The afternoon and the evening were spent working on Lock recovery up to STEP 3 #69724 (Bersanetti, Spincelli)

Commissioning activity ended at 19:30 UTC

21:00 UTC ITF left in LOCKED_ARMS_IR state and COMMISSIONING mode

Guard Tour

18.35 UTC

After the replacement of the LNFSs to the configuration that was in use last Monday afternoon, we reverted the automation configuration files to the svn snapshot in use at the time , in order to have a usable starting point.

We then proceeded to examine all steps of the lock acquisition from DRMI_1F onwards. We did notice some changes also at that stage, in terms of gains and demodulation phases. As usual, the 3F step was the most impacted.

Then we moved to the CARM/DARM handoffs to the IR, and the following STEP1/2/3 states of the CARM offset reduction, which had to be tuned more heavily.

We consider the recovery relatively reliable up to STEP3, with the following observations:

• MICH is apparently the loop giving more trouble in terms of stability and unlocks; it is also the one that easily gets to higher corrections (also in quiet times), hence the first one to lose control
• PRCL shows downgoing trends at each lock (in terms of UGF) that can be compensated up to a point with the loop gain; the situation is the same in subsequent locks;
• the engagement of DARM back on the IR is statistically not robust, although the loop configuration looks ok; tomorrow we should check better is something is not working of if the weather conditions had some impact (although they were not particularly bad);
• DIFFp has not been checked, and it is now disabled in STEP3 as we wanted not too many things moving at the same time.

The problem of not displaying correctly channels at different sampling frequencies (specifically when a 1 Hz channel is involved) is still present; dataDisplay v11r4 doesn't crash anymore but the visualization still has issues.

This plot , and its zoom,  shows the demodulated signals related to the LNFS generator and the EOM monitoring:

• the  *_raw_dFreq channel is the derivative of phase of the demodulated channel
• Usually the difference between the *_dFreq_min and *_dFreq_max is tiny 
• but around  2026-09-08-18h10m_UTC the first time for a short period  the frequency became different and noisy
  • the *_dFreq red cuves are the *_dFreq  signals low-pass filtered at 300Hz
• and around the 2026-09-08-18h16m_UTC ,the frequency difference and the  noise reappered  to remain :
  • the *_raw_dFreq signal is the derivative of the phase computed with the outputs of the demodulation board
  • the *_phi signal is the phase after the rotation using the LNFS demodulated channels and the *_dFreq the derivative of this phase
  • One can see that the noise is well present on the *_raw_dFreq of  the SIB2_RFC_PD1_6MHz and of the INJ_EAB_EOM_TRA_6MHz an it s not removed by the LNFS rotation 

The last plot shows the LNFS phase noise for the 6Mz and the 56MHz for according the LNFS devce used 

I have calculated the mismatch and throughput losses before and after the intervention.

INJ throughput losses on 07/09 (08:51:40 UTC):

INJ throughput losses on 08/09 (15:02:00 UTC):

Comparing both measurements, we have overall throughput losses increasing of less than 1% while the mismatch increased of roughly 3% after the power decrease. 

In addition to this change of LNFS devices, we had to change also the Lnfs100 server to take into account that we now need to remotely control only one LNFS. In particular, we reverted the python scritp PyLnfs100.py to the version used before the addition of the 81Mhz sideband (back in 2022). 

The server has been restarted and running without troubles since yesterday afternoon.

R. Cavalieri, F. Nocera, P. Spinicelli

Brief recap on recent events and current status concerning our sideband generators a.k.a. LNFS (Spectradynamics' LNFS-100).

We have purchased a total of four identical 3-output synthesizers over the years (starting in 2011) and we have been using two of them at the same time to generate our 4 sideband frequencies for a very long time (the entire O4 and even before that), namely 6, 8, and 56 MHz (Synth1) and 22 MHz (Synth2).

Following Feb 28th blackout, one of the two used syntesizers (Synth1) failed and had to be swapped with a spare (https://logbook.virgo-gw.eu/virgo/?r=68788), let's call it Synth3. The failure consisted in a problem at the power on which has not been observed ever since during the following months of tests and monitoring in the Lab.

Starting on Jul 11th, Synth3 showed "additional noise" on both 6 and 56 MHz (https://logbook.virgo-gw.eu/virgo/?r=69359) and, for that reason, was in turn swapped back with Synth1, on Jul 15th. No tests in the lab have been performed on Synth3 since to verify and understand whether or not the problem was reproducible.

Synth1 too proved to be noisier than one would have liked (https://logbook.virgo-gw.eu/virgo/?r=69656) and therefore the idea of putting in a different one in its place popped up. This was what we set out to do yesterday.

First attempt: we tried Synth3 which worked just fine when in "Local Mode" (i.e., when not controlled via RS-232) but did not when in "Remote Mode", behavior never seen so far. 
Second attempt saw the swap of Synth3 with Synth4, the one we use in our Lab setup to test and characerize RF devices before intergation in Virgo, which failed miserably since the device did not even turn on.

The solution found to allow commissioning activities to go on has been to use Synth2 to generate 6, 8, and 56 and accept temporarily a slightly degraded performance (which has no impact on the ITF performance) on the 22 MHz, now generated with Synth1.

For completeness, it is useful to remind the original (AdV) 22 MHz sideband does not need to have the low phase-noise performance offered by the LNFS-100 and used to be generated with a different, garden variety DDS; we could revert to that at any time if required. As it often happens, at some point in the past we tried out the solution with the LNFS for the 22 "for a test" and we never went back.
 

The first part of the shit was dedicated to the LNFS replacement.

After that the commissioning team worked at the CARM NULL recovery; activity concluded at around 19:00 UTC.

At 19:33 UTC the ITF was set in NI single bounce for 5 minutes.

ITF left in LOCKED ARMS IR.

SUSP

SR LC opened by the guardian at 16:00 UTC; properly closed.

After the LNFS replacement we started the recovery of the interferometer.

Despite the smooth operations of yesterday evening, today's shift was plagued by a variety of instabilities that always manifested differently: high gain oscillation of PR_TX, low gain oscilation of MICH and other similar effects that did not repeat sistematically at each lock.

At the end of the shift the 11.6 Hz vertical (bounce) motion of the PR was excited and prevented us from proceeding further with the recovery (Fig.1). We changed the damper gain to solve this issue (default: -0.017, changed between -0.014 to -0.025 to no avail).

The recovery will continue tomorrow.

The thresholds used for the definition of the QPD_B1s flag have been update in DetMoni. The checks on the B1s centering and the status of the galvo loop will be performed only after the state "SHUTTER OPEN".

Still digging in the data of July 28^th switch off, we further characterize acoustic noise entering the INJ room from outside. This investigation profits for the very low noise condition while the INJ HVAC was off.

A first point is the noise that enters from the Atrium. Figure 1 shows the effect of opening the Atrium door. There is a broadband noise increase of sound and vibration noise above 100Hz, particularly enhanced between 500 and 600 Hz (a factor 10) and the amplification of some narrow lines (105, 134 ... 290 ... 1010, 1048 Hz) which are indicated in Figure 2 with red markers.  For accelerometers see Figure 9. Inspecting this morning with Suzanne, we verified that the main (and seems only) sound source in the Atrium is the cooling fan of the ALS amplifier module (see Picture).   

The second  point is shown in Figure 4: note that structures between roughly 100 Hz and 1kHz in the acoustic and bench vibrations have large coherence with the IB tower vibration (sensor ENV_IB_ACC_X). We think this noise is related with the Turbo pump, as reported in these old tests (5 yrs ago.. and it seems yesterday!): elog 52500, this Figure  

Figure 4 also shows coherence with IB tower vibration in the region 1-3 kHz, that highligted in red circle. This is most probably noise from racks. Although we have not able to identify them: also the microphone placed on the platform near SIB1 tower does not show enhanced and coherent noise at these frequencies. And no evidence from EEroom microphone either.

Last point concerns the noise entering from EEroom: it is a triplet of acoustic lines (also with seismic counterpart) between 44 and 48 Hz  (Figure 5) and one important peak at 60Hz (Figure 6): all of them more intense in EEEroom mic.

The quadrant photodiode acquiring previously the B5_QD2 beam is now used to acquire the B1s_QD1 beam .

To be compliant with the new name of the beam, we  proceeded with the renaming of the B5_QD2 channels to B1s_QD1 channels .

The operations were performed between 2026-09-08-06h39m28-UTC and 2026-09-08-09h18m52-UTC 

Below the details of the operations performed:

• SDB2_dbox_bench server
  • DBox SN106 - demodulation mezzanine SN87
    • rename  as SDB2_DEMOD_B1s_QD1 instead of  SDB2_DEMOD_B5_QD2 previously
    • add the demodulation of the B1s_QD1 beam at  6MHz, 50MHz, 56MHz and 112MHz  for the 4 quadrant sectors
  • DBox SN007 - ADC2378 mezzanine SN43
    • renamed as  SDB2_ADC_B5_B1s_QD instead of SDB2_ADC_B5_QD previously
    • add the readout of the B1s_QD1_{H,V,SUM} channels  instead of the B5_QD2 ones
• SDB2_Tpro server and SDB2_ Fb server
  • Replace the old Tolm packets' name by the new ones
• SDB2_Quadrants  server 
  • Remove all the functionalities related to the B5_QD2 quadrants channels 
  • Add the last part of the demodulation of the B1s_QD1_{6,50,56,112}MHz channels
  • Add the B1s_QD1 galvo loops part
• SDB2_readout server
  • swap the B5_QD2 channels with the B1s_QD1 ones
• QPDMoni server
  • change the name associated to the interface ethmt7-2011 as B1s_QD1 instead of B5_QD2
• ASC_Acl server
  • the internal channels labelled B1s_QD1 are build using the SDB2_B1s_QD1 input channels
  • the internal channels labelled B1s_QD2 are build using the EDB_B1s_QD2 input channels
  • the B5_QD2 channels used in the TX_SENSING matrix and in the TY_SENSING matrix have been replaced by the B1s_QD1 respective channels
• Automation servers. ARMS_LOCK, DRMI_LOCK,
  • The related python config files have been updated by commenting the parts related to the SDB2_B5_QD2 quadrants 
• DetMoni server
  • all the parts related to the B5_QD2 quadrant photodiode have been commented
  • the monotoring part related to the B1s_QD1  quadrant photodiode have been added and remains to be tuned
  • A new flag B1s_QD1 has been in the DMS interface : the DMSserver server has been restarted to take in account this modification

6:00 UTC ITF found in LOCKED_ARMS_IR, COMMISSIONING, and set to MAINTENANCE.

Operations communicated to the control room:

• Nitrogen refill (VAC)
• Scheduled Tuesday cleaning (external company)
• TCS chillers refill (Ciardelli)
• Laser Lab measurements (Fiori, Tringali)
• Glycol addition to TCS AUX cooling system (Zaza)
• TCS cameras checks (Nardecchia, operator)
• TCS CH power checks (Lumaca)
• LNFS troubleshooting (Nocera, Spinicelli)
• SDB2_B5_QD2 renamed to B1s_QD1 in vpm and automation #69707 (Masserot, Bersanetti)
• Thermocamera Installation at NI #69708 (Melo, Spinicelli)

Taking advantage of the maintenance morning, between 09:20 and 09:38 UTC I set the CO2 DAS powers to the values identified by simulations as the starting working point for the interferometer with 12 W input power.

The CH powers were not set during the morning activity because glycol had just been added to the chillers (69706) while I was adjusting the DAS powers, making the measured powers unstable. Their setting was therefore postponed until after the daily meeting, when it was confirmed that the activity could proceed, and was completed at 12:25 UTC.

Since the CH powers had not yet fully stabilized, the reported values should be checked again when the CH flip mirrors need to be opened.

The resulting powers are reported below:

All flip mirrors were left CLOSED at the end of the activities.

Today we have installed the thermocamera Optris 640i on the HR face of the NI mirror, using the same support used for the infrared NI_cam. We adjusted the image focus and connected it to the online streaming, accessible only via EGO Wifi, at the address : http://172.31.10.192:8080/.

We also had to slightly adjust the focus of the NI_cam after touching the support to install the Optris thermocamera.

In the first part of the shift the injection team worked on the input power reduction (#69702) then the ITF lock recovery started; the work went on without any major problem with the lock recovered up to CARM_OFFSET_STEP_3_OF_3 state (#69704), the work stopped at 18:30UTC, we left the cavities locked on the infrared.

DAQ
Another event of data loss form suspensions happened at around 17:30UTC I recovered the data with at stop and restart of SUSP_Fb process.

The lock has been recovered up to step 3/3

the gains have been changed accordingly to the change of power (the ones that are not normalized)

the demodulation phases have been tuned (apart from Diff +)

Today afternoon, around 13h UTC we started the procedure to decrease the power towards the ITF. The power was lowered from 18W on the IMC transmission to 12 W. We followed the steps described below:

• We measured the TF of the IMC. The UGF was 110 kHz and the phase margin was 23 degrees;
• We moved the IPC1 and IPC8 rotators to adjust the power of the tranmission and reflection of IMC, respectively. The overall steps are summarized below:
  • cm_send('EIBAgilisRot','MOVEREL', 1, 1, 10600, 50) #IPC1
  • cm_send('EIBAgilisRot','MOVEREL', 4, 1, 3500, 50) #IPC8
• We changed the thresholds of some INJ signals:
  • RFC threshold: from 2.2 mW to 1.5 mW (MCMir DSP card);
  • IMC threshold: from 18 W to 12 W (IBMar DSP card) and also changed the variables 'LOCK' and 'IMC_trigger' on the VPM ISYS_Acl (lines 231 and 235);
  • FmodErr Z_Calib: from -5e-9 to -1e-8 (on metatron)
• Then, we engaged all loops and everything locked again. 
• Finally, we remeasured the TF of the IMC (see Fig. 1). The UGF is now 93 kHz and 26 degrees of phase margin.
• Fig. 2 shows the FFT of the main INJ signals and no significant difference can be seen.

To be noted that we didn't change the B2 signal, which now is 8.5 mW instead of 12.2 mW.

ITF found in locked arms.

At around 7:00 with Piernicola we went to NE to reactivated the green laser then the commissioning team recovered the DRMI state, see 69700.

Once recovered the ISYS team started working to reduce the input power.

ISC

Etalon setpoints changed and loops enabled:

2026-09-07 09h02m42 UTC    berni 'WI:WI Set point [WI_RH_SET=19.15,rampTime=1]' sent to LSC_Etalon_Acl
2026-09-07 09h02m45 UTC    berni 'WI:Enable servo' sent to LSC_Etalon_Acl
2026-09-07 09h02m52 UTC    berni 'NI:NI Set point [NI_RH_SET=19.53,rampTime=1]' sent to LSC_Etalon_Acl
2026-09-07 09h02m53 UTC    berni 'NI:Enable servo' sent to LSC_Etalon_Acl

TCS

In the first part of the shift Cecilia worked at  TCS TCS AuxCooling System, see entry 69697.

DAQ

At around 1:20 UTC we had a general loss of data: the data from Suspensions and TCS did not recover. At 13:44 UTC I contacted the DAQ on call; investigation in progress.

This afternoon we have updated the following thresholds on the detection system, in accordance with the reduction of the input power from 18 to 12 W:

• we updated the thresholds on SDB2_Photodiodes triggering the fast shutter for B1p_PD1, B1p_PD2 and B1s. All thresholds multiplied by a factor 2/3 in the configuration:

2026-09-07-13h18m00-UTC>INFO...-AcRelayChSet> B1p_PD1_DC_saturation - Trg01 0.55(3)- Trg10 0.39(1.5)
2026-09-07-13h18m00-UTC>INFO...-AcRelayChSet> B1p_PD2_DC_saturation - Trg01 0.78(1.17)- Trg10 0.19(0.29)
2026-09-07-13h18m00-UTC>INFO...-AcRelayChSet> B1s_PD1_DC_saturation - Trg01 30(45)- Trg10 15(22)

• Thresholds in ITF_LOCK.ini for B1p_PD1 have been reduced accordingly at 13h22 utc:
  • in the section SHUTTER: b1p_pd1_thr_lo = 0.3 > 0.2 ; b1p_pd1_thr_hi = 0.5 > 0.33 ; b1p_dc_thr = 0.04 > 0.027
  • in the section ITF_LOCK: b1p_pd1_thr_lo = 1.5 > 1.0 ; b1p_pd1_thr_hi = 3.0 > 2.0

• Thresholds in DET_MAIN.ini have also been reduced by the same factor at 13h24 utc, namely:

max_power_B1p = 0.04 > 0.027, max_power_B1p_PD1 = 0.44 > 0.29, max_power_B1s = 48 > 32

Both DET_MAIN and ITF_LOCK were reloaded at 13h26 utc

We recovered the DRMI state to allow the INJ crew to proceed with the reduction of the injected power. 

We needed to change a few phases that were preventing the lock:

DRMI_1F:

• MICH_phi0: -1.95 -> -2.35 
• PR_TX_GAIN 0.75 -> 0.55

DRMI 3F:

• MICH_phi0: -0.45 -> 3.7

Noticeably, the image of B1p is different from before, as it now looks like there are two beams impinging on the photodiode (Fig.1).