Looking at recent data when the INJ air conditioning was off (https://logbook.virgo-gw.eu/virgo/?r=68269) we noticed that the microphone on the laser bench measures some, not large but significant, excess acoustic noise with respect to the microphone in the room (_LLR_) and the microphone on EIB.
This noise shows up mostly between about 200Hz and 2 kHz. Most evident peaks are around 370Hz and 635Hz, which are very coherent with LB vibrations. There seems to be an excess noise also around 30-80Hz, but this is less coherent with the LB accelerometer.
It seems to us an indication for some acoustic-vibration source positioned on the LB. Since the HVAC is off, the source is unlikely related to air turbulence underneath the LB cover. One suspect might be the chiller water flow. To be investigated.
When the HVAC is on -- second figure -- this noise is less visible because partially covered, but two coherent bumps aroud 370Hz and 635Hz are still evident.
To be noted other two bumps present in all microphones, most evident when HVAC is off. They are at about 12 Hz and 18.5 Hz. These might be acoustic modes of the room.
4/02 Realignment of the squeezer
In the Morning we tried to align the PD photodiodes but we lost a bit the CMRR of the HD, and we also tuned a bit the EQB1 FI HWP1
Martina went in Det lab to exchange the discs for the dust monitoring so she also realigned the MZ and the OPA. We did not gain much in terms of MZ visibility Max ~1.6V. But we improved a bit the level of the coupling of the green beam into the OPA cavity.
5/02 Fine tuning of the alignment
As last work on the DL we aligned better its mirror, recovered the HD PD alignment and tuned again the HWP of EQB1 FI and the one in front of the HD Detector
We also restored the lock of all the PLLs
We investigated a bit a possible effect of phase noise
For all these operation we did a CC phase scan here a summary table
| Time | Param Gain | Efficiency | Phase Noise | SQZ Level | ASQZ Level | Notes | Fig |
| 02/02 18:47:44 | 0.3826 = 8.34 dB | 94.8(2)% | 92(2) mrad | 6.12 dB | 8.11 dB | Laser Multimode (Stand Alone) - After DL alignment | Fig 1 |
| 03/02 14:35:42 | 0.3788 = 8.4307 dB | 92.8(2)% | 77(2) mrad | 6.15 dB | 8.13 dB | Main PLL offset moved (no more multimode) | Fig 2 |
| 04/02 09:56:12 | 0.3601 = 8.87 dB | 91.9(2)% | 65(2) mrad | 6.40 dB | 8.54 dB | DL alignmen - t Stand alone - No multimode | Fig 3 |
| 04/02 18:04:36 | 0.3474 = 9.18 dB | 88.4(2)% | 20(2) mrad | 6.47 dB | 8.71 dB | Lost a bit HD alignment, OPA alignment No multimode | Fig 4 |
| 05/02 10:27:27 | 0.3523 = 9.06 dB | 92.1(2)% | 66(2) mrad | 6.48 dB | 8.73 dB | Improved HD alignment | Fig 5 |
| 05/02 13:56:06 | 0.3587 = 8.9 dB | 94.3(2) % | 85(1) mrad | 6.38 dB | 8.65 dB | No alignment, PSL laser freq Shift all PLL locked | Fig 6 |
| 05/02 15:48:44 | 0.402 = 7.91 dB | 94.1(2) % | 110(1) mrad | 5.53 dB | 7.34 dB | Less generated squeezing/ no alignment | Fig 7 |
Phase scans in similar configurations gives a different level of losses and phase noise. In general the losses are under control between 6 and 10 % whereas it seems we have an excess of phase noise. To be investigated.
The amount of losses is quite well explained (4% from visibility) 1% OPA escape efficiency 1% HD PD Quantum efficiency 1% EQB1 FI 1%HD clearence. Known losses 8%
If we do an average of the results above the level of losses is 7.4±0.8% and the phase noise is 74±11 mrad. In September 2022 (with the Pump power scan) we obtained 11.0 ± 0.4% of losses, 14±12 mrad of phase noise.
Next step is to remove the delay line
We removed the DL and we started to reflect sqz with SQB1 retroreflector. To optimize we did the following steps
- remove DL
- Close CC (Fast and corse loop)
- Close HD AA in ASQZ
- Move Retroreflector X and Y to remove clipping
- Move EQB1 HWP2 (HD) until we maximize the mag in SQZ
- Move SQB1 HWP2 (FI2) until we maximized the mag
- Move SQB1 (HWP1) (FI1) by reducing stray light bump on HD DIff
We performed a phase scan that should be analuzed at GPS: 145354929
Note that before aligning the retroreflector we tried to aligne the PD for SC into OPA AA but without managing. We centered as better es possible the PD by looking its aperture. Further investigations will be done
Here the new set point of Squeezing PLL
PLL MAIN: 29668
PLL CC: 29640
PLL SC: 36026
ITF found with the two cavities locked.
The SR tower evacuation is in progress, nothing to report on this side.
Other activities carried out during the day:
- Crystal temperature change of the ML;
- in the morning the HVAC team worked on the WE ACS system;
- Squeezing recovery, still in progress;
- at around 14:30 UTC Diana (TCS) started an activity in CB, still in progress.
After the change of the crystal temperature of the last summer, the main laser of the squeezer was too far from the Virgo ML (see here and there).
In agreement with Marco, we lowered the Virgo ML temperature by ~0.45⁰ to try improving squeezing system stability, which seemed to be stable in July. PSL/INJ system relocked quickly after the operation (a check of the OLTF of the IMC didn't spot any problem).
The locking of the squeezer laser is ongoing.
We will check in the following days the stability of the PSL/INJ to be sure the new T setpoint is stable enough.
Here the new set point of Squeezing PLL
PLL MAIN: 29668
PLL CC: 29640
PLL SC: 36026
Through analysis from geophones and LVDTs signals around SWEB, SNEB, SIB2, and SDB2, resonance frequencies lower than expected were identified.
In the case of SWEB, a first resonance mode was theoretically calculated at about 45,8 Hz. However, modes around 22 Hz and 26 Hz were identified by plotting transfert function between geophones and suspension ‘s LVDTs.
The reason for this discrepancy between theoretical calculations and experimental results is therefore questioned. The objective is, through an experimental vibration test using an impact hammer, to identify the resonance modes and understand their origin.
Test Principle:
The experimental vibration test using an impact hammer is a method used to characterize the dynamic behavior of a structure. It consists of exciting the structure using an instrumented hammer equipped with a force sensor. The vibratory response of the structure is measured using accelerometers placed on the structure under investigation.
The combined analysis of the impact force signal and the measured responses permit to determine the Frequency Response Functions (FRFs), from which modal parameters such as natural resonance frequencies, mode shapes, and damping coefficients are identified.
To increase the number of measurement points, it is possible to:
• always strike the same location and move the accelerometers
• fix the accelerometers in place and move the impact point (option chosen)
Experiment:
We have one impact hammer and three accelerometers available.
Installation of the equipment began on Monday, 02/02, at around 2:30 p.m.
The accelerometers were positioned respectively at the centre of each door and at the top of the dome.
A first series of tests was carried out in the afternoon to validate the setup and verify the consistency of the measurements.
Although this was not sufficient to obtain a good representation of the modal shapes, it was already possible to observe resonances around 22 Hz and 26 Hz, and then at 45 Hz.
The following day, Tuesday 03/02, we refined the model using parameters allowing better resolution at low frequency. Experimental set up had been configured to measure transfer function between accelerometers and instrumented hammer in 0 to 100 Hz range. (see attached parameters)
From 2:00 p.m., we started a new measurement campaign consisting of 110 impact points distributed as evenly as possible around the minitower. As some areas were inaccessible, certain desired impact points had to be removed or relocated.
The frequency response was estimated from the average of three impacts (at the same point and in the same direction).
This measurement campaign allowed us to confirm the resonance of SWEB at 22.6 Hz, 26 Hz, and then 45,2 Hz.
Thanks to the large number of impact points, we obtained a relatively good estimation of the modal shapes. (see attached charts)
At 22.6 Hz, the minitower appears to oscillate in an almost rigid-body manner along the x-axis.
At 26 Hz, the minitower oscillates this time along the z-axis (y-axis on our model).
At first glance, these look like pendulum modes (almost rigid-body OR hinge movement around fixation plates). Without y-axis measurement, it is not possible to define more precisely.
Observations and perspectives:
Clearances were observed between the feet of the minitower and the shims/ground. At the location of some bolts, this clearance reaches up to 1.8 mm.
This could support the hypothesis of inadequate anchoring to the ground.
However, on SDB2, clearances between the feet and the ground are also observed, while the resonance frequency remains higher (around 31 Hz). Two main differences between SWEB and SDB2 can be identified: the presence of vacuum pipes instead of two oblong flanges and the way the fixation plates are welded to the feet (discontinuous on one side compared to continuous on both sides). (see attached pictures)
To obtain a more precise understanding, adapting the numerical modal analysis is the first objective. If this is not sufficient, carrying out a new measurement campaign on SDB2 could be valuable. Finally, correctly tightening every SWEB screws before re-measuring the resonance frequencies appears to be enriching.
We noticed that in all the scans the shot noise level was not well normalized and was aeoind -0.1dB. So we changed the normalization factor from 276548 to 278820
This described the work done the 4th of February 2026 on SWEB mini-towers.
One of the 4 bolt of the North-west foot of SWEB was found loose, it is the one located in the east south corner of the foot.
A comparator has been set-up on the feet about 2 cm from the loose bolt to monitor the distance of the feet to the feet.
The arm was locked on the IR, and the position loop of SWEB was open keeping the angular loop closed.
First the bolt was tighten a bit in 3 steps so that the feet moves down by 0.1 mm.
The drift control of the bench was active, the readout of the position at the bench level changed like this :
X from 356 µm to 225 µm
Z from 312 µm to 390 µm.
We can interpret as a motion of the mini-tower in the direction to the arm (east) and to the south.
Then at 13:45 UTC, the bolt was loosened again, the LVDTs signals from the bench came back to the same position as before tightening it.
Then the bolt was tighten again so that we feet moves down by 0.2 mm (as can be seen by the comparator), concluded at 13:54 UTC.
SWEB_LC_X went to 95 µm and SWEB_LC_Z to 475 µm.
The arm kept locked all the time.
The bench position loop was then closed with the following set-point:
X = 95 µm
Y = 900 µm
Z = 475 µm
The angular loop with drift control, is now at :
TX = 5.75 µrad
TY = 1776.6 µrad
TZ = 23 µrad
Fabio check that the green beam can be locked on the arm but a more thorough look by ALS expert is needed.
Figure attached shows the Local Control Signal during the operation.
No clear conclusion so far on the effect of tightening this bolt.
02/02/2025 Improvement of delay line alignment
We started the work with the laser in the good state, High Magnitude ~8mV so we decided to profit witht he sistuation and work with the delay line alignment.
We acted mostly on DL_M4 in both the degree of freedom and we managed to improve the magnitude level and the antisqueezing level. At the end of the operation we also checked how much the squeezing was improved and we saw an improvement of ~0.3dB
We performed a Coherent control loop phase scan and we managed to measure ~8dB of anti squeezing and 6.3 dB of squeezing with 8.3 dB of generated squeezing. (Fig1). Phase noise 63mrad losses 8%
03/02/2025 CC Laser mode hopping
We started the activity in the bad state of the CC laser. So we decided to investigate about the cause of this issue. For us it is impossible to improve the alignment if the amplitude of the 4 MHz magnitude on the HD detector is fluctuating.
The first test was to change the gain of the CC PLL to see if it was a servo bump of the loop causing some issue. But we did not see any effect in the magnitude
As second step we tried to keep again the MAIN PLL unlocked and we chenged the temperature of the main Laser with the CC PLL locked. We increased the absolute number of the Temperature set. We started from 31568 as starting value for the slow output of the CC PLL and the CC PLL started to unlock fbetween 31720 and 31740, i.e. when the CC Laser temperature was changed by 40mK, i.e. its frequency by about 120 MHz. In this situation we did not manage to lock anymore the CC PLL. During this change of temperature we noticed that the HD 4MHz magnitude decreased every step. Possible explanation: we started with the laser in a multimode configuration and after 120MHz the energy was more in the other peak and the CC PLL was not able to lock anymore.
We wanted to explore the other direction to understand if the laser was more stable and to understan how much we need to move the CC PLL frequency and the MAIN Laser frequency. At that point Fiodor pointed out this entry https://logbook.virgo-gw.eu/virgo/?r=51719 in wich they experienced the same situation.
The idea is to add EQB1_HD_MIR i.e a mirror in front of the HD detector to redirect the beam going to PD2 toward a photodiode and two cameras out of the HD box. The name of the PD channel is EQB1_IR_PD_MONI. HD_MIR pos = 0 means that the Mirror is out from the way, and HD_MIR pos = +9000 steps means that the mirror is in the beam and the PD receive light. After that we remembered that the CC power is very low and it is impossible to see on the photodiode without removing the filter in front of it. So we removed the filter in front the external PD that is called "IR PD Filter" in the process EQB1_ThorAct.
We then scanned the OPA cavity, after OPA cavity in the direction of IR_PD_MONI, the Green beam is filtered and only the LO and CC beam are sent toward this PD. We thus shuttered LO and on the PD we saw only the CC. Looking the cavity scan (we saw multiple peaks) and moving the CC PLL by -1400 steps only one peak was visible (Fig2).
1400steps means 0.35V i.e. 0.35C in temperature of the laser.
We wanted to test the system in this point so we moved the temperature of all the laser. So the new working point is: PLL_MAIN = 30120 CC_PLL=30038 SC_PLL=37966. The starting point was: MAIN_PLL= 31544 CC_PLL=31423 SC_PLL = 38040.
In this point we bot checked the the stability with the system in anti-squeezing and we also di another phase scan of the CC. See fig 3 and 4. Phase noise 40mrad losses 10%
In this configutation the system is more stable but now squeezing can not be injected into the interferometer because the MAIN LASER of the squeezer is about 1.2GHz faar from Virgo Laser.
This problem started after this work in last july https://logbook.virgo-gw.eu/virgo/?r=67348 in wich the temperature of the ITF laser was moved by 1.4degree from 22.7 to 24.1C. In order to lock the MAIN PLL in this new working point the solution should be move the PSL Laser by ~0.35 degree i.e around 23.75 C.
03/02/2025 Check During night
We checked the behaviour during the night and we noticed that at the beginning was not aligned. After that was stable for a while and that some multimode behaviout occurred again. So probably 0.35 C is not enough and it is better to change by 0.45 i.e to 23.65 C if it is possible from INJ system
This morning I found the two cavities locked; the SR tower evacuation is going out smoothly; others activities carried out during the day:
- minitowers mechanical survey (SNEB, SWEB and SDB2), activity completed;
- recovery of the squeezing system, ongoing.
Air Conditioning
from 10:40UTC to 12:30UTC I set the detection area air conditioning system in "Portata Nominale" to allow the work on SDB2;
SBE
recovery of SWEB vertical correction with F0 step motors from 8:25UTC to 8:35UTC.
Today at 9:31 utc, the NNN axial position sensor presented a glitch (see top left plot of attached picture). It seems not to be related with a real NCal move since all other sensors from the same platform behave normally.
Due to this glitch (maybe due to a power supply proble ?), an automatic security action switch the enable boolean of the rotor to false (bottom right plot of the picture) and the NCal stopped, raising the DMS alarm.
Around 15:30 UTC, we restarted the NNN Ncal successfully and we will keep an eye on this.
The new baffle has an aperture whose diameter is 150 mm. The increase of 1.3 kg load was compensated by removing two stops of the marionette (in total 2.04 kg) and readjusting the weight.
The motors were checked. The motor labeled as Tz indeed moves but with anomalously slow speed, probably the grip on the screw is loose. Anyhow it moves in both directions. During the tests we were able to appreciate that 1 g on the tip of the magnet mount produces a significant number of steps (a few hundreds).
Some further work was needed because the beam of the mirror optical lever, slightly miscentred on the mirror, did not reach anymore the sensor after the reflection (Fig1). After the work on the optical lever the beam has similar clearance on the two sides. and allows full range dynamics on the sensor (Fig2).
The Optical lever of the mirror is not anymore the pre-aligned reference so far.
The system was left in the hands of VAC team to finalize the evacuation in the late afternoon.
14:00 UTC beginning of the shift, ITF in DOWN UPGRADING
14:30 UTC SR tower closed, vacuum pumping started, cryovalves opened
19:30 UTC SWEB position loop closed
18:00 UTC recovery of the arms: I moved NE, NI, WE, WI, BS, PR TY/TX back to their last locked position and so did I with PR F7_Y. Arms wouldn't relock, I managed to lock the west arm by misaligning both WE and WI by a couple urads. After moving the PR vertically, I finally locked the north arm misaligning NI TX by 15 urads.
21:25 UTC recovery of the arms completed, arms locked, PR in the same angular and vertical position of the last lock on Thu 30th Jan. Automation left as found with ITF_LOCK and DET_MAIN in pause.
22:00 UTC at the end of the shift the ITF was left in DOWN UPGRADING with ARMS LOCKED
Subsystem reports
CALI
NCal rotor permutation and power supply repairs (#68617 Van Hove, Mours)
SBE
SWEB measurements activity carried out throughout the day until about 17:00 UTC (Deleglise)
PAY
SR baffle installed, payload balanced (Majorana)
VAC
14:30 UTC Closing of SR tower (#68622 Erbanni, Francescon, Macchia, Pasqualetti)
16:30 UTC Beginning of vacuum pumping
17:20 UTC NI/WI cryovalves opened
Air Conditioning
SR clean air system recovery (Andreazzoli, Soldani)
During today shift, we permuted
- "rotor R16, box 01" with "rotor R30 box 04"
- "rotor R17, box 6" with "rotor R32 box 08"
with this change, we have R16 on WWN, R17 on WEN, R30 on NWN and R32 on NEN.
We took care to respect (and note) the rotor orientation at all positions. They are as follows:
- with respect to the rotor axis, the LED of the box is on the mirror side for NWN, NNF, NSF, WWN, WEN positions
- the LED is on the opposite site for NEN, NNN, NSN, WSN, WNN
We replaced the photodiode board, LED and box temperature probe for NCal box 04 which had a disconnected wire for the temperature probe.
In the NEB, we replaced the NCal "West" power supply (ID: 3629.6776.04-108784-Ls located at the bottom of the left rack) which had channel 1 and 2 "dead" by a new power supply (ID: 3629.6776.04-106682-Mm). This allowed to restore the NNN power.
we also checked :
- that the twist angles of the exchanged rotors were and still are at 8° with respect to the plates (see picture)
- the height of the "hat" of boxes 1 and 6 is 12 mm (see picture)
- box 4 and 8 do not have any "hat"
Injected signals from permuted NCals were adapated accordingly in NCalmoni and setdefault macros (set_NEB_default_lines.sh and set_WEB_default_lines.sh).
At the end of the operation, all 10 rotors have been successfully restarted at their nominal frequencies with injected lines slightly above 36 Hz.
I looked for an acoustic contribution of the INJ HVAC above 100Hz. Attached Figures highlight that there is a measurable contribution also above 100Hz, up to a few kHz.
The main effect is seen by the microphone LLR_MIC, which on Nov 27 2025 was positioned close to one air outlet (https://logbook.virgo-gw.eu/virgo/?r=67829). As a check, the second Figure shows similar spectra collected in the switch off performed on April 14 2025 (https://logbook.virgo-gw.eu/virgo/?r=66584), when the LLR_MIC was positioned in the middle of the INJ LAB (https://logbook.virgo-gw.eu/virgo/?r=65284). The result is the same.
Today I disconnected this accelerometer channel and removed it for the DAQ. The sensor is stil on the duct.
Note: standard cleaning of the chamber floor and Si_wafers installation.
ITF found in Upgrading mode for the SR diaphragm installation.
At 7:00 UTC started the planned maintenance; below the list of the activities communicated in control room:
- at 10:30 UTC the SAT team replaced the WI fan unit;
- NE/WE Ncal swaps (Mours);
- WR node removal (Bonnad);
- cleaning operations of the experimental areas;
- operations performed by the operator:
- TCS check and refill;
- TCS thermo camer reference;
- TCS power checks:
| CH [W] | OUTER RING [W] | INNER RING [W] | |
| WI | 0.35 | 0.255 | 0.035 |
| NI | 0.585 | 0.573 | 0.085 |
The other two main activities were SWEB measurements (Deleglise) and the intervention inside the SR tower (PAY team); both activities still in progress.
SBE
- SNEB loop opened by the guardian; properly closed at 13:17 UTC.
- SWEB loop left opened due to the activity still ongoing.
DET
The planned OMC lock and scan in single bounce has been skipped bacause of the intervention inside SR tower.
Starting at 9:15 LT some testing actions are performed in the fileserver machine. The only node involved is fs01.
These operations can cause glitches in the time interval between the start and end time activities.
- Performance testing started at: 9:15 LT
- Performance testing ended at: 12:10 LT
Today the main activity was on SR baffle: the SR tower had been opened in the early morning, the baffle dismounted, modified of reinstalled; the work inside the tower is still in progress..
Sub-system reportsSUSP
At around 8:50UTC, before starting with the work inside the tower I opened all the SR suspension control loops.
I tried to improve the automatic decomposition of Hrec, in order to adapt it to SR ALIGNED data. The aim is to have a not too arbitrary method of comparing the amplitude of the mystery components at different gps.
I started from October 2nd data, before the diaphragm installation. In order to correct evident discrepancies between data and fit, I built a specific 'irregular' component, reported in fig 1 as 'stray light'. After some iteration, in which the mystery noise slope has been assumed as a parameter of the fit together with the amplitude of mystery noise, readout noise and stray light, a slope of -0.55 has been chosen. In fig 1 also the frequency noise component is explicitly shown; this is not included in the automatic search of parameters, but it is a variable component. The variability depends from the different CMRF, monitored by the channel LSC_DARM_SSFS_LF_COUPLING. There is an initial assumption of noise level for a given CMRF, then the level is rescaled according to the actual CMRF. The initial assumption needs to be checked.
The automatic fit has been applied to recent good data, keeping the same slope of the mystery noise and the same shape of the stray light component. The accordance to the data is not too bad, as shown in fig 2. The new mystery noise level is 69 % of the old level. The new stray light level is 56 % of the old level. There is also a relevant change of frequency noise; the uncertainty of its estimation could affect a bit the estimation of the other parameters, but not too much.
