This morning, from about 7:40 to 8:10 UTC we performed a measurement of the magnetic noise in the rack hosting the environmental monitoring electronics in DAQR, in different conditions:

- at about 7:42 UTC the probe was placed in the selected position, between the ENV-NI and ENV-BS slow monitor modules;

-at 7:51 UTC all the envmon electronics in the rack was switched off;

-at 8:00 the two PCB amplifiers were switched on;

-at 8:02 the Nexus amplifier was switched on;

-at 8:04 the slow monitoring modules far from the magnetic probes (ENV-IB,PR,DT,SR,WI) were switched on

-at 8:06 the remaining modules were switched on.

In figure 1 the evolution of the measurement is shown, while in figure 2 the spectra of the noise measured in different period of the test are reported: magenta=All OFF, cyan=PCB and Nexus ON, green=Far modules ON, blue=All ON.

It is evident that the measurement is mainly dependent from the distance between the probes and the source, indeed about a factor 10 of noise increase is observed between the two last conditions.

The mentioned o-ring has been replaced, the SR tower bottom access flange is now open.

Venting of SR tower has been started.

He-test main results:

• the newly added viewports #U59 , #H54 (logentry 49041) have passed, LR<5E-8 mbar.l/s
• the 2nd virola viton o-ring is to be replaced

I have fitted by eye with Gaussians the scattered light bumps for which we have some understanding based logbook 48854 and logbook 47928,  and the taken into account the expected change in scattered light coupling between O3 and O4 due to SR installation. I haven't included the known bumps of scattered light from squeezing. As these should disappear with the installation of SQB1 and having the double Faraday isolator suspended under vacuum.

Figure 1 shows as the dashed cyan curve the total of the scattered light bumps modeled. This is implemented in GWINC, and the measured parameters in O3 are in the snippet of code below.

In total for O4 these bumps would cause a 4 Mpc loss of sensitivity (from 108 to 104 Mpc). With 3 Mpc lost due to the 33Hz bump from SNEB, and roughly 1Mpc lost due to each SWEB (125Hz), SR-DET link (180Hz) and SIB1 (101Hz and 157Hz) (remember Mpc add in quadrature).

The loss is not that big, because most of these bumps are relatively narrow, but they might be more broad band scattered light structures that are harder to see but have a bigger effect on the data.

% scattered light from SWEB
bump125Hz = SWEB.*sqrt(1.13^2-0.9^2)*1e-23.*exp( -(f-125).^2/4^2);

% scatter light from SR-DET link
bump180Hz = SDB1.*sqrt(1.8^2-0.9^2)*1e-23.*exp( -(f-180).^2/1.7^2);

% scatter light from SIB1 vacuum chamber
bump101Hz = SIB1.*sqrt(2.7^2-0.9^2)*1e-23.*exp( -(f-101).^2/1^2);
bump157Hz = SIB1.*sqrt(1.6^2-0.9^2)*1e-23.*exp( -(f-157.4).^2/2^2);

% scatter light from SNEB vacuum chamber
bump15Hz = SNEB.*2e-22.*exp( -(f-15).^2/5^2);
bump33Hz = SNEB.*2.2e-23.*exp( -(f-33).^2/5^2);

After the recent repair/mitigation attempt on the BS IVC, the BS tower has been put under vacuum and then tested in order to re-estimate the residual ‘leaking defect’ through the IVC.

The test has been done by injecting the He gas inside the tower upper part (via Vc2, CL 6.6E-7 nom.) and measuring the He flux reaching the lower part (and then the upper too) by the usual Leak Detector.

The IVC ‘leaking' defect is estimated around  ≈ 3 x the expected figure (while before the intervention the estimate was > 10 x ).

A significant reduction has been achieved.

Here some recordings:

Before the repair: LD_old lower =7.2E-8 A.U.

After the repair run I: LD_old lower =1.1E-8 A.U.

After the repair run II: LD_new lower =1.4E-8 A.U.

test pressure 1E-5 / 1E-6 mbar; 400/547Hz

PR tower: LD_old lower = 0.5E-8 A.U. (for comparison)

Additional note: we have rechecked the leak tightness of the tower upper rings (opened/closed for the intervention). No leaks found above > 5E-8 mbar.l/s.

In conclusion: the defect has been localized and a significant mitigation has been accomplished. We consider the intervention completed for the moment.

Also, we shall prepare for a more reliable a repair,  to be implemented when needed or convenient for the general plan (normally a new suitable seal replacing the present one found leaking, suitably shaped. It will require to raise the IVC by some mm during the installation).

Today we tracked the position of the SQB1 microtower (11.3000, 3.3100) on the floor of DET Lab (Fig. 1 and 2) and the other auxiliary points neded for the next installation of the clean air structure (Fig. 3, 4 and 5).

With the payload completely assembled we have finalized the cabling of the new devices: Ring Heater and its temperature probe.
From the "eletrical point of view" it has been all checked and tested.

Following the installation of a new ‘viewport’ (shall be reported separately) today the NE minitower has been evacuated and the new parts have been He-tested for leaks (DN350CF + relevant small viewport).

Result = No leaks found on the new parts (Detector range < E-5 mbar.l/s , estimated)

Today the bottom part of the SR tower has been cleaned in preparation of the PAY integration.

A vacuum cycle has been started too: we shall perform some He-test activity and then will re-vent the tower within friday this week.

Yesterday the installation of the GNSS permanent station at EGO site has been completed and started.

The station is part of the "Nuova Rete Fiduciale Nazionele GNSS dell'Agenzia Spaziale Italiana". The reference point is labelled VIRGO00ITA.

Here attached some pictures of the installation (Fig1 to Fig5).

Today we tracked the positions of the holes for fixing the rails on the ceiling of the DET Lab, after opening the upper part of the metallic platform (Fig.1 and 2).

From Monday to Wednesday morning we dismounted the acoustic enclosure of the external squeezer bench (fig6) and stored in 3 pallets on the south terrace (fig4,7). The external squeezer bench (fig1,2) has been movemented with the Transformer system and carts and stored on the east terrace (fig3,7).
The SQZ area of Det Lab is now free (fig5).

The temperature inside MC building has rised to about 25 degrees in environmental probes, after a fast rise it seems to have reached a plateau.

Looking at HVAC monitors and IPS current monitors (see Figure) the HVAC system (heaters and chillers) seems to have stopped around 13:20 UTC.

It can be related to the test that was started this afternoon of putting the MCB on a local electrical neutral.

Davide has been contacted. Yet, the situation seems not crtitical and can probably wait till the morning. Having reached the maximum the internal temperature will not increase more during the night.

This morning the in-vacuum cabling, necessary for the electrical connection of the Ring heater, has been restored. In particular, the in-vacuum cable (labeled "U") dedicated to it , has been reconnected to the feedthrough on the S-W flange.
The cable, installed at the time of AdV and reserved to the payload connection, was "temporarily" unplugged in December 2017, to allow the connection of cables for  Integration of inertial platform prototype in SR tower .

To allow this task, today the tower has been purposely opened and then closed again by the VAC team.

Suspension controls have been opened and electronics turned off at SDB1 to allow the scheduled intervention on the cabling.