After the WI pump failure, WI suspension is moving quite a lot, more with respect to the usual, fig.1.

I don't know if this is related to the failed locking attempts, tomorrow the problem will be better addressed.

ITF still in recovery - TROUBLESHOOTING at the beginning of the shift, which kept on going through the afternoon
Here  the steps taken during the recovery and the edits to automation (Pinto, Spinicelli, Nardecchia, Was, Ruggi). LN2 was achieved three twice (18:30 UTC - vac pump failure, 19:57 UTC) lasting only a few minutes in both cases.
18:30 UTC Vacuum pump failure, fixed (Vacuum Team)
20:43 UTC ITF in LN2
20:56 UTC unlock, then unlock at LOCKING_CARM_NULL_1F (21:06 UTC), REDUCING_CARM_OFFSET_2_OF_3 (21:20 UTC), LOCKING_CARM_NULL_1F (21:30 UTC)
At the end of the shift, as instructed, I left the ITF in LOCKED_ARMS_IR - TROUBLESHOOTING, since it had not been possible to keep a stable lock in LN2 or to reach CARM_NULL_1F during the other locking attempts.

Today we continued the recovery of the ITF. We managed to reach LOW_NOISE 2.

At the beginning we noticed a lower power values on the 112 and 12 MHz sidebands, which was taken care of by Ilaria, acting on CH:

NI CH = 0.577W -> 0.708 W

WI CH = 0.324 W -> 0.416 W

At the end, we partially reversed the NI CH PWR increase: 0.708 W -> 0.630 W. (17.32 UTC finish of the actions).

After this, we had several issues in finding a good configuration of demodulation phases in order to get past the handoff from 3f to 1f in CARM null. In particular DIFFp was showing during the transient some misbehaviour (not entirely clear the rigth explanation), in which with good phases both I and Q (on TX DoF) were witnesses of some movement which ended up in a quick drift of the alignment and eventually the unlock. Curiously enough, the phase able to get past the initial transient was showing a ~45 deg mistuning. After several trials in which we noticed this behaviour, we implemented a double condition in the automation in which we use two phases, one 'wrong' for the transient and one good for the steady state (similarly to what we do for B4 56 MHz).

With this configuration we were able to lock the OMC, after a tuning of the OMC locking phases, and go up to LOWNOISE 2. However, after a while we unlocked due a to a WI tower pump failure. Antonio went to CEB  to take care of it.

We leave the ITF locking on LOWNOISE2 for the night, to acquire some statistics on the acquisition.

N.B. the modification on the automation are the following:

ITF_LOCK.py: added lines 4681-82; 4685-86.

ITF_LOCK.ini, in the SHUTTER section: added the steady state DIFFp phases.

If the acquisition is robust enough, tomorrow we will proceed to fine tune all the several phases, if needed.

:)

Also SC is aligned into the OPA. The heighest peak is 0.2% of TEM00

ITF found in LOCKED_ARMS_IR in TROUBLESHOOTING mode.
SIB2 position loop found opened. Properly closed.
ITF relocking up to CARM_NULL_3F after the usual cross-alignment in ACQUIRE_DRMI.
ITF phase tuning in progress up to CARM_NULL_1F.

This morning around 11 LT the Krakow POLGRAV team (Michal Ostrowski and Jerzy Kubitsz) installed two high sensitivity and low noise magnetometers near to the Virgo EXTternal magnetometer (ENV_EXT_MAG_N). The two magnetometers have been oriented along the geographic North, which in our location is approx +4 deg with respect to the magnetic North. Sensors are connectew with a local supply and DAQ synchronized with GPS.

It has been checked that the magnetometers are not saturating: their dynamic range is 19nT RMS, and the actual measured RMS is approx 5nT RMS.   

The plan is to record 24 hrs of data and then move to another location. Before removing this installation some magnetic pulses will be injected locally in order to test the sensors synchronization.   

ITF found in LOCKED_ARMS_IR State and TROUBLESHOOTING Mode.
ITF recovery ongoing after NI CO2 Laser RF Driver replacement (see #68263).
All times are UTC.
15:12 TCS Chillers Guardian restored with slightly higher flow (Menzione, Nardecchia).
19:07 Activity on ITF recovery concluded with ITF able to reach CARM_NULL_3F. ITF to be left in LOCKED_ARMS_IR (see #68841).
ITF left in LOCKED_ARMS_IR State and TROUBLESHOOTING Mode.

Fabio and Suzanne successfully replaced the RF driver of the NI CO2 laser (see Fig 1). To perform the intervention, the 220 V line was completely disabled from the electrical panel in the TCS room and re-enabled once the operation was completed.

The lasers (both CH and DAS) were switched on at 14:31 UTC, and the lost power was recovered (see Fig. 2).

[Nicola took care of re-engaging the Guardian system.]

A thermal image of the rings was acquired for a quick check, and the rings appear to have returned to their pre-blackout conditions (see Fig. 3).

After waiting for the strongest thermal transient to settle, and following a phase tuning performed by Manuel, the CITF locked and the sideband levels returned to values consistent with the pre-blackout conditions (see Fig. 3).

After that, Manuel and Diego started working on the lock acquisition (see entry 68841).

Today we continued with the recovery of the ITF.

From DRMI 1f we managed to reach carm null 3F, by tuning the demodulation phases of mostly 56 MHz and 169 MHz (MICH SRCL DARM and DIFFp), plus some less invasive tuning on PRAA and PRCL. We will continue the recovery  next week.

As the NI DAS has been repaired and seem to be making a similar correction to what was the case before the blackout of last weekend. I have restored the nominal offset of 350um on the SDB1 B5 QD2 V around 16:06 UTC.

ITF found in LOCKED_ARMS_BEATING.

At around 7:45 UTC, in agreement with Ilaria, Nicola switched off the TCS chiller guardian to allow the activity of Ilaria: CO2 laser temperature scan for DAS rings recovery

The replacement of the NI CO2 RF driver was completed around 14:30 UTC; after that Nicola went in TCS chiller room to reactivate the guardian.

At the moment we are waiting for the thermal stabilization of the TCS.

ISC

Etalon setpoint changed under request of Maddalena, see the log from LSC_Etalon_Acl process:

• 2026-03-06 09h23m03 UTC    berni 'NI:NI Set point [NI_RH_SET=18.695,rampTime=259200]' sent to LSC_Etalon_Acl
• 2026-03-06 09h23m24 UTC    berni 'WI:WI Set point [WI_RH_SET=18.802,rampTime=259200]' sent to LSC_Etalon_Ac

SBE

SDB2 loop opened by the guardian; vertical position recovere and loop properly closed at 12:53 UTC.

This morning we attempted to reproduce the laser temperature corresponding to the pre-blackout configuration (26.8 °C) in order to try to recover the previous DAS rings.

After Nicola disengaged the Guardian system, I progressively increased the CO2 laser temperature.

NI set-point adjustments:

• 09:29 UTC: from 19.01 °C to 20.0 °C

• 10:01 UTC: from 20.01 °C to 21.0 °C

• 10:23 UTC: from 21.0 °C to 22.0 °C

• 11:01 UTC: from 22.0 °C to 23.0 °C

• 11:26 UTC: from 23.0 °C to 23.3 °C

• 11:34 UTC: from 23.3 °C to 23.5 °C

At around 13:40 UTC I checked the DAS rings again, but no changes were observed (see figures).

It was then decided to proceed with the replacement of the NI CO2 RF driver. Fabio and Suzanne are currently working on it.

Today at 13h10 utc U adjusted again the offset of the B1_PD3_DC channel by +0.12 uW.

Today Fabio switched off and on the DDS pf the fiber noise cancellation system. After that we recovered the INJ pick off for the main PLL and we easily managed to locke the PLL.

After that I locked the FC on green. I saw a very big shift in vertical that I recovered with +130 steps of SQB1 M1. After few hours we went back to +90. Still to chceck.

All it is reovered except the alignment of SC into the OPA that it is not yet checked.

Upon arrival (at 15:00 UTC) I found ITF locked at LOCKIED_ARMS_BEAT_DRMI in TROUBLESHOOTING mode and commissioners at work to recover the standard state of ITF.
A better TCS tuning is needed in order to improve the sidebands power. Tomorrow it will be done.

Activities concluded at 20:50 UTC.

Around 18:30 UTC I was contacted by Madda due to low sideband power observed in CITF.

A check of the power levels of the different TCS actuators did not reveal any value significantly different from the nominal ones that could justify such a change in the operating point and the observed reduction of the sideband power.

I then briefly inspected the thermal camera images and noticed that the NI DAS rings appear different compared to the pre-blackout configuration (see Fig. 1). In particular, a clear relative misalignment between the two rings is visible, and the power distribution along the vertical direction of the outer ring is non-uniform.

These changes are most likely related to a change in the laser working point, as the main laser power dropped by about 50% after the blackout (as usual, every mistake has a price).

Then, together with Michal and Madda, we performed two DAS power steps to evaluate whether the observed misalignment could be partially compensated by tuning the actuator power.

STEP 1: 18:31 UTC – NI OUTER RING POWER INCREASED BY 10%
PICKOFF: 0.58 W → 0.64 W

Following this change, the sideband level decreased further (fig.2). Therefore, the step was reverted and the power was instead reduced.

STEP 2: 20:08 UTC – NI OUTER RING POWER DECREASED BY 20% WRT STEP 1
PICKOFF: 0.64 W → 0.51 W

This configuration was left for the night.

We have continued the recovery having the same issue in the lock of the DRMI that was experienced the day before.

The "lock" was achieved but the SRCL corrections start immidiately to drift

after long analysis we realized that no current was sent to the SR mirror coil. Fabio found a temporary box relay which went in the wrong state due to the shutdown. Fabio simply bypassed it.

Then we have tuned the phases up to carm step 3/3 but we experienced very low sidebands in the CITF so we decided to not waste more time in tuning and we did a step of DAS to anticipate the work of the morning (at least to understand the direction of tuning for tomorrow).

Noticing that the B1p beam was lower than usual on the camera (and the B1p galvo were opening) we removed the offset of 350 um in the B5_QD2_V signal. Offset is now 0. This correction was applied around 17h00 utc.

In addition we corrected the B1_PD3 offset at 17h19 utc by +5.3 uW.

This morning I found the two cavities locked; once recovered the SDB2 vertical position we went on with the ITF lock recovery, all the morning was spent trying to lock the DRMI, the central interferometer has finally stable locked at the end of the shift, the lock recovery will go on in the afternoon.

SBE
recovery of SDB2 vertical correction with F1 step motors from 6:50UTC to 7:05UTC.

This morning (March 5, 2026) around 8:30 UTC I went to the external cabinet hosting the electronic box to install a new battery (CSB UPS 12360 7 F2, see Figure 1), the installation was completed at 8:53 UTC. The box was closed and placed back inside the cabinet (see Figure 2).
At 11:45 UTC I went to DET EERoom to check the power supply and it was erogating 0.34 A, 24 V (see Figure 5), the hardware is operating correctly since it is not erogating the maximum current set (~0.8A), with the battery disconnected the erogated current was 0.15 A.
Figure 3 shows the comparison of ENV_EXT_MAG_N signal on May 25th 2024 (orange plot), Februaty 1st 2026 (purple plot), and March 5th 2026 (blue plot). The reference time are choosen to make sure that no tarins are passing trhough the Pisa-Empoli railway (see #68641).
Figure 4 shows the last 24 h of data.

Indeed, that effect was visible in the past also on the INJ/PSL signals (fig.1) but with a much smaller effect compared to what is seen now(fig. 2). 

This may be due to the fact that, starting from 22nd of October 2024, we are using one of the chiller borrowed by TCS team for the Neovan electronics (located in EEROOM). Thus, a check of the settings of this chiller is planned for today.

Between Monday and Tuesday morning a full recovery of the control system of the suspensions and BPC was required after the power interruption: all DSP boards have to be restarted and control loops verified. The recovery went smoothly, a part from two issues:

• The WI DSP board #31006 connected to vertical accelerometer failed to boot. Instead of replacing it (action that would require the change of both the other accelerometer board, the change of D-BOX, and the re-design of the controllers), we re-programmed the FPGA. That fixed the problem and the board was put back in the Sa_WI crate.
• TANGO servers were not available and the DC motors could not be used. For that reason OB and NI have to be recovered on Tuesday.

A similar feature was observed in the past from the cooling system of the CO2 main lasers, which produced a 1 Hz comb visible in the UPS current and voltage monitors. This comb disappeared when the chillers operated in “power-save” mode. The signal observed here could therefore be related to a similar mechanism.

It would be useful to verify how the devices were powered back on and check which operating mode they are currently in.

Past investigations:

https://logbook.virgo-gw.eu/virgo/?r=63358

https://logbook.virgo-gw.eu/virgo/?r=63357

https://logbook.virgo-gw.eu/virgo/?r=40113