10urad, which normaly is the order of magnitude needed to add ~50% of misalignment losses in the OMC. The power in the arms decreases by 13%, which if nothing else was changing would result in a 6% reduction in DARM optical gain (it should scale as the square root of the power in the arms when the B1 power is kept constant by the DARM loop). However the optical gain decreases by 25%, which would be consistent with losses in the OMC increasing by ~35%. The power on B1p also increases by a factor 2, and the 6MHz and 56MHz sidebands on B1p become misbalanced.

Figure 2. Zooming in on the transition, the decrease in arm power has a significantly shorter time scale than the SDB1 alignment. So that change is not a consequence of the SDB1/OMC misalignment. The change in optical gain as measured by Hrec has a time scale that is in between the two. Which would indicate that there is some other degree of freedom appart from OMC alignment that is changing working point.

Figure 3. Last week IPATSiA did not have an impact on SDB1/OMC alignment, but it did have impact on the offset on B1p 56MHz I, the RF error signal for DARM. Those measurements were done in LN2 and not in LN3 with DCP at 300Hz. 

Figure 4. The image on B1p when the power increases looks like a TEM00 mode, not an order 1 misalignment mode. So it is more likely that there is an offset in a longitudinal signal that changes (for example in MICH).

An important question is if it is the effect on the different position of IPATSiA on the mirror, or if it is effect of the LN3 with 300Hz DCP configuration that we don't know well. 

This entry is meant to keep track of the current allocation of the TCS chillers across the site.

As of today:

• 3 chillers are in use for the cooling system of the main CO₂ lasers.

• 1 chiller (on loan from Roma ToV) is in the TCS room to be used as a spare.

• 1 chiller (returned two weeks ago from repair and maintenance) is in use for IPATSiA.

• 1 chiller is on loan to INJ.

ITF found locked in LOW_NOISE_3 with SCIENCE mode (Autoscience ON); BNS Range ~54 Mpc. ITF and IMC Unlocked at 04:13UTC (pdf 1) due to BS glitch(?) with high SeaActivity observed on DMS (fig.1). Automation relocked in LN3 on first attempt at 05:02UTC, SCIENCE mode set at 05:06UTC. ITF left locked.

Guard tour (UTC)
21:11 -> 21:49
23:12 -> 00:44
01:15 -> 02:00
03:14 -> 03:48

Today we carried on another IPATSiA shift. 
In the morning during the maintenance, we installed a new, more powerfull, chiller in order to solve the stability problem on the CO2 power we met last shifts. We ended the installation at 9:49UTC and switched ON the chiller and the laser, preparing the setup for the afternoon. With the new setup, the power is much more stable, with the temperature which remains into a variation of ~0.1⁰. Nevertheless, some small adjustments to the chiller parameters were still needed to avoid T drift which eventually caused some jumps on the power (see fig. 1).

We then started the study after reaching the LN3 state and further realigning the SR up to a DCP ~300Hz. In this way, we aimed at work in the cleanest possible state, with all the servo loop working on. Moreover, we removed the offset on SR_TX. 

The CO2 power stabilized at 236mW on the pickoff (with ~47mW reaching the mirror). 

At 14.35UTC  we took ~20' of  clean data in LN3 @300Hz DCP

Compared to the last position of the previous shift , I came back to the central position and moved down vertically by the same amount (up on the thermocamera, see fig. 2). 

At 15:00UTC we started shining the CO2-PA in the POSITION 1

The effect on the absorpion and BNS it's this time quite huge (see fig. 3). Unfortunately, the ITF unlocked at 15:34:52UTC, probably because the BS_TY loop diverged trying to compensate for the CMRF variation due to IPATSiA (tbc).

For this reason, in the next lock we decided to disable the servo immediately before the projection of the CO2.

At 16:45UTC: LN3 with SR@300Hz (directly) → 15’ clean data

At 17:25UTC, we started shining again, in the same POSITION 1

The effect of this point is clearly visible in Hrec (see fig. 4)

At 18:00UTC we stopped shining and moved to a new point, moving up (donw on the camera) from the central point, always by the same amount.

At 18:11:07UTC we started shining the CO2-PA in the POSITION 2. However, the ITF eventually unlocked few minutes later (18:16UTC).

At the next relock, I took some additional data in the same position, starting at 19:03 for 10' (this time with the BS servo ON again). 

At 19.13 I blocked the laser, took the ITF in the same configuration for 10' while unmounting IPATSiA to collect other clead data (at 19.18 the new chiller has been switched OFF).

I the put back the usual setting for both DoF of the SR and the BS_TY servo.

Further analysis will follow in the next days. 

ITF found in CARM_NULL_1F and Prepare_Science Mode. After some attempts the ITF was back in LOW_NOISE_3 from 14:20 UTC. The planned Commissioning activity (IPATSIA, carried out by Spinicelli, see report #67723), started at 14:03 UTC during the relock.
Activity concluded at 19:40 UTC, ITF back in Science Mode from 19:46 UTC.
ITF left locked.

On-call intervention due to the BS Server being unreachable (see entry 67712)

At around 04:40 local time, the BS Server began malfunctioning, resulting in missing BS data.
After performing a few remote checks, we decided to go on site and reset the BS crate.
Following this, we verified whether the codes were running correctly on the DSPs. Since this was not the case, we identified the issue as the auto-reload function in the DSP code being disabled.
Once corrected, the data flow resumed normally.

We also took the opportunity to install the cleaned air filters in the MC top and bottom crates (see entry 67664).

• Start of operations: 09:00 (local time)
• End of operations: 11:12 (local time)

This morning we installed one additional microphone (GRAS 46AZ) inside the Laser Lab. It is named ENV_LLR_MIC. This microphone is going to be used to monitor the acoustic noise close to air outlet during a HVAC speed-up test that we are going to do during one of the next maintenences. We gave up using the tripod because not long enough, and we positioned the microphone onto the cable tray with its anti-wind cap, in correspondence of one air outlet in the ceiling, as shown in picture 1. It is at about 30cm below the outlet. Figure 2 compares this mic with the two B&K microphones on the LB and EIB, placed underneath the plexiglass cover. The decrease below 1Hz might be due to a difference in the response, but it is not quite clear. The increase above 1kHz caould be the effect of the plexiglass cover. In the 10-500Hz region they do not differ significantly.  

I installed in /virgoDev/smartPowerStrip/Energenie/v1r0/ a linux command-line application that allows to turn on/off the switchs of the smart power strip that controls the devices connected to the tiltometer.

With the command  egctl.exe -h we can see the help:

USAGE: egctl NAME [S1 S2 S3 S4]
    NAME is the name of the device in the egtab file
    Sn is an action to perform on n-th socket: on, off, toggle or left

    i.e: egctl.exe pdu-tilt
    i.e: egctl.exe pdu-tilt off off on on

This morning to test this application I went to NEB. I found the vacuum fan connected to the switch #4 running (this fan is very near to a microphone). I successfully turned off/on this fan using the command-line application, and I left the fan running.

Note: the 220 mA fuse was replaced by a 5A fuse (and not by a 2A fuse as reported at the end of the logbook entry  #67666)

5:00 UTC ITF found in DOWN - TROUBLESHOOTING
6:00 UTC ITF in MAINTENANCE

• BS Crate Restart (Palaia, Piendibene)
• Routine Cleaning Activities (Ciardelli)
• Vacuum Tasks and Nitrogen Refill (Vacuum Team)
• MCB Recovery of Instrumented Baffle Electronics (Dattilo, Lunghini, Ballester)
• TCS Tasks
• IPATSiA - new chiller installation
• Helicopter transit (ENV): 8:13 UTC, 8:16 UTC, 8:20 UTC (approx, less close), 8:41 UTC, 8:44 UTC, 8:48 UTC, 8:51 UTC, 8:56 UTC, 9:02 UTC
• ENV DET DAQ test noise injections (Fiori, Paoletti, Tringali)
• TCS Power checks and Optrix acquisition (operator)

During maintenance, after a data loss, INJ_MAIN and DET_MAIN both went to state UNKNOWN. Troubleshooting performed by Boldrini, Casanueva, Masserot.
 

Could not perform OMC scan due to BS crate recovery

12:00 UTC ITF in SCIENCE, immediate unlock followed by numerous others.
13:00 UTC ITF left trying to lock, in CARM_NULL_1F

SUSP
(16-09-2025 04:45 - 16-09-2025 10:00) From remote
Status: Ended
Description: Server of BS became unreachable
Need to restart BS crates
Waiting for the experts to reach the site
Crate restored

I'm not sure why the fuse was replaced with one rated 20 times higher (corresponding to 1 kW of power).
Was the original fuse mistakenly rated 20 times lower, or is there another explanation?

We made several trials from remote to recover the faulty SN28 demodulation board but without success .

The SN28 demodulation board located in the DBOX_SN58-slot3 need to be replaced by a spare one .  

The last plot shows the trend of

• some temperature sensors related to the DBOX_SN28 and others located closely 
• the DAQ 100MHz clock and SQZ PLL 8MHz magnetude and phase or frequency channels
• the red line referred to starting time of the issue .

This morning we performed a measurement of the current from the DC power supply to the laser, as requested by the laser supplier.
No shutdown or restart of the laser was necessary.

WI CH laser results:

• 100% duty cycle (199 µs) → 5.1 A

• 50% duty cycle (95 µs) → 2.8 A

We also took the opportunity to perform the same measurements on the NI CH laser:

• 100% duty cycle (199 µs) → 4.7 A

These results will be communicated to the supplier to confirm whether they are within the expected range.

ITF found locked at LN3 in SCIENCE mode.
At 02:04 UTC ITF unlocked for unknown reason (TBC). After the usual cross-alignment in ACQUIRE_DRMI, the ITF unlocked and the west cavity misaligned in a strange behavior. The BS misaligned and the Server of BS became unreachable.
From VPM all was right but the signals for BS was no more available, no Corr, no Coil channels. Also the BS alignment UI was not availeble. All CoilsSbBS Rel at 0.
I contacted Susp OnCall who is checking on it.

ITF DOWN, TROUBLESHOOTING mode set.

SUSP
( - 16-09-2025 04:45) From remote
Status: On-going
Description: Server of BS became unreachable

ITF found locked in LOW_NOISE_3 with SCIENCE mode; BNS Range ~55 Mpc. ITF set to CALIBRATION mode at 15:30UTC for routine calibration activities (Calibrations with ITF locked, ENV injections, ISC injections). ITF in COMMISSIONING mode at 16:13UTC required for injections via ENV_MAIN node. ITF unlocked due to earthquake (id us7000qwch, see pdf 1) at 17:26UTC. Automation relocked to LN3 on first attempt at 18:09UTC, back to SCIENCE mode with Autoscience engaged at 18:36UTC in order to finish LSC injection. ITF left locked

Guard tour (UTC)
17:58 -> 18:33

Calibration
(times in UTC)
15:30 - 15:49 CALIBRATED_DF_SENSITIVITY
15:50 - 16:09 CALIBRATED_DF_PCAL
18:16 - 18:33 run inject_lsc.py

EnvMoni
16:13 - 17:08UTC STARTING_NOISE_INJECTIONS. Both magnetic and acoustic injections performed thanks to Tringali's help, close supervision and loudspeaker PDU bypass (entry #67562)
Acoustic injections performed under the effects of earthquake (id us7000qwch) visible as excess noise on all F0_Z loops from DMS.

On-call intervention due to the saturation of the vertical coils of the BS tower

This morning, at around 11:47 local time, I was called by the operator.
The temperature increase inside the CEB caused a drift in the coil correction values of the BS tower.
Using the motors, I adjusted the suspension and restored the vertical corrections.

• Start of operation: ~ 12:00 local time

• End of operation: ~ 13:00 local time

Today, around 12h06 UTC, h(t) was at zero for 20 seconds. At this time, ITF was not in science mode.
As shown on plot1, h(t) was at zero because Sc_NI_MAR_Z_CORR and Sc_WI_MAR_Z_CORR channels were missing for few seconds.
Same observation was done on September 11, between 15h and 18h UTC, when tests were done on the NE/WE marionnette reallocation.
As can be seen on plots 2 and 3, this time h(t) was at zero for 16 seconds but the channels Sc_{NI,WI,NE,WE}_MAR_Z_CORR were not missing.

Hrec logfile showed the following messages:

2025-09-11-15h27m55-UTC>WARNING-Incomplete vector V1:Sc_WE_MAR_Z_CORR at 1441639691
2025-09-11-15h29m27-UTC>WARNING-Incomplete vector V1:Sc_NE_MAR_Z_CORR at 1441639783
...
2025-09-11-15h34m07-UTC>WARNING-Incomplete vector V1:Sc_NE_MAR_Z_CORR at 1441640062
...
2025-09-11-16h33m27-UTC>WARNING-Incomplete vector V1:Sc_NE_MAR_Z_CORR at 1441643620
2025-09-11-16h33m27-UTC>WARNING-Incomplete vector V1:Sc_WE_MAR_Z_CORR at 1441643623
...
2025-09-11-18h00m11-UTC>WARNING-Incomplete vector V1:Sc_NE_MAR_Z_CORR at 1441648824

ITF found in Down state in Troubleshooting mode.
For the first part of the shift it was impossible to proceed with the locking acquisition due to ALS_WARM node switching to ALS_FAULT whenever there's not enough power. 
At around 6:25 UTC Casanueva went to the WE Building to restore the power on ALS WARM (see report #67708), action concluded at 6:35 UTC.
After a series of attempts the ITF was back in Science Mode from 8:20 UTC.
From 9:27 UTC to 9:39 UTC I set the ITF to Adjusting Mode to allow Soldani to change the setpoint of the CEB ACS and allow Ruggi to adjust the Vertical Coils of the BS.
The ITF unlocked at 9:44 UTC, I contated the SUSP Oncall (Palaia) to recover with the motors the BS Vertical position. Recovery concluded at 10:45 UTC, ITF back in Science Mode from 11:38 UTC.
Another Adjusting break was done from 12:28 UTC to 12:35 UTC to allow Soldani a further change of the CEB ACS setpoint.
ITF left locked.

Air Conditioning
During the morning Soldani investigated the issue with the ACS CEB started on Friday (see Oncall entry #67691). The temperature was adjusted multiple times during the shift (see attached plot).

This morning Piernicola warned us that the green generation at the WE was systematically reaching low levels, making the amplifier reach 0 at times, since there was not enough seed. I went this morning to the end building and try to place better the optical fibers. I recovered around 2.3 mW of stable seed so I let it like that. To be monitored.