*** Mechanical Transfer Function Measurement of the NI Instrumented Baffle ***

Today, mechanical transfer function measurements of the NI instrumented baffle were performed. The instrumentation, data acquisition system and excitation setup are described in the previous logbook entry [elog 69222]. The instrumented baffle was excited using the (big) shaker installed on the tower base.

The single reference monoaxial accelerometer was sequentially moved among three different locations within the NI tower, shown in Figure 1 (first pdf file):

• R1: horizontal mounting position below the instrumented baffle;
• R2: vertical mounting position located close to the instrumented baffle;
• R3: horizontal mounting position on the vacuum vessel.

Figure 1 shows the three reference locations together with close-up views of the sensor installation. 

The triaxial accelerometer was mounted directly on the instrumented baffle and moved between two different locations during the measurement campaign. The upper and lower accelerometer positions are shown in Figure 2 (second pdf file).
The sensor was attached using a custom adapter manufactured by the IFAE group. Due to the threaded mounting, the final orientation of the sensing axes was determined by the thread engagement and could not be precisely aligned with the nominal vertical-horizontal reference frame.

The resulting sensor orientations were:

• Top position: x-axis aligned with the cable direction, z-axis aligned with the adapter axis.
• Bottom position: x-axis aligned with the cable direction, y-axis aligned with the adapter axis.

Figure 3,4,5: Measurement configurations with the accelerometer mounted in the upper position of the instrumented baffle. The three figures show the corresponding locations of the reference accelerometer: R1,R2,R3, respectively.

Figure 6, 7, 8 : Measurement configurations with the accelerometer mounted in the lower position of the instrumented baffle. The three figures show the corresponding locations of the reference accelerometer: R1, R2, R3, respectively

The measurements were performed before the installation of the flange baffle, in order to access the instrumented baffle structure directly.

The analysis of the acquired data will follow.

R. Cavalieri, F. Nocera

while inspecting the NE Ring Heater Power Supply (entry 69238)  we noticed that the PCal Laser Power Supply (?) unit (see picture) has an ominously noisy fan.

I would suggest to have it checked/swapped with a spare.

The calibration is done for the displacement at the stabilized point : the entrance of the EOM.
For the shift, the vertical one was quite clean and gave a calibration of -1900 (V/V)/m, which means 526 um/(V/V) (plot 1)
For the horizontal shift, it was not as clean as the vertical one (plot 2), we might need to redo it. For now we decided to use the same calibration than the vertical one since they are not supposed to be different. 

Then we did the calibration of the tilt by using the PZT on EIB (plot 3 and 4) 
We know that the PZT has a dynamic of 3.5 mrad for 140 V, we did a scan of 3 V and found extreme values of 0.39 V/V and -0.73 V/V on Vnorm
We found 3.5e-3/140 *3/(0.39+0.73) = 67 urad / (V/V)
Similarly we found 68 urad / (V/V) for the horizontal. 

We added the calibrated channels to ACL. 
The results with the loop closed is showed in plot 5 and are quite in agreement with what we were expecting : few nrad and few nm of residual noise. 
We keep the loop closed to monitor is long term behavior

R. Cavalieri, F.Nocera

we went to the NE and inspected the Ring Heater Power Supply and its cabling.

There is nothing special to say: it is a commercial device with a regular, *non-locking* power input connector and it uses a commercial 3-wire AC power supply cord (CEE 7/7 Plug to IEC 60320 C13 Power Cord, if you are interested in this sort of details).

If left alone, it does its job nicely.

During the NCal activities yesterday, the NE RH was accidentally switched off (see Fig. 1).

Benoit reported the presence of a loose cable in the RH electronics chain. Therefore, today Flavio inspected the system to investigate the issue and verify the cable connections.
Following the inspection, the RH was switched back on at 14:23 UTC with the voltage set to 16.6 V.

Schedule: finalise installation of NEN and NWN, rearange all cablings

15 June 2026 : Start installation around 15:00 utc

• Position adjustements for NEN setup:
  • Adjust zero positions with jig for North East setup in /virgoData/VirgoOnline/SNEB_dbox_rack.cfg:

    	NEF lateral	NEF Vertical	NEM Axial	NEM Vertical	NEN Lateral	NEN Vertical
    Old values	-7.661	-7.03	7.435	8.225	7.954	7.306
    New values	-7.1195	-6.7015	7.1135	6.607	6.651	7.06

  • Mean of sensors values now 0 within 1 micron precision.
  • Remove jigs and align setup to better than 0.05 mm (see NEB_EastSetupAlignment histograms)
• Position adjustements for NWN setup:
  • Adjust zero with jigs in /virgoData/VirgoOnline/SNEB_dbox_rack.cfg :

    	NWF lateral	NWF Vertical	NWM Axial	NWM Vertical	NWN Lateral	NWN Vertical
    Old values	7.05	-7.12	-7.753	6.7530	-8.035	7.063
    New values	6.777	-6.9343	-6.9823	6.7602	-6.9060	6.7322

    Means of sensors values below 1 micron now

  • Remove jigs and align setup to better than 0.05 mm (see NEB_WestSetupAlignment histogram)

• Position adjustements for NSN setup:
  • Adjust zero with jigs in /virgoData/VirgoOnline/SNEB_dbox_rack.cfg:

    	NSF Lateral	NSF Vertical	NSM Axial	NSM Vertical	NSN Lateral	NSN Vertical
    Old values	-7.444	7.619	-7.361	-7.691	7.004	-7.764
    New values	-7.0234	7.2171	-7.0236	-7.3403	6.4019	-7.3625

    Mean sensor values below 3 micron now

  • Night pause...Continue on June 16th (7:00 utc)
  • Remove jigs and align setup to better than 0.05 mm (see NEB_SouthSetupAlignment histogram)

At the end of the intervention we have :

Box 2021-08 (R4-32) on NSN with LED "away" from mirror

Box 2024-12 (R4-12) on NEN with LED "away" from mirror (and generating loop attached)

Box 2021-04 (R4-30) on NNN with LED "close" to mirror

Box 2024-10 (R4-10) on NWN with LED "away" fro mirror. It produces more accoustic noise than the others

The rotor cables for NWN have been installed

All rotors have been tested during few minutes at 50Hz.The difference in acoustic noise between the NNN and the others was less noticeable than at the nominal frequency.

All microphones gain have been set to 40dB (East and West setup were at 60dB. South was at 40 dB... We don't remember for North).

All temperature sensor gains have been adjusted to follow the new cabling on the DAQ boxes.

NB: During the NCal  power supply reshuffling, we touched the ring heater power supply connector and the power supply switched off for a short time (on 15 June 15:30 UTC). Ring heater experts will come to check.

This afternoon we started to work on the calibration of the BPL. 
We used a substrate in fused silica which thickness is 10 mm and placed it after EIB_M1c at around the same distance than the EOM entrance (the point to be stabilized). This corresponds to about 12.5 cm from PZT2.
Then we rotated it both around the X and Y axis in order to induced a known shift towards the QPD. 
The plots are attached to this entry. We will analyze it in details tomorrow. 

ITF found DOWN in UPGRADING mode.

Below the list of the activities communicated in control room:

• NI instrumented baffle installation - https://logbook.virgo-gw.eu/virgo/?r=69224
• removal of the WI baffle - https://logbook.virgo-gw.eu/virgo/?r=69225
• in the afternoon the INJ team worked at BPL calibration

Preliminary measurements

On June 10 and 11 we installed the setup and performed preliminary measurements in order to check the instrumentation and optimize the measurering setup.

We installed two shakers on the exterior of the NI chamber: the large shaker is placed om the NI tower base, NW corner, and the small shaker clamped to the North big flange (thank you Antonio for helping in this installation). The shakers (in turn, manually) are connected to the amplifier which is driven from a DAC ch in the TCS room.
After a careful cleaning of all the tools, we moved inside the NI.

As a test we performed measurement of mechanical modes of the the frame shown in Figure 1. We used the monoaxial accelerometer PCB352C68 on the vacuum chamber (attached with double tape, which Antonio aknowledged, asking for a careful cleaning with Acetone) and the triaxial accelerometer PCB356B18 ("golden cube") attached to the frame in different positions, aslo with double tape. For the data acquisition we used the CoCo80X.

We tested (the full set of measurements is detailed in the attached .txt file):

• injecting different levels of colored noise 10-1200 Hz to the shaker (0.02,0.03,0.04 V). For reference, inside ENVnoise.cfg:
  ACL_NOISE_CH                noise_white            "V"     5    SAMP_FREQ    1.0
  ACL_FILTER_CH                noise_colored        "V"    5    SAMP_FREQ    noise_white    0.03    "flt3"
  and inside ENVnoise_Filters.cfg:
  ACL_FILTER_SET         "flt3"             1 1 600 20          # -->  sets gain 1 @ f0 Hz (must be the same f0)
  ACL_FILTER_BUTTERWORTH "flt3" "bandpass"  4 3 600 590
• use of the small or the big shaker
• two configurations for the monoaxial acc: vertical or horizontal (see pictures)
• two positions of the cube acc. on the frame: (1) inner ring, (2) outer ring close to holding point

For each configuration we measured the TF of the monoaxial acc versus each axis (X,Y,Z) of the gold cube acc, and compared.

Figures 1-3 are pictures of the frame with accelerometers in different positions.

Figure 4 compares spectra during quiet and during shaking. The shakers were able to excite above the quiet noise in the whole expected range.
Figures 5-9  refer to the setup with monoaxial acc. horizontally placed on the vessel and the cube acc on the inner ring of the frame. They show: spectra, coherence, TF between monoaxial acc and each of the three direction of the cube acc.
Figures 10-end is the same set, but when the cube acc. was positioned on the outer ring of the frame, near to the frame's holding point.

Measurements were satisfactory, the setup works. 
A number of peaks were excited especially in the range 50Hz to a few hundred Hz. Good coherence is measured in this range.
TFs look satisfactory: we observe phase rotation in correspondence of the main excited modes. The red points in the TF plots correspond to coherence > 0.4.

Moving the cube accelerometer from the inner to the outer ring of the frame, some peaks are no longer excited (for example the 130Hz peak is no more observed). As expected, this position is more rigid and low frequencies modes are not easily detectable from here.

Additional observations:
Tests indicate a slightly better preference for using the small shaker, with level 0.03V. The placing of the accelerometer on the vacuum chamber, horizontal or vertical, does not make significant difference in the measured TF. 

Between May 29 and June 3rd we performed at 1500W noise characterization measurements of two ion pumps, which here we call simply small and big (info on the exact model will be added later on). These pumps consist of a large permanent magnet and the concern is the magnetic noise produced when this pump vibrates withing the static Earth field. A question concerning this noise and the consequent safe distance from the O5 test masses was asked by VAC reviewers. Answering it is the aim of this activities. Two activities have been performed.

1) Mapping. 
This activity was lead by Gilles who measured the ion pump static field on 3D grid of positions around each pump. For the small pump he used a 2D paper grid, for the big pump he used the plastic perforated frame that INGN-Genova made for the payload magnetic characterization and which the vacuum team moved from the CEB clean rooms to 1500W and reassambled in position. Gilles used his 3-axial magnetic probe, moved along the grid.

Attachments 1 and 2 show pictures of the setup of the big pump.

2) Shaking.
The big pump was excited using a little hammer tapping on the top flange of the ion pump, while one accelerometer (meggit) positioned vertically on top of the pump, and one 3-axial magnetic probe (Bartington MAG03_MC_100) were recording respectively the vibration of the pump body and the magnetic field. The magnetic probe was moved at a number of distances from the pump edge (approx 20cm to 120cm). Figure 3 is a sketch with coordinates of the measuring grid.
The attached txt file lists all measuring times and associated position of the magnetic probe. Attached are also spectrograms of the full measurement set. A magnetic field noise excess was measured in all locations. The last two show the probes spectrum when at approximately 30cm from the pump edge (mag probe position J13). The excess magnetic noise is evident and is also coherent with the vibration. 

Data frames have been saved in /data/procdata/envmon/MagneticNoise/ion_pump/shaking/saved_gwf/ion_pump_shaking_20260603_1464522918_8500.gwf

Analysis will follow.

ITF found DOWN in UPGRADING mode
No activities communicated to the control room

Today around 14:00 UTC, the WI PAM was moved back to its original reference position marked on the alignment plate (see 69208), since it was temporarily moved to allow the replacement of the damaged ZnSe viewport (see 69219).

ITF found DOWN in UPGRADING mode.
All times are UTC.
Below the list of activity comunicated to the control room:
09:03 - 09:56 Gouaty went in CEB Storage Room at 2nd floor, no access to any experimental areas required.
10:10 - 10:39 ZnSe WI viewport inspection (Pasqualetti, Nardecchia, Lumaca, Corubolo).
14:16 Zaza reported that NI payload has been cleaned and the ZnSe viewport has been replaced.