Today around 12:40 UTC I have scanned the bench in TY and in X with the OMC shutter open, to see if the beam transmission is much higher on the right side of the B1s camera where there is a bright spot on B1s in LN2 (Figure 1). This could be the case if for example that part of the beam was passing next to the coating. I haven't seen any brightening when trying to put the MICH flashes beam through that spot. Actually that is the place where the beam starts to be clipped and stops reaching the camera. So it is unlikely that the bright spot vislbe on the right edge of the B1s beam is due to a higher transmission of light through the B1s beam splitter at that location.

I ve compared the main signals in three configurations;

- October 12 (before the "change of wp") blue,

- Dec 11 (good sensitivity before the baffle installation) orange

- Jan 8 (after baffle installation) purple

It can be noticed that:

- B7 is slightly different (Etalon NI loop actually open)

- B1p DC is back to the October level

- Sidebands lower than October but higher than December

- Higer CMRF (similar to October)

- SRCL set lower than October but higher than December

- DARM OG same as December

- MICH set much lower than december

The working point seems that has been recovered with respect to December (indeed no MICH offset is needed in the lock acquisition)

The Online DetChar tools are enabled and processing data when available. Omicron live, UPV and BruCo with a 1-day latency.

Yesterday (Jan 8) I have run out of time to make a proper realignment of the EDB OMC in LN2. I have just done a 5 minute check that there is no obvious way to make a large improvement in the transmitted power when locked on the 56MHz USB TEM00, and then proceeded with a scan of the EDB OMC with the same parameters as in the past few months: freq 0.002Hz, ampl 0.5, offset 23.27.\

17:59 UTC (40min) EDB OMC scan with standard paratmers

18:40 UTC (20min) EDB OMC scan with the speed reduced by a factor 4 to more easily see on the camera which mode is which peak

Figure 1 shows the scan with the carrier HOM and the 56MHz USB TEM00 highlighted. The alignment of the EDB OMC is not great, as the order 1 mode of the 56MHz has about half the power of the TEM00.

This could be compared to a previous detailed study from July: https://logbook.virgo-gw.eu/virgo/?r=67382, but the EDB B1t photodiode has been changed in the meantime, and I am not sure its calibration is correct anymore, so the absolute power cannot be compared. It is more directly comparable to the measurement from November: https://logbook.virgo-gw.eu/virgo/?r=68097.

Figure 2 superposing the scans from yesterday and from November what is striking is that the power of most of the HOM has doubled, with the exception of modes order 5 and 9. While the power of the 56MHz sideband TEM00 is comparable.

Figure 3 zooms around the order 2 mode. There were almost a factor 2 fluctuations in that power yesterday. 

Figure 4 zooms around the order 3 mode.

Figure 5 zooms around the order 4 mode.

Figure 6 zooms around the order 5 mode, they are indeed the same yesterday and in November.

Figure 7 zooms around the order 6 mode.

Figure 8 zooms around the order 7 mode

Figure 9 zooms around the order 8 mode

Figure 10 zooms around the order 9 mode

Figure 11 zooms around the order 10 mode

The increase in HOM power is also compatible with what is seen on the SDB2 B1s photodiode. Which in November was fluctuating between 20mW and 24mW during the scan, while yesterday it was fluctuating between 20mW and 40mW. So maybe the issue is that interferometer is less stable in LN2 than it used to be. In particular the BS TX loop was in drift control yesterday, maybe it was in high bandwidth during the measurement in November.

Looking at B1p, the power in November was fluctuating between 340mW and 400mW, while yesterday it was fluctuating between 230mW and 280mW. It is very confusing that the change we observe on B1p is in the opposite direction to the change in power we observe on B1s.

Looking at the shapes of the different modes, I have the impression that back in November most modes had a double peak structure, corresponding to a power distributed between the horizontal and vertical direction as the OMC is slightly astigmatic, while in January the modes are more single peaked, which would mean there is a preferred direction of the HOM. On the other hand it could be just a coincidence if the power of the higher order modes is fluctuating due to alignment, and it happens to be that for each resonance we see only one cycle of alignment fluctuations. Locking on each mode individually would allow to check how stable they realy are, and if there is a preferred direction.

ITF found in commissioning mode with the ISC activity of ITF with aligned SR in progress.

Then the ISC team made a SR horizontal translation.

At around 17:50 UTC, with the ITF in LN2, Michal started to work from remote; activity concluded at 19:10 UTC.

In agreement with Diego and Michal the ITF was left in LN2 with the autorelock enabled to relock in LN2.

The SR has been tralated horizontal of about 0.5mm to check effect on the sensitivity and on the WP.

see attached plot

no clear effects are visible

Today after having reached LN3 (56MPc) we have aligned the SR (no offset on tx and ty). The transient is visible in the attached plot.

The sensitivity was quite low and worsened by the high CMRF. We re-engaged the BS ty loop but the required offset was too high to keep the lock.

data to be analyzed to evaluate the level of noise.

to be noted:

DC readout gain tuning (ITF_LOCK.ini)

#371 darm_gain_pd3 from 0.25 to 0.3

#383 darm_gain_b1_dc from 0.4 to 0.35

At 23:40 LT the Injection system was recovered after manually restoring the position of the MC, IB and BPC (also lowering the corrections of the BPC). It seems that the issue started after an oscillation of the EIB control loops. 

ITF found in relocking up to CARM_NULL_1F, in UPGRADING mode.

After several attempts ITF acheived LN3. COMMISSIONING mode set.
After the unlock occurred at 18:28 UTC (from LN3) the SBE_EIB loop started to ring, so the ISYS system got stuck. I contacted the OnCall who tried to fix it. Recovery attempt up to 22:00 UTC. Not concluded. Activity planned for tomorrow morning.
TROUBLESHOOTING mode set.

DAQ
TelescreenLeft, TelescreenRight VPM processes restarted twice.

Today we reached the lock up to LN

We had several unlocks:

- many ALS unlocks

- many CARM2MC (for this reason the gain has been decreased from 1.3 to 1.1)

- two DIFFp ty high frequency oscillation @ CARM 0, gain decreased from 12 to 9

- 2 unlocks at the B1 PD3 handoff (gain decreased from 0.36 to 0.25)

- 1 unlock for B1s too high (threshold increased fro 44 to 48)

In order to lock the OMC we have misaligned the SR ty +2urad at the end of carm0 1f

ITF found in upgrading mode with the NORTH cavity unlocked, WEST cavity locked and  BS-SR valve closed.

At around 7:00 UTC the commissioning team started to work to retreive the alignment of the NORTH cavity; the north cavity was locked around 9:30 UTC.

After that we started to recover the alignment of the CITF (see SR TX recovery); the CITF was recovered around 13:00 UTC.

Recovery towards CARM_NULL_1F in progress...

Vacuum

At around 7:30 UTC the vacuum team opened the BS-SR valve.

Suspensions

• PR vertical corrections recovered by Paolo.
• At around 12:00 UTC the SIB1 suspensions started to oscillate; to fix the problem I opened the vertical and the horizontal accelerometers; situation monitored by experts.

During the stop for the installation of SR diaphragm, SR mirror changed its orientation in TX by about 800 uRad, for the same orientation of the marionette (according to MAR optical lever signal). The alignment of SR cavity was possible only after the recovery of the old value on MIR optical lever.

A reduction of voltage on MAR actuators has been attemped by the use of the motorized MAR balancing. Normally both TX and TZ motors needs to be used for a good zeroing, but TZ motor had some troubles: after a small amount of steps in one direction, the balancing changed discontinuously and it was not possible to revert the change going back with the motor. I decided to stop using that motor and I changed the set point for TZ, from 0 to 1.5 mRad. This is a rotation around the mirror optical axis and the effect on the optical behaviour should be null.

Currently the corrections are not very small (about 3 V), but they can stay like that without any risk.

This morning, I closed the angular control loop of SDB1 at 09h02m31-UTC.

The angular control loop of SDB2 were closed at 09h12m43-UTC and its position loop were closed at 09h14m05-UTC.

In agreement with Antonio, I ve switched off the NI etalon loop

Yesterday a leak became evident in the central area: this morning we progressively isolated  the different vacuum chambers and by RGAs and helium leak detector we finally localized the leak in the external vessel of the NI cryotrap. In attached: a picture of the leaking area and a technical drawing of the concerned part: the defect is located on a lateral finger, likely in the edge-welded bellows or in a weld of the finger pipe itself.

The current leak rate is ~1E-5 mbar·l/s, significant but still manageable. The leak could increase over time.

A temporary fix has been implemented using an external sealing combined with external pumping, keeping the area upstream the leak at a pressure below 1 mbar. The two valves before and after the cryotrap (NI_tower/NI_cryotrap and NI_cryotrap/N_tube) were closed during the works and are still kept closed to verify the correct functionality of the fix  .

Next Wed morning at 8h both valves will be opened and the North arm will become available.

In parallel we prepare for a full replacement with new parts, plan to be discussed with the commissioning team.

ITF in DOWN UPGRADING
7:00 UTC SIB2 position loop closed
9:30 UTC SR Ring Heater switched on (#68440)
10:00 UTC WI AUX laser adjustment: after switching off the laser to replace its chilling circuit water filter (#68435), the laser was switched on, setting waveform generator Pulse Width to 98 us (previously it was 95 us). TCS_WI_CO2_CH_PWRLAS decreased from ~ 375 to ~ 330. Moreso, it took around five days to get to a stable value, which is why we waited to refine the working point. As instructed by Nardecchia, today we gave it a further adjustment by bringing Pulse Width to 115 us, which raised TCS_WI_CO2_CH_PWRLAS to 390. We expect the value to stabilize in the next few days, thus the threshold adjustment is postponed, if even actually needed.

Since tomorrow is a national holiday and given the fact that commissioning will start on Wednesday morning, some maintenance procedures were carried out this morning, including:

• GPL refill
• TCS chillers refill
• Vacuum maintenance: NI large valve is temporarily closed (updates pending), SR_BS large valve still closed and ready to be opened
• Adjustment of TCS CO2 NI/WI PWRIN/OUT thresholds 

TCS usual checks were carried out yesterday by Nardecchia, the maintenance concerning nitrogen will be carried out as usual tomorrow morning by the vacuum group.

After receiving approval from Antonio, the SR RH was powered on at nominal power at around 09.30 UTC [V = 23.13 V I= 0.35 A (P= 7 W)].

Between Wednesday afternoon and Thursday morning, EIB started to oscillate several times, probably due to sismic activity, causing the BPC loop to open suddenly. As a consequence, BPC corrections went away and I had to recover them manually once the bench calmed down. 

Moreover, after the last BPC opening, Narm couldn't relock by itself. PR mirror has been moved transversally to recover the arm lock. Finally I brought back the PR in its last position.  

ITF in DOWN UPGRADING
7:00 UTC to 10:00 UTC SIB2 vertical loop kept opening: vertical position adjusted with motors. 
14:00 UTC Strong wind activity on site, sea activity flag red, Mwp 6.5 earthquake in Mexico, subsequently SIB2 horizontal loop opened. Given the conditions, I left it open.

ITF DOWN in UPGRADING
Activities carried out this morning:

• Check of EER temperature: eurotherm sensor read 19.4 °C, ENV_EER_TE 16.8 °C. Room conditions were fine, ENV experts were notified (Andreazzoli, Tringali)
• TCS chillers water levels check (Ciardelli)
• SR RH was switched on and switched back off (68434 Nardecchia)
• TCS Aux Lasers cooling tank filter maintenance (68435 Ciardelli, Zaza, Nardecchia)
• SR tower pumping in progress (Vacuum team)

At around 13:30 UTC, INJ unlocked and EIB started oscillating. No seismic activity. I contacted INJ experts, relock in progress (Spinicelli).

After noticing a negative drift in TCS_AuxCooling_NI_FLOW (picture 1) we turned off both WI and NI aux lasers and proceeded to extract and regenerate the filter, whose condition before and after can be seen in picture 2 and picture 3. Water flows were restored, NI aux laser PWRLAS went back to its working point, WI PWRLAS recovery is still ongoing.

The RH was switched off after Antonio reported that the pressure was 20 mbar; RH operation is not allowed before 4 January. 

At 08:51 UTC, the SR RH was switched on at the usual power (V = 23.13 V, I = 0.34 A).