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

Curiously, the same 1 Hz comb appears in the current of all three IPS phases, with an amplitude similar to the peaks seen in the UPS line’s R phase.

Nothing relevant is present in the MCB monitors.

An example of the locks of the CITF of yesterday. THere was an modulated oscillation present, that can't be blamed to a loop oscillation.

The IB tower magnetometers show the strongest 1 Hz comb magnetic component, indicating a possible source in the nearby area (LL or INJ_EE_room) powered from a single UPS phase (R phase).
The same 1 Hz comb is visible in the CEB magnetometers and in the External Magnetometer, even though the latter is located at a significant distance from the CEB.

It is also worth noting that the UPS is located very close to the IB tower, a configuration that may account for the higher magnetic level measured by the tower magnetometer.

At the beginning of the shift the  SDB2 intervention and the  MC transfer function checks (INJ) were ongoing; both activities were concluded around 16:00 UTC.

The SDB2 evacuation started around 16:00 UTC; at around 16:30 UTC I was able to close the SDB2 loops.

Then I tried to recover the proper status for DET_MAIN that did not go in SHUTTER_CLOSED; to solve the issue I contacted the DET on-call and he fixed the problen at around 17:00 UTC.

After that I locked the cavities and Julia started the lock recovery, see Initial recovery.

ITF left in locked arms.

Vacuum

The SDB2 pumping was stopped around 17:30 UTC.

We started the recovery by turning on the BPC of the green beams, and aligning also the signals at the level of the injection. Then it locked without problems.

We then aligned the central interferometer and we tried to lock. The signal of PRCL that uses the 6MHz seemed almost well tuned (initially was 1.6 and it seemed that 1.4 was better, but this had almost no impact). Instead the signal of 56MHz seemed wrong (when engaging the loops, SRCL seemed to diverge). However it is not easy to tune it, since we use I and Q for MICH and SRCL. We have tried to change it until we were able to lock (initially 3.24, we changed until 2.0 and we manage to get short locks). However the lock do not last.

In parallel we noticed that the alignment signals were also mistuned, so we tried to tune them better, however the phase that seemed good for the H didn't seem good for the V (initially 3.2 and seemed ideal one for H was 2.2 - we checked the sign). So I left the phase unchanged and I commented the alignment in the CITF (1829-1830 in DRM1_LOCK.py), to give us some margin to align by hand and see if the lock would last longer. I managed to tune the phases and to close the vertical alignment loop by hand, so I reimplemented it in the automation. I left the horizontal open for the moment.

In the meantime I called Ilaria to check the ChroC since we didn't expect to tune phases (the arms and the RFC didn't need further tuning). She made a small step of the chroc to try to match the previous temperature. I didn't see any change on the demodulation phases. To be checked better tomorrow.

The 1Hz "sidebands" observed in the laser power signal comes from the power subbly of the central building. Especially in the ENV_CEB_UPS_CURR_R channel. These sidebands were not present before the blackout.

We opended the SDB2 air tank in order to replace the Ethernet switch that was not reachable.

In order to access the switch, we had to remove the NetCom box and analog filters with their support plate.
The switch is attached to the bottom of the tank with two sqares with one screw per square. Before our intervention, it was attached with 4 screws, but we decided to mount it with two screws since the two others are really difficult to access. This will help for future interventions.
We also changed the optic fiber between the Ethernet switch and the tank feedthrought. Actually it was the culprit of the issue.
We removed:

• Ethernet Switch: 1231.9g
• Optic fiber: 8.68g

We added:

• Ethernet Switch: 1228g
• Optic fiber: 7.95g

After closing the tank, Fabio and Piernicola worked on the bench balancing. They added one screw two balanced it properly.

Probably due to the blackout of March 1, the laser beam on laser bench was slighly misaligned with the PMC cavity, which worsens the laser power stabilization loop and add some noise on the laser power noise.

On wednesday March 4 around 15:10 UTC, we re-aligned the incoming beam of the cavity by adjusting the orientation of one of the mirrors before, LB_M12.

The 2 figures show the time series and the spectral desities of the power stabilisation photodiodes. After realigning the PMC cavity, its output power increased a bit, as seen in the time plot. And the laser power noise was reduced, especially at low frequency below 2Hz, as shown in the FFT plot.

As seen in the FFT plot with the signal taken before the blackout. The current noise level is slighly higher then before the blackout, and some "sidebands" at 1 Hz around the 50 Hz signal appeared. This may be caused by the eletric system, but we don't know yet their origin.