This afternoon also the TCS WI AUX laser has been turned on again, and left as the other ones ON for monitoring and thermalization.
The CO2 laser status is as follows:
All laser beams are blocked inside the benches.
Do not open the acoustic enclosures.
If access is required, please contact Marco and Ilaria.
Another quick look to the acoustic noise peak around 490Hz:
this one is not associated to the INJ HVAC, but switching it off (tests of July 28) caused the frequency of the peak to drift up: see Figure 1
the LB and EIB benches detect a correlated vibration, which is louder in the EIB (vertical accelerometer) than in the LB (horizontal acc.): Figure 2
Browsing back the VIM, the peak seems present since long time, but recently it has changed frequency and became more intense:
Hints may suggest for something located inside the INJ lab, probably on EIB, which is getting more noisy... maybe because of ageing?
ITF found in LOCKED_ARMS_IR in COMMISSIONING mode.
planned activities communicated to the ctrl room and performed:
- Camera installation on MC building (Fabozzi, external company) concluded at 10:20 UTC.
- OMC lock in NI single bounce (Gouaty, Romero) concluded at 10:00 UTC.
- DRMI recovery (w/o TCS) concluded.
- TCS - CO2 WI laser recovery (Nardecchia, Cavalieri, Gherardini) concluded at 10:00 UTC. TCS in standard state!
- CARM/DARM noise injections while on ALS (Bersanetti, Pinto) concluded at 13:30 UTC.
The activity on OMC lock in NI single bounce started at 07:12 UTC. Gouaty asked me to set ITF in SINGLE_BOUNCE_NI and misalign PR about 20 urad ty-. PR realigned upon concluded the activity.
ITF left in LOCKED_ARMS_IR.
We profited of some machine time to make noise injections on CARM and DARM, to be used to develop new control filters after the free space implementation.
Timestamps:
This morning, Fabio and Roberto performed additional checks on the electronics of the WI main CO2 laser. They found that the laser sync was intermittent: touching the sync board caused the signal to fluctuate. The board was therefore replaced with the spare one.
After the replacement, the WI main CO2 laser was switched on again at 09:49 UTC. The restart was successful: the laser reached its nominal output power and has remained stable since then (at least up to the time of writing), as shown in Fig. 1.
In the afternoon, Nicola reopened the cooling valve of the WI auxiliary laser, which was then switched on at 12:15 UTC.
The TCS is now back in its standard operating configuration: all CO2 lasers are on with all beams blocked on their respective benches.
Finally, together with Nicola and Diego, we updated the DMS. If any flip mirror on either CO2 bench is opened, allowing a laser beam to propagate toward the interferometer, the corresponding DMS status flag automatically turns red.
The CO2 laser status is as follows:
All laser beams are blocked inside the benches.
Do not open the acoustic enclosures.
If access is required, please contact Marco and me.
This afternoon also the TCS WI AUX laser has been turned on again, and left as the other ones ON for monitoring and thermalization.
The CO2 laser status is as follows:
All laser beams are blocked inside the benches.
Do not open the acoustic enclosures.
If access is required, please contact Marco and Ilaria.
This morning we performed some preparatory actions before the intervention on SDB1/SDB2 scheduled in 2 weeks. One of the goal was to test the DET python scripts (used for OMC lock and picomotor actuation on SDB1) to make sure they were still operational. We also took this opportunity to take an alignment reference in NI single bounce with the OMC locked, we adjusted the demodulation phase of the B1_PD3 photodiode, and we optimized the OMC alignment with 0 offsets on B5_QD2.
07h15 utc : Thanks to Nicola, the NI single bounce is set. SDB1 bench is in drift control.
At 07h07m10 utc, we open the OMC shutter.
Noticing that the correction in TX applied to the marionetta was around -5V, we acted on the motorized weight of SDB1 (BENCH_TX) by -25000 steps, to lower the correction up to 0.4 V.
At 7h48m25 utc we remove the offsets of the B5_QD2 quadrants (the ones used for ITF lock). This gives us an alignment reference for the single bounce (with B5 QD2 offsets at 0), while B1p is well centered on the camera (within +/-50 um from the center).
We observe that the initial OMC temperature was 22.55 deg.
Between 7h50 and 8h40 we tried several time to lock the OMC but we faced the following problems:
OMC was locked at 08h42m50 utc (See attached figure). Power on B1_PD3 is initially equal to 12 uW.
We adjusted the OMC alignment by acting on the picomotors, and reached a power on B1_PD3 equal to ~15.7 uW.
At 9h11 utc we start an OMC scan to check the quality of the alignment.
Order 1 = 0.4 uW > This gives an alignment defect of 2.5%
Order 2 = 0.3 uW > This gives a mode mismatch of ~2%
We restored the dark fringe offset for B5_QD2, closed the OMC shutter and concluded our activity.
After commissioning the west-arm instrumented baffle, we locked the cavities, kept the input mirrors centred, and performed a very slow-moving snail scan simultaneously with both end mirrors for more than half an hour, starting at approximately 12:45 CEST, Aug 6th.
The objective was to collect data from all the baffle sensors for the relevant studies of the baffle’s performance. The snail scan was perfect for this purpose, as it allowed the laser beam to pass successfully over all the sensors.
In order to evaluate the eventual improvement of the angular control due to the intervention on sensing and driving, one can compare data regarding the lock of the arms before and after the activity. The first data collected in the evening were clearly affected by a new kind of instability, characterized by short spikes. Apparently the reason was a drift of PR from the correct parking position, pruducing resonaces of the arms with a sporious reflected beam. A few hours later an additional misalignment has been applied to PR and the effect has been removed, as shown by the trend of B7_DC_max and B8_DC_max.
In order to evaluate the eventual improvement of the angular control due to the intervention on sensing and driving, one can compare data regarding the lock of the arms before and after the activity. The first data collected in the evening were clearly affected by a new kind of instability, characterized by short spikes. Apparently the reason was a drift of PR from the correct parking position, pruducing resonaces of the arms with a sporious reflected beam. A few hours later an additional misalignment has been applied to PR and the effect has been removed, as shown by the trend of B7_DC_max and B8_DC_max.
The new system is now working steadily, at around 1.8 (NI) - 2 (WI) liters per minute.
Before shutting the old system off, issues and anomalies with the flows (both NI and WI) were observed.
This phenomenon can be a consequence of the following issues:
Clogging in the piping
Clogging in the fittings
Clogging in the utilities
Old or damaged flowmeters
Presence of air
Insufficient circulators
Losses in the circuit
The new cooling system was designed specifically to comply to the correct water treatment and choice of materials to avoid future corrosion, deposition, erosion, pitting or biologic contamination and the flowmeters already in place were replaced. Air was completely removed and the circulator's power was doubled (from a single one for two branches to two separate ones).
Still, the measured flow of the new system was the same or lower than the old one, even when switching back to the old flowmeters, that show the same measurements as the new ones.
First thing that needs to be taken into account is that during the installation the system remained filled with still water for more than a month, so if any debris were present they might have deposited.
This is why Nicola, Piernicola and I carried out a thorough cleaning of every piece of piping and every fitting, laser area included, with air, mechanical friction, alcaline soap and both alcohol and ultrapure water ultrasound bath.
We inverted the laser's inlet and outlet from the circulators onwards and closed the system on itself at every level. The results are the following:
The flow up to the split among the utilities, under the bench, is 10 l/min.
After the splitting into 8 utilities, it decreases to 2 l/min (acceptable according to the laser manufacturer)
We tested every utility and found some beam dump to be completely clogged so that not even air could go through. The laser, nevertheless, after being cleaned with dust-free cloths and distilled watere, showed no working issues.
While dismantling and cleaning the old system, debris were collected and biological contamination was observed. They will be sent to an external laboratory to be analized.
Water pH was between 6 and 6.5.
TDS document addressing pollution in cooling systems coming soon
From a quick look:
The excess noise above 2kHz engaged as well on May 7th: as shown by VIM in Figure 1
This noise seems associated to the INJ HVAC: as it went off and on at the time of its switching off/on on July 28th : Figure 2.
This morning, according to the planned schedule, we attempted to switch on the NI and WI main CO₂ lasers.
After Nicola and Cecilia successfully restored the chillers and the Guardian system, the NI and WI main lasers were switched on at 08:17 UTC and 08:18 UTC, respectively.
Unfortunately, after about 1 minute and 40 seconds of operation, the WI main laser unexpectedly switched off (fig.1). Several attempts were then made to restart it, but without success.
At that point, Roberto and Flavio joined the investigation, and a series of checks was performed to determine whether the problem was related to the laser itself or to the driving electronics.
A visual inspection of the bench, including the BNC connections and the laser itself, did not reveal any obvious anomaly. The laser status LED was correctly lit in red, and all RF driver dongles were green, as expected.
After closing the bench, we performed one final startup attempt. This time the WI laser switched on, but only at approximately half of its nominal power. After another power cycle, the laser briefly reached its nominal output power before dropping again to approximately half power (fig.2).
During the brief period in which the laser reached nominal power, I acquired a thermal camera image of the DAS beam (fig.3). No anomalies were observed.
These observations suggest that the problem is more likely related to the electronics than to the laser itself. To be understood.For safety reasons, we decided to switch off both lasers on the WI bench.
At the time of writing, the laser status is as follows:
The WI main chiller is off. The backup chiller is connected only to the NI.
For the auxiliary chiller, the valve to the WI branch has been closed to avoid circulating cold water through the switched-off WI laser.
================================
As a side note (but an important one), I am experiencing significant difficulties with online monitoring using Data Display, even when using the previous version (Dy/v11r2/Linux-x86_64-AL9). While monitoring the channels, the displayed data frequently disappear for several seconds before reappearing. After some time, the application freezes completely and has to be restarted (see Fig. 4 for an example).
This morning, Fabio and Roberto performed additional checks on the electronics of the WI main CO2 laser. They found that the laser sync was intermittent: touching the sync board caused the signal to fluctuate. The board was therefore replaced with the spare one.
After the replacement, the WI main CO2 laser was switched on again at 09:49 UTC. The restart was successful: the laser reached its nominal output power and has remained stable since then (at least up to the time of writing), as shown in Fig. 1.
In the afternoon, Nicola reopened the cooling valve of the WI auxiliary laser, which was then switched on at 12:15 UTC.
The TCS is now back in its standard operating configuration: all CO2 lasers are on with all beams blocked on their respective benches.
Finally, together with Nicola and Diego, we updated the DMS. If any flip mirror on either CO2 bench is opened, allowing a laser beam to propagate toward the interferometer, the corresponding DMS status flag automatically turns red.
Acoustic noise inside the INJ room has changed significantly between the most recent switch off (July 28, https://logbook.virgo-gw.eu/virgo/?r=69458) and the previous which was in November (Nov. 27 2025: https://logbook.virgo-gw.eu/virgo/?r=68269). The changes are shown in the LAST plot attached comparing mics ASD. We tried to track these changes and found the following:
Reduced 20Hz acoustic bump:
On June 18th the RETURN fan frequency of INJ HVAC was changed from the usual 21 Hz to 14 Hz, and the acoustic bump around 20 Hz reduced significantly: Figure 1 and Figure 2. This is consistent with (but more pronounced then) what observed in our quick slow down in https://logbook.virgo-gw.eu/virgo/?r=67829 (return fan moved only down to 17Hz). We do not know why this reduction to 14 Hz was done, but the HVAC is running in this way since then. Good news is also that the environmental parameters seems not significantly affected (Figure 3).
Acoustic bumps 40-120 Hz changing level:
Examing VIM spectrogram back since Dec 2025, we noticed that in a number of occasions (see Table) some acoustic bumps in the INJ room mics increased or reduced. Bumps are roughly at 40, 60, 80 120 Hz. Figures 4 to 8 show some of these occurrences. The last increase happened on May 7th, and the noise condition is this since then. It looks that these occurences coincide with people entering and then leaving the INJ area (seismic activity). Examining some occurences, we often find a change in the pressure of the INJ room, yet no change in the fans' frequency: see in Figure 9 and following.
Excess noise around 490 Hz and above 2kHz: this has to be investigated .... :-)
A list of these occurences:
| UTC | |
|---|---|
| Dec. 13 around 12:00 | increase |
| Dec 15 around 8:00 | further increase |
| Dec 30 around 10:00 | decrease |
| Feb 2 around 9:00 | increase |
| Fec 14 around 7:00 | decrease |
| March 5 between 10:00 and 12:00 | increase |
| March 10 around 10:00 | increase |
| March 24 around 9:00 | decrease |
| May 4 around 7:00 | increase |
| May 7 starting from 14:00 (after long access) | further increase |
From a quick look:
The excess noise above 2kHz engaged as well on May 7th: as shown by VIM in Figure 1
This noise seems associated to the INJ HVAC: as it went off and on at the time of its switching off/on on July 28th : Figure 2.
Another quick look to the acoustic noise peak around 490Hz:
this one is not associated to the INJ HVAC, but switching it off (tests of July 28) caused the frequency of the peak to drift up: see Figure 1
the LB and EIB benches detect a correlated vibration, which is louder in the EIB (vertical accelerometer) than in the LB (horizontal acc.): Figure 2
Browsing back the VIM, the peak seems present since long time, but recently it has changed frequency and became more intense:
Hints may suggest for something located inside the INJ lab, probably on EIB, which is getting more noisy... maybe because of ageing?
ITF in COMMISSIONING, DOWN
Activities reported to the control room:
The assembly of the new cooling system for the TCS auxiliary lasers is complete.
It is a two-stage system (pic 1 - schematics)
1. Primary stage –. The tank temperature is maintained by one of two chillers, operating in a redundant configuration: one unit designated as the primary chiller (working) and a second unit
as a (non operating until needed) backup, to ensure continuous operation. In case of failure, the operator on shift will only have to switch the piping from one chiller to the other (pic 2: AuxCooling Chiller)
2. Secondary stage – From the tank (pic 3 - AuxCooling Tank), water is distributed through two separate piping and valve systems, one per laser (pic 4 (temporary) - Distribution and post-heating system assembly phase). Each system includes four pipe collar heaters, enabling post-heating control of the oscilations in temperature, to keep them within the 0.1 limit (more details in future entries that will be posted as comments of this one).
New sensors were installed and new channels were created, soon to be implemented on DMS. Together with the old ones, the system can be monitored using (see schematics):
The new system is now working steadily, at around 1.8 (NI) - 2 (WI) liters per minute.
Before shutting the old system off, issues and anomalies with the flows (both NI and WI) were observed.
This phenomenon can be a consequence of the following issues:
Clogging in the piping
Clogging in the fittings
Clogging in the utilities
Old or damaged flowmeters
Presence of air
Insufficient circulators
Losses in the circuit
The new cooling system was designed specifically to comply to the correct water treatment and choice of materials to avoid future corrosion, deposition, erosion, pitting or biologic contamination and the flowmeters already in place were replaced. Air was completely removed and the circulator's power was doubled (from a single one for two branches to two separate ones).
Still, the measured flow of the new system was the same or lower than the old one, even when switching back to the old flowmeters, that show the same measurements as the new ones.
First thing that needs to be taken into account is that during the installation the system remained filled with still water for more than a month, so if any debris were present they might have deposited.
This is why Nicola, Piernicola and I carried out a thorough cleaning of every piece of piping and every fitting, laser area included, with air, mechanical friction, alcaline soap and both alcohol and ultrapure water ultrasound bath.
We inverted the laser's inlet and outlet from the circulators onwards and closed the system on itself at every level. The results are the following:
The flow up to the split among the utilities, under the bench, is 10 l/min.
After the splitting into 8 utilities, it decreases to 2 l/min (acceptable according to the laser manufacturer)
We tested every utility and found some beam dump to be completely clogged so that not even air could go through. The laser, nevertheless, after being cleaned with dust-free cloths and distilled watere, showed no working issues.
While dismantling and cleaning the old system, debris were collected and biological contamination was observed. They will be sent to an external laboratory to be analized.
Water pH was between 6 and 6.5.
TDS document addressing pollution in cooling systems coming soon
We commissioned the WI instrumented baffle for the prealignment of the WE, repeating the procedure used yesterday for the NI (69514)
The starting position for the WE is (TX; TY) = (24.5; 136.8) urad
We then swept the NE right by about 100 - 110 urad until we intersected the symmetrical column c5 and repeated the process. Overall, the power detected were:
The median point identified by these positions is (<TX>;<TY>) = (24.5; 136.9) urad.
We repeated the process with a vertical scan:
The median point identified by these positions is (<TX>;<TY>) = (25.3; 136.5) urad.
We were able to apply the procedure much faster, as we become more familiar with the behaviour of the baffle, and the obtained accuracy is still within a few urads from the well aligned position of the WE.
This afternoon, both CH CO₂ lasers were successfully switched on using the new cooling system designed and installed by the EGO team.
Before switching on the lasers, Piernicola performed a complete check of both CO₂ benches. In particular, he reset the zero level of all power meters and verified the correct operation of all remotely controlled flip mirrors.
The lasers were then switched on sequentially:
For both lasers, the pulse width was set to 160 µs. For reference, the maximum output power is achieved with a pulse width of 199 µs.
The laser behaviours observed so far are shown in Fig. 1.
The lasers will remain ON overnight. According to the current plan, the main CO₂ lasers will be switched on tomorrow morning.
I also performed a quick check using the thermal cameras on both benches and acquired one thermal image of each CH beam. A comparison with the images acquired on 2026-04-07 did not reveal any significant changes in the beam propagation. The comparison is shown in Fig. 2.
Side note: while trying to copy the thermal camera images from PCINFRACAM to the control machines, I noticed that the procedure was no longer working. I therefore contacted the Computing Team, and Elian found that the old SSH Secure Shell client is no longer supported following the recent Linux upgrade. As a temporary workaround, Elian identified an alternative procedure and shared it with all operators to be used during the upcoming Tuesday maintenance.
ITF found in COMMISSIONING Mode and LOCKED_ARMS_IR State.
All times are UTC.
06:38 - 06:49 Recovered SBE_SPRB vertical position with loop closed (operator).
07:10 - 10:30 Instrumented baffle commissioning (Vallejo, Boldrini. #69514).
07:41 - 11:00 Activity on TCS AUX Cooling System (Dattilo, Cavalieri).
11:39 - 12:35 Safety inspection at MCB and WEB (Fabozzi, external personnel).
12:07 - 15:07 Activity on TCS AUX Cooling System (Dattilo, Menzione, Cavalieri).
13:20 - 14:00 TCS CH Lasers ON and Flip Mirrors checked (Spinicelli, Nardecchia from remote).
13:20 WE PCal laser turned ON (Rolland from remote, #69513).
13:31 - ONGOING Suspensions tuning (Ruggi, Pinto).
ITF left in DOWN State and in COMMISSIONING Mode.
We attempted to evaluate how the instrumented baffle could be used to prealign the end mirrors of the arm cavities.
Starting from the locked arms, we took references of the alignment condition of the test masses, of the BS and of the transversal position of the PR (Figs.1,2), we then unlocked the interferometer and misaligned both ITMs by 60 urad on TY to simulate the stage of the recovery when the beam has been centered on the ETMs using the markers by moving the PR and the BS, but the alignment of the test masses themselves is still unknown.
The starting position for the NE is (TX; TY) = (-107.8; 45.4) urad
Once we did that, we started sweeping the NE alignment until the sensors on the NI instrumented baffle detected power. We then refined the alignment of the NE until we maximized the power detected by sensors 0,1 and 2 of the column c17, in the left sector of the baffle. The goal was to use the detected power to attempt to center the beam on the middle sensor, equalizing the power on sensors 0 and 2, assuming that they correspond to the tails of the Gaussian profile of the beam. We achieved this result on the c17 column with intervals of 0.2 - 0.4 urad for the NE, notice that the procedure is cumbersome, because the detected power fluctuates significantly so one needs to be patient and consider an average over a minute or so.
We then swept the NE right by about 100 - 110 urad until we intersected the symmetrical column c5 and repeated the process. Overall, the power detected were:
The median point identified by these positions is (<TX>;<TY>) = (-105.53; 44.56) urad, that is remarkably close to the initial position.
We repeated the process with a vertical scan:
The median point identified by these positions is (<TX>;<TY>) = (-105.68; 43.96) urad, which is also close to the initial alignment of the NE.
Our conclusion is that the instrumented baffle is accurate enough to provide a prealignment of the beam that centers it on the NI withing a few urads from the correct alignment, so it seems a promising tool to be used in future recoveries.
We tried to repeat the process for the WI instrumented baffle, but we could not finish the procedure in the remaining time of our shift. Another commissioning windows has been allocated for this tomorrow morning.
WE PCal switch on at 13h20 UTC.
Yesterday afternoon, we performed a measurement of the current input beam mode mismatch toward the arms, with the CO2 lasers off (only PR Chrocc and SR RH are at nominal value).
Since the interferometer is not actually fully locked, we decided to use the green beam scan of the arms to assess the cold mistmach.
The scan started at 14.05UTC of the August 4th.
The results are shown in fig. 1, with both arms around ~1.5% of mistmatch.
N_matching = 1.6e-02
W_matching = 1.3e-02
The following report summarizes the measurement and analysis of scans performed on 03-08-2026 in order to measure the arm Gouy phase. The aim is to verify that we recover the same Gouy phase as it was during the end of the last observation run. The Gouy phase is measured from the mode spacing measured from the frequency scans. The procedure to perform the slow FSR scan can be found on this page https://wiki.virgo-gw.eu/Commissioning/OptChar/Opt_Char_shift
Measurements:
At 14:54 UTC, ITF is locked using the state LOCKED_ARMS_BEATING
At 14:55 UTC, 1 iteration of scan is run as a test to verify that everything work
At 15:00 UTC, 15 iterations of scan, ended at 15:33 UTC
Results:
Tables 1 and 2 compare the mode spacing of the first four higher-order modes during the end O4 run and in the scan measured on 2026-08-03 in the west and north cavity, respectively.
Table 1 : North Cavity
| HOM 1 | HOM 2 | HOM 3 | HOM 4 | |
| 02 December 2025 | 0.1035±0.0003 | 0.2092±0.0003 | 0.3191±0.0002 | 0.4276±0.0002 |
| 03 August 2026 | 0.1057±0.0003 | 0.2113±0.0002 | 0.3215±0.0002 | 0.429±0.002 |
The measured mode spacing is very similar in each scan but slightly larger in the recent scans.
Table 2 : West Cavity
| HOM 1 | HOM 2 | HOM 3 | HOM 4 | |
| 02 December 2025 | 0.10246±0.0007 | 0.2076±0.0002 | 0.3201±0.0002 | 0.4304±0.0005 |
| 03 August 2026 | 0.103±0.001 | 0.2085±0.0008 | 0.3195±0.0003 | 0.4290±0.0003 |
The measured mode spacing is very similar in each scan, larger in the recent scan for the first two higher-order modes and smaller for HOM 3 and HOM 4. A supposition to explain the discrepancy between the different higher-order modes could be the change of the input test masses, resulting in a different transverse RoC asymmetry. The higher-order modes, presenting a larger area, experience a different portion of the mirror surface and as a result experience a different effective RoC. This hypothesis could explain why for HOM 1 and HOM 2 the mode spacing is larger during the scan performed on 03 August 2026 and smaller for HOM 3 and HOM 4.
To visualize what the observed difference represents in the scan, Figure 1 and Figure 2 show two scans plotted together. The blue curve represents the median scan performed on 03 August 2026 and the orange curve the old scan performed on 02 December 2025. The four plots below the full scan are a zoom on the first four higher order modes. These plots show that the difference is actually very small, suggesting that the Gouy phase is almost the same as in December.
ITF found in DOWN with the automation requesting to lock in BEATING_DRMI_1F.
The DRMI_LOCK node was also stuck trying to reach the requested state MISALIGNED_PR_SR; to unblock the situation I restarted the nodes.
After that I performed a manual prealignment of WI mirror and I relocked the cavity.
At 6:00 UTC started the planned maintenance, below the list of the activity communicated in control room:
All the maintenance activities concluded around 10:30 UTC.
In the afternoon the INJ team worked input beam mode matching measurement, activity in progress.
Other
M 4.3 in Pisa; the earthquake opened the PR ID loop and all the SBE loops. Properly closed.
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