Today we tried to recovery a stable lock in CARM null 1f in order to proceed with the TCS tuning, however we encountered some troubles during the shift.

We weren't able to find a stable lock up to carm null , unlocking most of the times at CARM step 3/3 (or randomly before), so right before carm null 3F.

At first we didn't find any clear explanation to the several unlocks. We tried to tune the sevaral phases and gains in order to make more robusts the steps, with no success, without even being able to engage the Diffp loop in drift control. At the end we found a correlation to a misfunctioning of the NI Etalon loop.

After the adjustement of the setpoint performed in the beginning of the afternoon (https://logbook.virgo-gw.eu/virgo/?r=69752) we noticed that the loop was still not properly working since it was not converging correctly to the setpoint as the temperature was still increasing above it, see fig.1.

A correlation was found with the Etalon misbehaviour and a change in the sidebands powers alonf the shift, see fig.2.

Expert was notified about the issue. Investigation will be performed to understand if the misfunctioning is at the level of the hardware or at the level of the control loop logic.

ITF found in COMMISSIONING Mode and LOCKED_CARM_MC_IR State, with activity on CARM_NULL/TCS DAS tuning ongoing. 
Activity concluded around 19:30 UTC.
ITF left in COMMISSIONING Mode and LOCKED_ARMS_IR State.
 

This morning we went to EER to investigate the extra noise on the EIB LVDT. The idea was to check the 10 kHz generator used for the modulation/demodulation.
However, when arriving, we noticed that the noise had actually been lower since the 26th of August (Figure 1).
On that day, the chiller of the Neovan electronics, situated right next to the rack of the EIB electronics, stopped working at 14:00 UTC. We went to EER starting from 14:15, but the noise was reduced at 14:40...
Given these new elements, we suspected that some of the cables of the EIB electronics could be loose and sensitive to being touched.
We checked them, and some of them were indeed quite loose. Touching them was introducing glitches in the control loop. We tightened them. It still seems quite sensitive.

Anyway, the noise seems to be similar to the level it was before the 14th of August (Figure 2: blue now, purple 14/08 before the noise appeared, red 17/08 with the extra noise, green on 27/08). It is worth noting that the horizontal LVDT now seems to be higher. It is not easy to draw clear conclusions since these signals also depend on the seismic activity. Also, the noise reduction seen in the RMS on the 26th is not so clear in the FFT.
We will keep monitoring the situation and will speak with Henk Jan about whether or not we should undo the changes he made to the control filters on the 21st of August.

All these tests were done with the injection down and the flip mirror at the output of the PMC flipped up.
When relocking the injection with the same BPC corrections, the beam appeared to be quite far away from the IMC cavity, particularly horizontally.
We suspected that the EIB position was different from the morning. This seems to be confirmed by the fact that the BPL corrections have changed, the beam seen by IBJM is in a different position and the corrections of the EIB actuators are different. This is the case even though the only EIB position that changed was the Tx position of the EIB, which was 1 µrad away from this morning (Figure 3).
We are quite surprised by this. It might be evidence that something is wrong with the position read by the LVDT (?).

6:00 UTC ITF found in COMMISSIONING mode and LOCKED_ARMS_IR state and set to MAINTENANCE mode and DOWN state

6:30 UTC DET_MAIN node set to SHUTTER_CLOSED and PAUSE, SDB2 angular and position loops open, DET photodiodes Vbias disabled for DET EER faulty power supply replacement (9 swapped with 31). At the end of the operation the offset of the B1_PD3 was large and was corrected by Romain. Metatron put back in standard state at 11:30 UTC #69748 #69754 (Berni, Gouaty, Masserot, operator)

7:00 UTC WI optical levers cabling check and Removal of WI MIR PSD power switch #69749 (Boldrini, Cavalieri, Majorana, Nocera)

8:20 UTC Reset of 10 kHz modulation for EIB LVDTs (Gosselin, Lagabbe)

10:09 UTC NI mirror temperature increase: NI etalon set to 19.78 ramp 1 #69752 (Bersanetti, Mantovani, Spinicelli, operator)

Other operations carried out during maintenance:

• Nitrogen refill (Vac group)
• CB cleaning (external company)
• TCS chillers refill (Menzione)
• TCS thermal cameras checks and power checks (operator)
• Installation of cameras in CEB (Berni, Kraja)
• DAQ room, INJ EER, DET fiber length checks (Di Biase, Kraja)
• Fire estinguishers inspection in CEB (Fabozzi)

OMC scan/NI single bounce configuration skipped due to other operations ongoing (DET, DAQ, INJ)

12:00 UTC ITF in COMMISSIONING mode and LOCKED_ARMS_IR state

After the morning operations the DET_MAIN node was found stuck and unable to reach SHUTTER_CLOSED.

First we checked that the shutter was indeed closed by looking at the image of the camera B1s and increasing the integration time at maximum: no light was visible.

We noticed that the offset on the B1_PD3 photodiode was large (about 0.45 uW). Therefore we corrected it in the configuration of SDB2_dbox_bench (reloaded at 11h39 utc).

After the correction of the offset the standard state of DET_MAIN could be recovered by requesting the following states:

* FORCE_CHECK_CLOSED

* SHUTTER_CLOSED

For comparison, here we plot the B1p beam shape in CITF respectively  without any TCS compensation, with only DAS (after ~1h) and with both DAS and CH.

The NI etalon loop was not working properly due to a too low setpoint (we could not raise to do not interfere with the commissioning activities), for unknown reasons the temperature of NI increased, see figure 1.

We decided to open the loop (to discharge the corrections) and re-closed with higher set point.

Francesco replaced the Hameg_SN09 with the Hameg_SN31(box containing the Hameg power supply, rear and front wiring) used by the LeftUp and LeftDown  DAQ boxes

After this operation,

• the SDB2_PowerSupply server configuration has been updated accordly and successfully restarted
• the SDB2 DAQ boxes have been successfully reconfigured 
• the Photodiodes and Cameras have been set to their expected state
• The DET_Img_CEB server, used to acquire the SDB2 cameras, have been  restarted 
• and the SDB2_LC and the SDB2_SBE loops were successfully closed 

The attached plot shows  the trend related to SDB2 DAQ boxes power supplies

The switch box has been restored, the fault was simply a cable not well connected.

The behaviour of the MIR signals is identical to what it was before the intervention (fig.1 before, fig.2 after). We also restored the damper gain to its previous value.

The glitches observed on MIR PSDF in May (fig.3, 69083) are still there, although their shape is slightly different.

We turned off and removed the switch box between the MIR PSD and the respective power supply on the WI payload.

The MIR signals are now offline, and the damper's gain was set to 0 beforehand.

We will try to repair the switch box and reinstall it before the end of today's maintenance.

The planned activty of the shift was:  TCS CARM_NULL_1F recovery ; it went on without major issues.

Activity concluded at 19:00 UTC; ITF left in locked arms IR.

The goal of this shift was to recover CARM_NULL_1F.

During the afternoon the ITF slowly continued to thermalize after the TCS actuators were enabled, causing the sidebands to rise in power at a steady rate that only started forming a plateau around 16:00 UTC (Fig.1).

This forced a continuous back and forth to adjust gains and phases, following this moving target, until the thermalization process stabilized.

Towards the end of our shift we managed to reach CARM_NULL_1F but could not stabilize this state, as a 11 Hz oscillation, slowly but steadily rising, eventually breakes to lock. The main culprit seems to be SRCL gain being too high, with the oscillation being wide enough to overwhelm the UGF servos, preventing them to adjust the gains. This oscillation is witness by a vast number of longitudinal and angular loops, making diagnosis more difficult.

Overall, the demodulation phases are adequate in 3F and good enough in 1F to allow the transition, but we could not complete their fine tuning before the end of the shift.

A fourth event occurred the 2026-09-13-11h28m55-UTC and was promplty recovered .

This morning, we first checked that the CO2 actuator powers were still consistent with the values set last week, based on the OSCAR simulations and summarized in the table below: 

Only a small adjustment of the NI CH power was needed, probably due to the recent interventions on the cooling system. At the end of the check, all the CO2 flip mirrors were closed again. 

A first attempt to reach CARM NULL was performed around 08:10 UTC, but it was not successful. No clear evidence of PA was observed on the ITM thermal cameras. 

We therefore decided to return to CITF and proceed with the switching ON of the CO2 actuators. CITF 1F was reached at around 08:44 UTC, with the following initial sideband levels:

• 112 MHz: 0.027 mW

• 12 MHz: 0.051 mW

At 08:45 UTC, the DAS flip mirrors were opened, with the powers reported in the table above. The evolution of the sideband levels was then monitored for almost two hours. A general worsening was expected with the DAS actuators ON alone. 

After about one hour, at 09:55 UTC, the 56 MHz and 6 MHz sideband levels had decreased by approximately 30% and 20%, respectively. We agreed to manually unlock the interferometer at 10:10 UTC. 

The ITF returned to CITF 1F at 10:20 UTC, with the following sideband levels:

• 112 MHz: 0.0195 mW (-27%)

• 12 MHz: 0.0355 mW (-30%)

The levels were then quite stable. The trend during this first period is shown in Figure 1. 

At 10:34 UTC, the CH flip mirrors were opened, again with the powers reported in the table above. The sideband levels increased almost immediately. Already after about 20 minutes, at 10:55 UTC, they had nearly recovered their initial values. 

After the lunch break, some adjustment of the PR angular loop gain was needed to allow the ITF to lock again in CITF 1F, which was achieved at around 12:05 UTC. The sideband levels then reached: 

• 112 MHz: 0.0305 mW (+12%)

• 12 MHz: 0.0544 mW (+7%)

The trend during this second period is shown in Figure 2.

Just before the Daily Meeting, the first attempts to reach CARM NULL started.

The activity continued with the afternoon shift.

ITF found in COMMISSIONING Mode and LOCKED_ARMS_IR State,
All times are UTC.
07:06 Start of commissioning activity - Turn on DAS/CH in CITF (Lumaca, Corubolo, Nardecchia, Bersanetti, Spinicelli).

The shift was dedicated to TCS activity with centra interferometer lock. Activity still ongoing.
ITF left in COMMISSIONING Mode and LCOKED_ARMS_BEAT_DRMI_1F State.

The only remaining ISC related explanation that I can think of to explain the large decrease in sidebands are large offset in PRCL or MICH.

Figure 1 shows an example of a lock acquisition on Friday. Around 15:24 UTC there is a transition where the B2 8MHz I signal becomes 3 times smaller, other B2 signals have also a step, and the SSFS line height in B2 DC decreases by a factor 4. But it has no incidence on the sideband recycling gain. This step behaves like a large improvement in PRCL offset, and thas not impact on the sideband gain, which would mean that a PRCL offset doesn't play a role in the sideband gain decrease.

On the other hand at 15:20:30 UTC there is another large transition. Where the sideband gains decreases, especially the 6MHz. At the same time the misbalance of the 56MHz sideband on B1p increases by a factor 3, and the 6Mhz power on B1p also increases by almost a factor 2. This misbalance then continues to increase over time, the B1p 6MHz power increases over time, and the sideband gain decreases. This could be explained by a very large offset on MICH, that then continues to increase over time. 

Figure 2, 3 and 4 shows phase camera images on B4 and B1p during the CARM null lock. The sidebands on B4 progressively move away from the position of the carrier on B4. And the shape of the 6MHz sideband, and 56MHz LSB becomes more and more like a doughnut, which would be a sign of a mismatch between the north and west short Michelson, which could mean one of the input mirrors absorbs much more than the other.

After adjusting the B1 PD3 offset the DET_MAIN checks of the slow shutter were successful and I could relock the arms. The offset adjustment will probably need to be undone in a few hours as the temperature of the SDB2 bench is slowly coming back up once it is back to be supplied in power. 

I ran an OSCAR simulation considering an input power of 12 W and an absorption of 0.3 ppm, as specified by LMA for the new mirrors. With these values, the absorbed power is about 20 mW.

In the absence of thermal effects (i.e. in the ideal case), the gains are about 74 and 51 for the 6 MHz and 56 MHz sidebands, respectively, assuming 1500 ppm losses in the recycling cavities.

No cold maps of the mirrors were included, except for the POP cold maps. I assumed PR and SR RoCs of 1430 m, RoCs of 1427.8 m and 1428.8 m for the new input mirrors, and RoCs of 1670 m for the end mirrors, corresponding to the expected value with the RHs on.

Including the OPL variation induced by 20 mW of absorbed power, shown in the attached figure, the 6 MHz and 56 MHz sideband gains decrease to about 29 and 22, respectively. The gains are calculated considering all modes, not only the TEM00.

To obtain a 6 MHz sideband gain of about 10 in the simulation, the assumed absorption needs to be increased by approximately a factor of 3, from 0.3 ppm to 0.9 ppm. Equivalently, keeping the absorption at 0.3 ppm, the same thermal load would correspond to an input power of about 36 W.

For the third time, the SDB2_DBOX_LeftUp became unreachable on the Tolm network at 2026-09-12-21h02m15-UTC

• its power supply remotely driven has been switched OFF/ON at 2026-09-13-05h56m45-UTC
  • this allows to recover the  SDB2_DBOX_LeftUp dbox  from the Tolm network 
• All the SDB2 DAQ boxes have been successfully reconfigured 
• Only the SDB2 LC loops closed  successfully
• DET_MAIN is undefined state  

Operations performed between  2026-09-13-05h56m37-UTC and 026-09-13-06h16m38-UTC

The attached plot shows the SDB2 DaqBoxes timing error signals, their  +/-12V  power supplies monitoriing channels and each DBOX external temperature sensors (the one of RightDown doesn't work)

Yesterday morning I found all the ALS photodiodes at NE giving strange values (see fig. 1). Looking back in time, it appears that right after the opening of most of the suspension guardians  on Thursday night, all the ALS photodiodes (CEB, NE, WE) went to 0 several times as a consequence of the frequent unlocks. However, at NE those values stucked at 0 at 22.20UTC and almost one hour later they went to negative values (fig. 2). Also the SOA stopped to work.

Investigating the electronics of the power supply, we find out that apparently there was a loose connector on the +24 DC distribution box that started to became a problem only on Thursday night for no apparent reason. 

 Repairing the connector solved the problem. The NE ALS signals are stable since the restart of the photodiodes and SOA.

Yesterday afternoon, I did a first check of the NI mirror during the short CARM NULL locks of yesterday, no PAs has been observed so far, but the focus point of the camera has to be better set next days. 

Moreover, profiting of some down period during the commissioning shift at the end of the afternoon, I installed a new thermocamera at the WI, at the small ZnSe viewport access. 

As usual, the camera stream is accessible only from devices connected to the EGO WiFi network, via the address : http://172.31.10.153:8080/. Data will be acquired next week. Both camera should be accessible at the same time.

In order to check if ISC actions could help in the survival of the CARM null 1f step we have checked and tuned:

- SSFS phase and gain (tuned)

- PR tx and ty phase 

- B2 8MHz (input beam alignment) 

- SR alignment behavior

- DiffP set servo

None of these actions helped in reducing the drop of the sidebands

We tried also a lock acquisition with the SR misaligned -2urad in ty. No effect.

In view of the next commissioning activities, we set up a very basic (and temporary) check on the power reflected by the IMC (INJ_IMC_REFL_DC); this is done only in the IMC_RESTORED state of the INJ_MAIN node and, if failed, it will prevent moving forward to the lock acquisition if such power is out of a specific range (+- 50 mW around the current average, changes may still happen); this is to avoid bad lock attempts after unlocks following manual or automated changes of the input power, especially for lower power that may make the lock of the IMC itself less reliable.

A forced failure of the check has been tested, and the new cyclic decorator is now in operation.

06:00 UTC ITF found with the following loops open:

• top stage IB, OB, PR, SR, BS, NI, WI
• F7 BS, WI
• LC BS
• Position and angular SPRB, SDB2, SNEB, SEWB

ITF was put in DOWN with ITF_LOCK and INJ_MAIN nodes in pause.

I was able to close some of them but SIB1 and WI had too high a correction to hold. Manuel started working on the issue while I called Valerio (work in progress), since we noticed that many stages of different suspensions were close to saturation and needed to be moved with motors.

SBEs closed.

08:15 UTC I changed the TCS Aux cooling chiller setpoint from 17 to 16.1. Heating loop setpoints: WI 17.4, NI 17.2. CO2 CH powers are back to before adding glycol.

10:00 UTC ALS NE malfunction assessment: L1 power supply not working (Cavalieri, Spinicelli)

12:00 UTC ITF in LOCKED_ARMS_IR