We attached two meggit accelerometer to the exterior of the SDB2 minitower chamber. Both accelerometers are attached at about 1.5m from the floor, in correspondence of the inner flange which supports the legs of the IP MultiSAS. The accelerometers are screwed onto an aluminum support which has been glued on the chamber vacuum vessel.

• ENV_SDB2_ACC_Z30 - horizontal, at about 30 deg from the beam direction (named Z) pointing outwards SDB2. This accelerometer is in correspondence of the resting point of one of the three IP legs (Picture 1)
• ENV_SDB2_ACC_X - horizontal, along the direction perpendicular to the beam (named X) and pointing in the direction opposite to Narm (Picture 2).

Looking at the spectrogram of Hrec since April 1st, we noticed an increase of a sideband noise around the 50 Hz during May 2nd-4th, Figure1 (top). It seems to be correlated to a decrease of accuracy of DIFFp_TX (bottom).

As in #64018, in Figure 2 we observe two couple of sidebands probably due to a beating between the 50 Hz and DIFFp_TX at  ±0.75 Hz and ±0.42 Hz (roughly).

A residual of these sidebands seems often present: purple curve of Figure 2 and spectrogram in Figure 1.

We performed some measurements with a portable magnetometer: 3-axial magnetic probe FL3 100 Stefan Mayer. 

Figure 1 compares spectra recorded in two locations:

• "EXTMAG chs X,Y,Z" the probe was placed on the soil nearby the buried external magnetometer
• "GUARD3 chs X,Y,Z" the probe was on the soil next to the vent tube of the methan gas pipeline, this is located inside the EGO fence next the EGO guardiania, see the attached pictures.

The GUARD3 spectra clearly show the noise: 0.23 Hz spaced lines peaking at 8Hz. The peak amplitude (spectra are obtained with 25s window) is approx 2 nT/sqrtHz. Which is a factor approx 100 larger than measured in the location EXTMAG, but similar to that measured by the magnetometers on the NI and WI tower base. Might be due to telluric currents in the chambers?  

As a check of the probe calibration, in Figures 2 and 3 we compare the EXTMAG measurement with that of the buried magnetometer, ENV_EXT_MAG_N. The fluxgate probe is more noisy (intrinsic noise) but around 8Hz they are measuring the same.

The indication is that the magnetic disturbance is radiated from the methan gas pipelines. A noise clearly associated to the power supply for galvanic currents in these pipelines was observed in the year 2022 (55542 and 57973). At that time the noise was shaped as approx. 5Hz comb. 

Federico has contacted the methan gas company (SNAM) to investigate further the source.

Today also FIAMM01 (Carabinieri) had some flyover near CEB (08:40 UTC)

The estimated distance is ~ 200m, the height was ~ 200m (credits: flightradar24), well inside the NOTAM area.

The signal is very clearly visible in the CEB microphones. The ITF was unlocked (maintenance).

We have removed the temporary magnetic and seismic probes from the DT turbo, placed there on Feb. 24.

We placed the magnetic probe onto the MC tube (similar location where it had been in the past). The acquired channel is perpendicular to the tube (probe "X"). We used the same name: ENV_CEB_MAG_MC_TUBE.

Glitches disappeared around 6:45 UTC. Has some action been taken? Indeed, square waves were seen also in the CEB UPS CURR T monitor, as for the old problem with WI heating belts that Bas pointed out.

A new noise is seen in the external magnetometer starting April 22 19:56 UTC. Figures 1 and 2. The noise has been detected and studied by Renato and Federico. Here is a report of the investigation so far.

The noise is impulsive, as seen in Figures 3,4,5. Observed in the time domain it consists of a carrier at about 8Hz switching on-off with a cycle of approximately 4.4s (0.23 Hz): on for 2.2s and off for 2.2s.

The noise is seen by all magnetometers site-wide. Internal magnetometers sees it a factor up to about 10 larger than the external "N" magnetometer, in Figure 6 and Figure 7 (the EXT_N magnetometer is the gray spectrum in all 3 plots). Magnetometers that see it a bit more intense are those close to NI, WI and WE towers.

A close look to the narrow spectral structure of the noise shows that it does not follow the mains, in Figure 8.

These hints suggest a DC-powered PWM source (Federico).

Bruco runs using ENV_NI_MAG_V as target, and EXCLUDING all magnetometers (ENV_*MAG*) channels, show that this disturbance is not coherent with any other ENV channel (https://scientists.virgo-gw.eu/DataAnalysis/DetCharDev/bruco/users/fiori/ENV_NI_MAG_V_1397853318_ENV/) with the exception of a small coherence with the ENV_CEB_ELECTRIC. In particular no coherence, nor evidence of the noise is seen in all IPS and UPS probes. No coherence is also measured with any other Virgo signal (https://scientists.virgo-gw.eu/DataAnalysis/DetCharDev/bruco/users/fiori/ENV_NI_MAG_V_1397853318/). While s is a good news for the interferometer, it does not help much locating the source.

Measurements will be done also to check for possible external sources, like it was for galvanic currents in the natural gas pipelines (https://logbook.virgo-gw.eu/virgo/?r=55542).

As observed by Federico, the metronix magnetometer in MCB is having an issue starting from 2023 October 2 UTC 00:03:03 (Figure 1). The signal looks corrupted (Figure 2).  This does not seem an issue with the ADC and neither with the driving electronics, since other channels sharing the same boards are fine. We will investigate further at next maintenance.

This fauty condition was not signalled by the DMS DeadChannel since the associated rms was smaller than the set threshold. The rms threshold has been updated (0.35 to 1 nT) and this channel temporary shelved.

This is a first (preliminary) look at the effect of acoustic injection into Hrec, performed on Thursday 18.

For each injection (at the 0.03, 0.04 and 0.05 V levels) the BNS range decreased.

Here the entire Hrec range from 10 to 1000 Hz.

There are regions growing at low frequency (around 120 and 170 Hz) and high frequency (the most relevant from 500 to 540 Hz).

Below 100 Hz nothing seems to have changed significantly.

This site Elian suggested: https://www.flightradar24.com/ keeps records of aircrafts tracks.  Specifically, this is the helicopter that was flying near us on April 18 and 19: https://www.flightradar24.com/data/aircraft/mm82053.  Position and time are provided,  so is possible to locate its position at a particular time. Data are kept for 7 days. In particular its track of April 18 afternoon (attached shapshots) maybe passed a bit closer than 2000ft from CEB and NEB.

We tested the sensitivity of the top-stage BS accelerometers at three different levels of acoustic injection (nominally 0.03 - 0.04 - 0.05 V).

• Pink = no noise, Orange = 0,03, Green = 0.04, Grey = 0.05, Blue = narrow filter

Noise was filtered from 8 to 2000 Hz, but the actual noise produced was only from 20 Hz and up, as the speaker is unable to go lower.

The fourth injection (18:04:40 UTC - (80 -100) Hz, 300 sec, 0.04 V) aimed to produce the same level around the frequency of ~93 Hz (without generating out-of-band noise) where one of the horizontal BS F0 accelerometers (Sa_BS_F0_ACC_H3_500Hz) is usually excited during acoustic injections, in order to check whether the coupling is linear or not.

• Blue = no noise, Green = narrow noise, Pink = broadband noise

Unfortunately, the filter was too narrow, and the noise spectral density at 93 Hz was lower than expected.

However, we can say that generating a higher level by a factor of 2 (with no noise at lower frequencies) resulted in an increase of the peak by about a factor of 2 (difficult to estimate accurately). It appears that there is no upconversion and the system is "linear."

During this test we also noticed that there is some (unexplained) coherence between the upper stage F0 accelerometers and the lower external magnetometers (this is also the case in other towers besides BS).

At first glance one might think of general coupling due to the external accelerometer cables running not too far from the magnetometers (as indeed they are), but there are high-level signals in the acceleration spectrum that have no coherence. If it were a coupling from the cable, it should be broadband.

Indeed around the time of the unlock (yesterday 15:22 UTC) there has been also an earthquake (M 5.6 - 9 km W of Sulusaray, Turkey, 15:11 UTC)

The unlock was likely due to it, as reported by A.Magazzu in https://logbook.virgo-gw.eu/virgo/?r=64020.

This makes difficult to disentangle if there has been aslo an impact from the helicopter.

Yesterday an helicopter was seen flying close to the Virgo buildings. This was in the late morning but the ITF was not locked. And again in the afternoo (14:30 to 15:30) when the ITF was locked.

Some indication of the passages are in the first plot, showing the RMS of some microphones in the band around 50Hz.

Helicopther noise is seen also at NEB and WEB. The sound signal is visible the band up to 200Hz, louder around 30 Hz (this can bee seen in Figure 2).

To a first look no evident glitch is seen in Hrec.

Yet, the unlock (around 15:20) is associated to scattered light arches in hrec and in B8 photodiode. At that time, judgeing from the sound level in microphones, the helicopter was close to WEB.

A correlation of the two events is possible (Figure 3).

But I would advise a better look with more accurate tools.

We performed a set of four acoustic injections in CEB with the AcousticInjectionCEB VPM process:

1) 17:07:55 UTC - (8 - 2000) Hz, 600 sec, 0.03 V

2) 17:21:05 UTC - (8 - 2000) Hz, 600 sec, 0.04 V  (25 min glitch at ~17:29:24 UTC)

3) 17:33:48 UTC - (8 - 2000 )Hz, 600 sec, 0.05 V

4) 18:04:40 UTC - (80 -100) Hz, 300 sec, 0.04 V

The directory path of output files is /virgoData/NoiseInjections/AcousticInjectionsO4/output. The list of file injections is reported below:

1) AcousticColored_NOISE_CEB_DetTerrace-1397495261.txt

2) AcousticColored_NOISE_CEB_DetTerrace-1397496052.txt

3) AcousticColored_NOISE_CEB_DetTerrace-1397496814.txt

4) AcousticColored_NOISE_CEB_DetTerrace-1397498666.txt

As Piernicola confirmed, the sidebands at 46.7 Hz and 53.3 Hz are the beating between 50 Hz and DIFFp_TX line at 3.3 Hz (purple curve).
Indeed, when the DIFFp_TX line was set to 4.8 Hz, there were two sidebands at 45.2 Hz and 54.8 Hz, respectively (blue curve).

Looking at the spectrogram of Hrec, we observed a peak at 47.5 Hz which arose on April 15th, ~01:00 UTC (between two locks), see Figure 1 and 2.
It could be related to the F7 crossbar mode of the NI tower that we measured by magnetic injections to be at 47.65 Hz (VIR-0300A-24).
In this case, it seems that the line has shifted slightly in frequency.

Transients are see also in DET B8 DC (Figure 1). Signal SBE_SWEB_F0_z_LVDT_500Hz converted into velocity and low pass filtered (fcut 0.5 Hz, in order to remove large high frequency noise in this signal) seems to reproduce sufficiently well the shape: Figure 2. Also the second order of arches (weakly seen in the photodiode)  is similarly reproduced doubling the velocity, although not plotted.  Maybe there is a better signal to use that measure the bench motion?

On April 9 we performed a set of short (60s) colored acoustic injections in the CEB. The ITF was locked in LOWNOISE 3 since a few minutes.

The purpose was to tune the level of the injection in such a way to avoid triggering the 92 Hz oscillation of the BS F0 accelerometers (mostly Sa_BS_F0_ACC_H3) which caused unlocks in the past (https://logbook.virgo-gw.eu/virgo/?r=63709). The purpose of the present test was not to understand the nature and physical reason of the oscillation onset, which remains to be understood.

We injected colored noise between 20 and 2000Hz with 3 levels: 0.03 V, 0.04 V and 0.05 V, one 25min glitch occurred right at the beginning of the 0.05 V injection (Figure 1).

The intensity on the acoustic noise produced in the hall, measured in the position of the hall microphone, was of the order of a factor 20 above the quiet condition (Figure 2). The 92 Hz oscillation of  the BS F0 ACC H3 accelerometer onsets already with the 0.03 V but  amplifies x5 and x10 when the injected level increases from 0.03V to 0.04V and from 0.03V to 0.05V, respectively (Figure 3).

Figure 4 shows the impact on hrec. The noise in hrec increased at some structures, mostly known to be associated to SDB1. These excitations are well visible with all injected levels (Figure 5, which also shows the 25min glitch).

It seems to notice also an increase of the 74 Hz line (DARM loop gain) and the 227 Hz line (SSFS loop gain). As well, it seems to notice a small increase of the noise in the bucket. It seems that particularly the injection at 0.05 V, brings the ITF to a different working point where other noises (e.g. frequency noise) are more coupled.

However, spectrograms in Figures 6 and 7 indicate that the amplitude of 74 Hz and 227 Hz lines was not so stable during the injection period (we were at the beginning of a lock) and its correlation with single acoustic injections is not straightforward.

Paolo's suggestion is to better study this behaviour with longer injections.

The issue with the extra spike at the beginning of the colored noise injection was related to time settings in the ACL commands in the ENVnoise process. These modifications were made by Alain (on March 26):

Figure 1 shows the result of the test: blue is with the OLD settings, purple is the with the NEW settings (the same colored noise with amplitude 0.025 V has been injected in both cases). The spike is no longer present.

The same test was done by injecting the colored noise from the ENVnoise and also using the ENV_MAIN node which calls the AcousticInjectionCEB process.

The increased coherence with ENV_NEB_IPS_CURR seems associated to the accidental presence of a glitch in hrec (one of the 25-min glitches) and a glitch in the ENV_NEB_IPS_CURR sensors.

The two glitches are NOT coincident indeed but a few sec away (the IPS glitch occurs after), but they both fall in the 10s window of the Bruco computation.

Figure 1: coherences are computed 120s before the glitch (purple) and in a 120s window containing the glitches.

Figure 2: spectrograms show that the two glitches are a few seconds away. The COHETIME plot implemented in dataDisplay measures a sort of "anti-coherence" (the coherence goes to a lower value in the time window that contains both glitches).

It is not clear what is peculiar to the NEB_IPS_CURR sensor glitch to produce coherence with Hrec?

Today we have concluded the tuning of DMS threshold for a few ENV channels which have been observed to fluctuate between green and red inside the DeadChannel monitor.

• ENV_EQB2_ACC_Y,  old value 1E-4.   ----> new value 1E-5
• ENV_EQB2_MIC,  old value 6.5E-3  ----> new value 1E-4
• ENV_IB_CT_FINGER_ACC_Y, old value 1.5E-3 ---> new value 1E-4

In particual for channel ENV_IB_CT_FINGER_ACC_Y we had to first fix the issue with too large 50 Hz and harmonics. The same problem was obseved in the past 62620 and fixed by replacing the BNC to lemo adaptor. Figure 1 shows the spectrum of the accelerometer powered off (blue) with the old connector, and Figure 2 shows the same with the new connector.  Figure 3 shows the procedure followed for setting threshold for the sensor ENV_IB_CT_FINGER_ACC_Y.

On Friday afternoon, while checking the power supply of some accelerometers on the DET terrace, we noticed that the flashing yellow light of the LargeCoil was ON. Indeed, the power amplifier was ON (but without any signal sent from the DAC).

Trying to turn it OFF via the Process Online Monitoring page, we found the LargeCoil_CEB gray (NEB and WEB were correctly green). The process could not be restarted. The box remained gray and the relay powering the amplifier remained in the "1" state.

Today I tried again from remote and the process restarted. I turned off all the relays at 10:51:10 UTC - There is a huge spike on the monitoring channels (ENV_CEB_MAG_COIL_CURR_MON and ENV_CEB_MAG_COIL_VOLT_MON), but it is a fake signal due to the fact that these signals are coming from the power amplifier that turned off (nothing is visible in the CEB magnetometers and in Hrec).

We will check the system again during commissioning (Monday afternoon), also because it seems that the status of the relays visible to the right of the green box is always zero, even though they are (really) set to 1.

Extra hrec noises were present during tonight locks (Figures 1 and 2):

• a broadband noise up to 100Hz
• a bump around 43 Hz

We do not know it the two are related.

Investigating we found that the PSTAB0 line at 43 Hz is injected. and it is seen in various INJ signals (Figure 3).

The plan is to try to switch it off after locking and check the impack on hrec.

This is a follow up of https://logbook.virgo-gw.eu/virgo/?r=63649

Friday afternoon we used two hours of commissioning to test the ENV_MAIN metratron node. The ITF was locked in LOW_NOISE_3_SQZ, COMMISSIONING.

WE performed this sequence of environmental injections:

• magnetic injection far field in CEB with the wall coil: 300s, sweep 8 Hz to 1000 Hz, 9V to the DAC
• magnetic injection far field in NEB with the wall coil: 300s, sweep 8 Hz to 1000 Hz, 9V
• magnetic injection far field in WEB with the wall coil: 300s, sweep 8 Hz to 1000 Hz, 9V
• acoustic injection in the CEB  with the loudspeaker positioned in the DET terrace: 60s colored noise 8 - 2000 Hz, 0.025 V to the DAC

The magnetic injection was succesfully performed at CEB, NEB and NEB (Figure 1). The 9V amplitude although close to the limits for current (6Apk) and Voltage (70Vpk) did not saturate the amplifier (Figure 2). With this amplitude the signal is seen sufficiently well in hrec for NEB and WEB up to about 100Hz. For CEB the signal in hrec looks not so loud (Figure 3) but we might gain a bit by doubling the injection time to 600s. For NEB and WEB the Bartington magnetometers ENV_NE(WE)_MAG_V,N,W placed close to the NE(WE) tower have to be used for the coupling function computation,  because the metronix magnetometers on NEB and WEB saturate for the low frequency part of the sweep.

The output files were successfully produced in the designated directory: /virgoData/NoiseInjections/MagneticInjectionsO4/output/ and /virgoData/NoiseInjections/AcousticInjectionsO4/output/

One thing that is useful to be implemented in is that once the sweep injection is concluded a few seconds are waited before switching off the amplifier.

Instead the acoustic injection did not preform as expected because the large spike noise at the beginning of the injection appeared again (!) and of course unlocked the ITF: Figure 4

Indeed, to our understanding this should not have happened since the used

/virgoDev/Automation/userapps/ENV_MAIN.py

now points to the patched version of the code (v2r1p1), which when tested by launching the AcousticInjectionCEB process from the VPM performed ok (i.e. no spike)

.... reading from the ENV_MAIN.py:

#        noise_injection_script = "/virgoDev/EnvSwepts/v2r2/Linux-x86_64-CL7/bin/AcousticColoredInjection-conda /virgoData/NoiseInjections/ENV/AcousticInjectionCEB.cfg"
        noise_injection_script = "/virgoApp/EnvSwepts/v2r1p1/Linux-x86_64-CL7/bin/AcousticColoredInjection-conda /virgoData/NoiseInjections/ENV/AcousticInjectionCEB.cfg

We need Franco or Rhys to have a look into this.

This hrec bump seems to be the aliasing of the bump laying between 1.5 and 1.1 kHz which is visible in the Audio_100kHz channel.  ... to be found :-)

But that means that all ENV sensors are blind.

By the way the same happens for the hrec lines at 9877 and 9881 Hz, actually at 10119 and 10123 Hz.