Today, we proceeded with the alignment of the CO₂ actuators with the NI RH, based on the measurements performed yesterday.

At the beginning, we encountered some problems with the picomotor control interface. After discussing the issue with Giulio and Franco, we understood that the problem was related to the incompatibility of the old interface with the new operating systems. To bypass the problem, we used CTRL1 to control the picomotors. However, the picomotors can also be controlled directly from the VPM, which is the solution we will use next time.

The ITF was set in NI SB, with the SR aligned and the B5 drift control disengaged.

8:47 UTC: HWS data acquisition started (20260902T1047)
8:50 UTC: NI CH ON (wavefront 6)
8.54 UTC: NI CH OFF (Wavefront 11)

An example of the measured wavefront is shown in Fig. 2.

STEP 1 – TY adjustment
We moved the CO₂ actuators by 1 cm (5556 steps) backward in TY.
9:04 UTC: NI CH ON (wavefront 28)
9:12 UTC: NI CH OFF (wavefront 45)

STEP 2 – TX adjustment
We moved the CO₂ actuators by 1.4 cm (7906 steps) backward in TX.
10:00 UTC: NI CH ON (wavefront 132)
10:07 UTC: NI CH OFF (wavefront 145)

STEP 3 – TX fine adjustment
We moved the CO₂ actuators by an additional 0.5 cm (2800 steps) backward in TX.
10:43 UTC: NI CH ON (wavefront 211)
10:54 UTC: NI CH OFF (wavefront 229)

STEP 4 – TY fine adjustment
We moved the CO₂ actuators by 0.5 cm (1000 steps) forward in TY to fine-tune the horizontal position, since the two directions are slightly coupled when moving in TX.
11:14 UTC: NI CH ON (wavefront 267)
11:25 UTC: NI CH OFF (wavefront 288)

Through these successive adjustments, we progressively superimposed the CH center on the RH center. Figure 3 shows the RH, together with the CH in its initial and final positions.

The measurements were completed at 11:25 UTC.

The CO₂ actuators are now centered on the NI mirror within approximately 0.5 cm.

After that, we switched off the HWS-DET SLED to proceed with the HWS-INJ activities.

ITF found in LOCKED_ARMS_IR, COMMISSIONING mode

7:00 UTC ITF in SINGLE_BOUNCE_NI with B5 beam drift open and SR ALIGNED after a cross alignment and reaching LOCKED_ARMS_BEAT_DRMI_1F for a few seconds

7:30 UTC CO2 benches check (Corubolo, Nardecchia)

12:00 UTC ITF in LOCKED_ARMS_IR with B5 beam drift open

13:18 UTC NI etalon loop set to 19.57, 20000s ramp (Mantovani, operator)

13:23 UTC INJ lab ventilation set to Portata Nominale (operator)

13:30 UTC EIB camera placement, ITF in DOWN state, ITF_LOCK and INJ_MAIN paused (Gosselin, Lagabbe, Spinicelli)

13:35 UTC TCS Auxiliary Cooling System Chiller Setpoint changed to 17.8 °C (operator)

The VIM page with sideband gains has been reporting surprisingly low sideband gains, with a gain of at most 34 for the 6MHz sideband when the CITF is locked.

Figure 1 looks at the sideband magnitude measured at different times. In blue at the beginning of O4 in May 2024, in green in March 2026 during the squeezing injection work, in red on August 11 after the mirror and CP replacement, and in purple on August 28. 

After the mirror replacement the 6MHz sideband magnitude looks to be ~15% higher than before the replacement. The 56MHz sideband gain has been more varying after the replacement, probably depending on the quality of the SR alignment, and has been at least the same and up to 30% higher than before the replacement.

Figure 2 shows the  6MHz sideband power measured by the B4 phase camera in CITF, and Figure 3 in single bounce. Using the formula from the OptChar paper G_SB = T_PR * T_BS^2 * R_IM * P_B4_CITF / P_B4_SINGLE_BOUNCE, the sideband gain is around 53 for the LSB, and around 51 for the USB. Which is still far away from the value of a perfect interferometer around 75, but better than it used to be. 

Figure 4. Looking at brief locks from Sep 1, the 6MHz sideband gain may be as high as 60.

The simulation of the PR CHROCC imperfection where showing that the maximum theoreticaly possible gain for the 6MHz gain is 68, given the simulated PR CHROCC imperfections VIR-0567C-22.

Romain checked yesterday's data (69675) and pointed out that the B5 drift control was engaged during the measurement. Unfortunately, this makes the measurement unreliable.

Therefore, today we needed to repeat the measurement performed yesterday.

The ITF was prepared for the measurements in the following configuration: NI in single bounce, B5 drift control disengaged, SR aligned, and the additional loop on the NI MIR switched on.

The HWS-DET illumination is shown in Fig. 1, with the SLED voltage set to 1.45 V.

14.13 UTC: HWS ACQUISITION START (20260901T1613)

14.24 UTC: NI RH ON at around 15 W (V=23 V, WAVEFRONT 7)

16.07 UTC: NI RH OFF  (WAVEFRONT 56)

The RH signature shows up clearly in the HWS map (Fig. 2).

Unfortunately, after switching off the RH at around 16:40 UTC, MATLAB crashed and the HWS data acquisition was interrupted.

At this point, we started a new measurement using the same reference wavefronts as in the previous measurement.

16.50 UTC: HWS data acquisition started again (20260901T1850), using the same reference images of the previous data acquisition run

16.57 UTC: NI CH ON at high power (WAVEFRONT 2)

18.01 UTC: NI CH OFF (WAVEFRONT 34)
The CH signature shows up clearly in the HWS map (Fig. 3).
Using both measurements, we identified the maximum and minimum OPL generated by the RH and CH, respectively, and determined the corresponding coordinates, as reported in the table below.

Thus, on the mirror, the displacement between the CH and RH  (or TM) centers is:
ΔX =  (15 ± 4) mm 

ΔY = (17 ± 4) mm 

So, we need to move the CO₂ actuators by approximately 1.7 cm downwards and 1.5 cm leftwards.
In Fig. 3, some control signals recorded during the measurement are shown. We did not notice anything unusual, but it would be useful if the experts could have a look and confirm that everything is fine.

Tomorrow, we will switch the CH on again and align it with the center of the RH.

NB: Manuel disengaged the NI MIR loop, and Fabio relocked the arms.

As mentioned by Romain Gouaty during the daily meeting the SDB1 bench angle has been changing during this measurement, due to the B5 drift control loop which was closed and trying to follow the beam

Figure 1-5 show a few different examples of the B1p and B5 beam shape during the measurement, both of them change shape and size. I expect that this is due to the thermal lens in the NI CP detuning the detection telescope, either by just moving the camera position with regard to the beam waist, and the beam being astigmatic. Or more likely, because the beam stops being collimated at the input of the parabolic telescope, and parabolic telescopes become more abberrated when used for converging or diverging beams.

Especially on figure 5 the beam stops being round. For the B5 beam the cross beam shape is normal, as the B5 pick-off is highly polarized by two mirrors actiing as polarizers before the B5 camera, so most of the beam on the camera is in P-polarization and shows the cross pattern of the injection Faraday depolarization. 

Following a beam which changes shape with the B5 quadrant is not a right choice, and the better solution is to turn of the drift control. Note that today when the drift control was turned off the beam moved by ~20urad, and turning off the floating set points, and adjusting the fixed set points to restore the bench orientation was needed.

To investigate the excess noise in the vertical LVDTs, I performed a brute-force correlation analysis with BruCo, using all ENV and INF channels over the GPS interval identified in #69615.

The results, available at this link, show that the seismometers and accelerometers around the EIB are correlated with the excess noise below 10 Hz. However, these correlations may simply witness the excess motion measured by the LVDTs, rather than provide information about its origin. No other noteworthy correlations were identified.

ITF found in COMMISSIONING Mode and LOCKED_ARMS_IR State.
All times are UTC.

06:00 MAINTENANCE begin.
06:55 - 06:57 DET: OMC 1st, Lock attempt interrupted due to INJ unlock, B1 shutter closed for safety (operator, see attachment #1).
07:04 - 07:09 DET: OMC 2nd Lock attempt interrupted due to OMC temperture jump (operator, see attachment #1).
07:12 - 07:16 DET: OMC 3nd Lock attempt interrupted due to OMC temperture jump (operator, see attachment #1). OMC Lock skipped for the moment, experts informed.
07:27 - 07:48 DET: OMC Scan (operator, see attachment #2).
07:48 - 07:55 DET: OMC B1/B1_PD3 demodulation phase adjusted, OMC Lock performed, B1_PD3 photodiode offset adjusted (Gouaty, #69677). 
08:16 - 08:26 TCS: Thermal Camera Reference (operator).
08:45 - 08:56 TCS: Power Checks (operator).
10:00 MAINTENANCE Ended.
13:52 TCS: CO2 Bench Checks with HWS begin (Nardecchia, Corubolo).

ITF left in COMMISSIONING Mode, SINGLE_BOUNCE_NI State, SDB1_LC B5 drift control disabled and SR aligned.

Sub-system reports:
DET
SDB1_Quadrants offsets kept to the SINGLE_BOUNCE_NI ones to allow TCS work with DET HWS.

TCS
CO2 Power Checks at the pickoff (TCS__CO2_POWER_CH_PICKOFF):

Figure 1. The adjustment today has essentially reversed the adjustment I had done on Sunday evening. When the interferometer was DOWN for a few hours on Sunday afternoon the offset has increased over a few hours. Once I did the offset adjustment, and relocked the arm the offset has decayed back on a time scale of 12 hours. Which made reversing the Sunday adjustment necessary. 

Figure 2. The offset on B1 PD3 is closly following the temperature changes on the bench, which is what one could expect. And the adjustment on Sunday happened to be at the peak of the temperature excursion following the issues with SDB2 on Sunday afternoon. https://logbook.virgo-gw.eu/virgo/?r=69669

This morning, the OMC was not locking due to a mistuning of the OMC error signal demodulation phase, which was found to be wrong by ~90 deg.

The demodulation phase of B1_PD3 was adjusted to 3.4 rad (previous value was 1.85 rad). After reloading the external configuration at 07h45m54 utc, the OMC was able to lock on the TEM00 at first attempt.

Assuming that the demodulation phase for the B1_PD2 photodiode would be affected in the same way, we also adjusted the B1 demodulation phase from -0.6 rad to 0.97 rad. The new demodulation phases have been recorded in the main configuration file of process SDB1_OMC.

We also noticed that the offset of the B1_PD3 photodiode was quite large. The offset was retuned and we reloaded the configuration of SDB2_dbox_bench at 08h05m03-UTC (see attached figure).

This afternoon, we performed several checks before starting the HWS-DET acquisition with the NI RH ON.

As a first step, we checked the HWS-DET acquisition and encountered an issue with the MATLAB version called by the Python code of the acquisition software. Giulio solved the problem by updating the acquisition code to make it compatible with the  MATLAB version 2023.

Now the command to launch the acquisition is:  

./hwsAna2022_R2023a.py -d/r/l DET 

In parallel, Fabio went to the Central Building to switch on the power supply of the NI and PR RHs.

At this point, we prepared the ITF for the measurement. After being locked in CITF with the additional loop on the NI MIR engaged by Paolo, the ITF was set in NI single bounce.

The HWS-DET illumination is shown in fig. 1. The voltage of the SLED has been settled to 1.45 V.

14.41 UTC: HWS ACQUISITION START (20260831T1641)

14.58 UTC: NI RH ON at around 10 W (V=19 V)

16.49 UTC: NI RH OFF  (WAVEFRONT #42)

The RH signal was clearly visible in the HWS map (see Fig. 2).

The HWS beam appears to be displaced with respect to the center of the mirror by approximately 1 cm and 2 cm along the two directions..

To verify the alignment of the NI CO₂ actuators, I switched on the NI CH at 17.12 UTC.

An example of the wavefront map with CH ON is shown in fig. 3. The CO₂ actuators and the RH appear to be well aligned in the horizontal direction, while the CH appears to be slightly lower than the center of the mirror in the vertical direction. However, I would like to repeat the measurement with the CH, since this measurement was performed after several hours in SB.

At the end of the measurement, I closed the NI CH flip mirror (19.38 UTC).

Paolo will disengage the additional loop later this evening.

The North arm will most likely need some time before it can be relocked.
 

Below the list of the activities communicated in control room:

TCS: det hartman sensor re-installation (#69673);
TCS: NI alignment check with hartman det sensor, in progress... 

Air Conditioning
from 9:50UTC to 10:20UTC I set the detection area air conditioning system in "Portata Nominale" to allow the work on det hartman sensonr;

In order to start the check the NI HWS alignment with the NI RH of this afternoon,  we put back the HWS-DET camera in place of the CCD.  

The same plot related to 2 events that occurred on 2026-08-20-04h58m40-UTC and on  2026-08-20-08h51m30-UTC :

• For each of these events, the timing_error signal of the RightUp and RightDown DBoxes were still correctly collected 

As already experimented  2 times during the week from 17-22 August, the  SDB2_DBOX_LeftUp DBox was found unreachable in the Tolm network since 2026-08-30-14h22m05

 Its have been recovered by performing 

• an OFF/ON using  the  SDB2_POWERSUPPLY  server 
• and a full reconfiguration of  the SDB2 bench DBoxes 
• Operations performed betxeeen 2026-08-30-18h32m45-UTC and  2026-08-30-18h57m14-UTC

The problem is not understood. For the time being

• all the SDB2 suspension controls have been left open
• the ITF_LOCK Metatron node put in DOWN

The attached plot shows  the trend of the DBOXes' timing error channels and their  12V power supply channels before the event, during the event, and after the DBoxes reconfiguration

DET_MAIN was stuck in UNKNOWN state because of a large offset on B1 PD3. After adjusting the offset around 19:45 UTC, I could put back DET_MAIN into the SHUTTER_CLOSED state. And then lock the arms using ITF_LOCK. SDB2 is not used for locked arms, so it should be ok to keep the arms locked even if SDB2 is not controlled.

ITF found in DOWN State and COMMISSIONING Mode.
All times are UTC.
05:12 - 09:00 DAQ: EPRB, SIB2, ALS DAC firmware update (Masserot, #69668).
09:26 - 10:38 PSTAB 50Hz harmanics feed-forward preparation, turned on at 10:18, and it will be turned of at the end of the day (Was, #69666).
10:37 CITF relocked only at 1F stage, the handoff to LOCKED_ARMS_BEAT_DRMI_3F caused several unlocks.
ITF left in COMMISSIONING Mode and LOCKED_ARMS_IR State.
 

We continued to deploy the DAC1955 v3r3 firmware on the DAC1955 boards by completing the SPRB part and running it on the SIB2 and ALS subsystems.

• SPRB_rtpc : DAC1955 firmware completion: 1 DAC1955 board updated, the one use for SBE and Phase camera
  • Tolm output data flow reduced from 12.6MB/s to 2.56MB/s  
• SIB2_rtpc : the 4 DAC1955 boards are updated
  • Tolm output data flow reduced from 16.78MB/s to  3.43MB/s
• ALS: the 3 DAC1955 boards are updated 
  • ALS_NEB_rtpc: Tolm output data flow reduced from 4.2MB/s to  0.34MB/s
  • ALS_WEB_rtpc: Tolm output data flow reduced from 4.2MB/s to  0.31MB/s
  • ALS_CEB_rtpc : Tolm output data flow reduced from 4.2MB/s to  0.53MB/s

Operations performed between 2026-08-28-05h30m03-UTC and 2026-08-28-09h12m26-UTC

• all the loops were opened during the time of the operations and successfully closed at the end
• At the end the ITF was relocked at LOCKED_ARM_BEATING  after the re-aligment of the ALS_CEB phototiodes used to acquire the NARM and WARM beating beams

Below the detailled list of the DAC1955 boards updated and the related ACL's server

SPRB :

• SPRB_SBE and EPRB_PC : 1 DAC1955 board
  • SPRB_DAC_SBE0 : DAC1955_SN004 - DBOX_SN025 - SPRB_dbox_rack : shared DAC1955 board
    • SPRB_SBE server: ch00-ch05 : 6 channels
    • EPRB_PC server  : ch06-ch07 : 2 channels
• We checked  that the Tolm packects are correctly received by the DAC board
• The SPRB_SBE loops were successufly closed after the update 

SIB2:

• SIB2_LC  and SIB2_SBE : 3 DAC1955 boards
  • SIB2_DAC_LC_LVDT_in : DAC1955_SN005 - DBOX_SN001 - SIB2_dbox_bench  
  • SIB2_DAC_LC_LVDT_out : DAC1955_SN015 - DBOX_SN020 - SIB2_dbox_rack 
  • SIB2_DAC_SBE0 : DAC1955_SN009 - DBOX_SN047 - SIB2_dbox_rack
  • We checked  that the Tolm packects are correctly received by the DAC boards
  • The SIB2_LC and SIB2_SBE loops were successfully closed after the upgrade
• SIB2_Quadrants :  1 DAC1955 board
  • SIB2_DAC_galvo : DAC1955_SN137 : DBOX_SN101 - SIB2_dbox_bench
  • We checked  that the Tolm packects are correctly received by the DAC board

ALS

• ALS_NEB_BPC: 1 DAC1955 board
  • NEB_DAC_ALS0 :  DAC1955_SN062  : DBOX_SN066 - NEB_ALS_dbox
  • We checked  that the Tolm packects are correctly received by the DAC board
  • The IR PSTAB loop was successfully closed after the upgrade
• ALS_WEB_BPC: 1 DAC1955 board
  • WEB_DAC_ALS0 : DAC1955_SN002 : DBOX_SN050 - WEB_ALS_dbox
  • We checked  that the Tolm packects are correctly received by the DAC board
  • The IR PSTAB loop was successfully closed after the upgrade
• ALS_CEB_BPC and LNFS_RAMSs :  1 DAC1955 board
  • CEB_DAC_ALS : DAC1955_SN145 : DBOX_SN086 - CEB_ALS_dbox : shared DAC1955 board
    • ALS_CEB_BPC : ch00-ch03 : 4 channels 
    • LNFS_RAMs     : ch04-ch07 : 4 channels
  • We checked  that the Tolm packects are correctly received by the DAC board
  • The PZT NARM and WARM loops were successfully used to increase the NARM_DC and WARM_DC signals
    • Operations performed between 2026-08-28-09h10m43-UTC and 2026-08-28-09h12m26-UTC  

After the issue with the EIB actuators of August 14th  and the several interventions to mitigate the problem, the green beam on the EIB got a bit misaligned, especially on the North arm path (Fig. 1). As a consequence, the yesterday attempt to lock the arms on the beating did fail. 

In the afternoon of yesterday,  we used the picomotors on EIB to realign both path (fig2). For the time being, we didn't realign the ALS_CEB_BPC, as we want to perform it with the CEB_GREEN off (to mainly align on the ARM signals), but for the moment is not possible to use the flip mirror without unlocking INJ.

To be noted that at first attempt, the picomotor were not responding, even with a restart of the server. We needed to physically unplug and replug their power supply in the IER to get them working. Being the second time in few weeks that this happens, we will investigate wheter it is due to an hardware problem. 

This morning I have corrected the logic error at 10:16 UTC.

Figure 1. Shows the safety working properly, the FF corrections visible in INJ_PSTAB_NOISE and the FF tracking loop start at 10:17:30 UTC, 20 seconds after the RFC locks, despite the ENABLE flag being activated since at least 10:17 UTC.

Enabled also the 250Hz FF, and leaving it on for the day to see if any issues arises over several hours. I will disable the PSTAB FF loop at the end of the day as a precaution for the weekend.

In addition to the two action reported, the "energy safe" option has been selected yesterday too (see fig. 1). 

Other than the usual 1Hz comb noise,  present with those chiller when the safe mode is not selected, we could see a sawtooth oscillation on T of the chiller and the neoVAN diodes, with a period of about 11min (see fig. 2).  
The oscillation went away as soon as we changed the operation mode.

Yesterday evening I have tried to add a safety to the feed-forward to automatically turn it off when RFC_TRA_DC goes below 2V (unlocks). 

Figure 1 shows the result just after restarting the ISYSnoise process with the changes. The FF correction (eventually dominating the RMS of INJ_PSTAB_NOISE) starts immediately with a ramp of 20 seconds, instead of starting with a delay of 20 seconds after the RFC locks. I need to correct the logic of the safety.

---------

16:40 UTC restarted ISYSnoise to add a check that disables the 50Hz
harmonic FF when the RFC is not locked. Not fully certain if it works
as the timer is 20s while the 50Hz FF loop started acting only 10s
after the RFC locked.

17:01 UTC (5min) 250Hz FF enabled and stable

17:16 UTC disabling 50Hz and 250Hz FF
 

ITF found in COMMISSIONING Mode and DOWN state, with MISALIGNED_ALL_BUT_NI state on ARMS_LOCK node (equal to SINGLE_BOUNCE_NI state from ITF_LOCK).

Planned activities:
- First check on DET HWS and SLED beam (Lumaca, Corubolo), concluded at 11:10 UTC.
- Opening of Cryo Valves (VAC team), performed at 08:49 UTC.
- New position for GRAS microphone on Injection Tower, concluded at 09:15 UTC.
- Spare Neovan Chiller tuning in EERoom (Lagabbe, Zaza), performed at 12:00 UTC.

In order to allow the TCS activity:
- I set UTA DET in Portata Nominale.
- I recovered all metarton nodes in standard state.
- Thanks to Ruggi we realigned and relocked cavities.
- I recovered the SDB2 vertical position via stepping motors and close SDB2_SBE loop.
- Thanks to Gouaty we recovered the SDB2 position and close LC loops.
- I set ITF in SINGLE_BOUNCE_NI with SR manually aligned.
- Upon concluded the activity (11:10 UTC) I set again UTA DET in Portata Ridotta and re-misaligned SR.

I tried to move on with the lock acquisition up to ACQUIRE_DRMI in order to perform the usual cross-alignment, but unfortunately ITF unlocked at LOCKING_ARMS_BEATING while Engaging boost filter #1. Investigation in progress on EIB (Spinicelli).

ITF now in standard state in LOCKED_ARMS_IR.