Motivation for the shift

During this shift, several arm scans are made in order to characterize the optical properties of the North and West cavity. The scan will be used in order to:

-> Measure the astigmatism amplitude. From previous measurement (66835), the astigmatism amplitude appeared to be smaller in the North arm when the ring heater is turned off. No measurement has been made for the West arm since the RH were turned off during the change of the WE mirror. The data from this shift will be used to redo the measurement in both arms.

-> Discrepancy between the characterization made at LMA and from scan (VIR-0562A-25). According to previous measurement, there is a discrepancy between the expected g-factor and what is measured from the scan. The estimation will be done again and for both arms.

-> Most of the scans are made with a misalignment of the end mirrors in order to measure the orientation of astigmatism.

Shift report

Date of the shift : 15th December 2025

The table below shows the tasks performed and their time in UTC. The scans are run with the command CARM_SET_scan_FSR(numiteration = 10, f_FSR=110000,timescan = 60.), where one iteration corresponds to one descending ramp + one ascending ramp. One iteration produces two scans, each one is 60 seconds long.

ITF found in upgrading; see entries 68378 , 68374 , 68379

At the beginning of the shift the Arms FSR scan activity could not be performed bacause the arms valves were closed.

At 8:27 UTC Antonio opened the arms valves; no flashes present in the arms. I was able to find the flashes by looking at the NI,WI,BS mirror positions and finally the cavities were locked at 9:20 UTC.

At around 9:00 UTC Ettore entered in the SR tower, see Weight checks meant to stray light baffle substitution.

At around 10:30 UTC Jacquet started to perform the Arms FSR scan without RH; activity still in progress.

Software

At 8:08 UTC BacnetServer restarted because it was providing flat signals.

SBE

At 8:16 UTC I closed the SNEB position loop; SNEB loop closed again at 9:30 UTC and vertical position recovered with stepper motors.

Venting of SR tower is in progress

• 12h30LT BS/SR and DT/SR valves closed and SR tower isolated;
• 13h15LT venting started;
• arms valved off

Note: G21 / SR link to be replaced during the shutdown

ITF found relocking in COMMISSIONING mode.
At ~17:30 UTC D. Lumaca switched OFF NE, WE and SR RH.

At 17:58 UTC, under request of Gouaty, I performed the following actions:
- SDB2_LC: Open Angular Loop
- SDB2_SBE: Open Position Loop
- SDB1_LC : Open Angular Loop 

At 18:09 UTC, according with the planning of SR intervention, I opened SR loops: LC, F7, ID.

ITF left in LOCKED_ARMS_IR arms. Manually locked via ARMS_LOCK; although ITF state appears DOWN on ITF Event Monitor and DMS.
DET_MAIN, DRMI_LOCK, ITF_LOCK in PAUSE, in UPGRADING mode.

In view of the opening of the SR tower, I setup the automation in the following way:

• DET_MAIN in SHUTTER_CLOSED, then paused;
• SUS_SR in MISALIGNED, then paused;
• DRMI_LOCK in MISALIGNED_PR_SR, then paused;
• ITF_LOCK in DOWN, then paused;
• SUS_PR in MISALIGNED, then manual;
• OMC_LOCK in TEMP_CONTROLLED, then manual;
• INJ_MAIN in IMC_RESTORED, then manual;
• ARMS_LOCK in LOCKED_ARMS_IR, then manual;
• all other nodes unchanged.

As a consequence, the DMS and in general the webpages will not reflect the status of the interferometer anymore, as it is desumed from the state of ITF_LOCK.

For the following weeks, the nodes INJ_MAIN and ARMS_LOCK should be (almost) the only ones to be operated manually; they will not talk with one another, so people should take care of both:

• INJ_MAIN: unless the FmodErr tuning is really needed, IMC_RESTORED is the target state

• ARMS_LOCK: nothing above LOCKED_BEATING_BOOST_ON should be requested

The SR RH have been switched OFF at  17.31 UTC, in preparation for SR venting foreseen for tomorrow.

As a second step, the ETM RHs have been switched OFF for the measurement of arms astigmatism.

17.29 UTC NE RH OFF

17.30 UTC WE RH OFF

We had a look at tonight injections and compared them with those of the previous night

The examined periods are:

17000 s starting from Dec 11, 01:00 

17000 s starting from Dec 11, 22:20 

We used a spectra resolution of 2000s.

The first dataset is polluted by a 0.1 Hz spaced  comb, which is present in the Voltage and current monitors of the large coil amplifier as well as in the witness magnetometer (placed close to the WE tower).  We suspect this might be related to the injected lines being multiples of 0.1 Hz.  The problem with this is that Hrec itself is polluted by a 0.1 Hz comb, although it is not related with our injected noise. Infact, as shown in Figure 16 (example around the injected line 10.5Hz) the same 0.1 Hz comb was present also when not injecting (purple). 

Therefore, in the second set of injections we moved the lins frequencies at **.*77 Hz. This time we noticed a somehow larger spectral noise "floor" in the Voltage, Current monitors and magnetometers as well, which resembles a comb spaced by 0.77 Hz. However, this turns out to be better, because no such comb is present in Hrec a priori.

Going through the injected lines one by one (Figures 1 to 15), it looks that we have achieved a good measurement of CF at most of them. Missing ones for now are 3.6, 4.6, 5.7 Hz, which might be recovered improving the analysis.

We do not have a good explanation for the extra noise  produced by the amplifier, it seems related to a non linearity in the amplifier itself, since the spectrum of the injected noise (ENV_NOISE_MAG_WEB) does not show this features.

As agreed with Michal, I reduced the ETM RHs power by 50%, to allow arms astigmatism measurement.

13.06 UTC NE RH reduction to V = 11.7 V  (3.7 W)

13.07 UTC WE RH reduction to V = 12.3 V (4.07 W)

In 2024, Antonella Bianchi did also the power decomposition at the dark fringe for various input powers. The results are summarized in the wiki page:
https://wiki.virgo-gw.eu/Commissioning/OptChar/O4_param

In the section " TABLE FOR WHEN THE IFO IS 1h after CARM NULL STATE IS REACHED", the results are comparable to what Michal reported for the dark fringe (not identical but in the same range for most).

This morning we installed the Optris thermocamera on the HR face of the NI mirror, using the same support used for the infrared NI_cam (see Figs. 1, 2 and 3). We adjusted the image focus and connected it to the online streaming, accessible only via EGO Wifi, at the address : http://172.31.10.103:8080/

On Fig. 4 we can see the images of the thermocamera with the ITF locked. The last attachment is a video where we can see the appearance of the PAs while the lock acquisition takes place.

The phase camera data for an aligned phase camera confirms that most of the power on B1p in LN2 is due to the carrier.

Figure 1 shows data from phase camera power of sidebands and carrier and the total of all curves shown. Highlighted is time in single bounce when almost all the power is in the carrier light and in LN2 where most of the power (~80%) is in carrier light. Which is compatiable with the OMC scan measurements that 10% of the power is in the 56MHz TEM00 modes, with a few more percent in sideband higher order modes.

Figure 2 shows the ratio between the PC carrier and total, making it clearer that it is 80% of the power.

In April/May 2025 the EDB OMC was installed, this has misaligned the phase camera as reported previously. It was realigned during that break, but the alignment drifted away again over a month following the break.

Figure 3 shows data in July 2025, with the PC misaligned, and the interferometer in LN2 around 18:00 UTC. Note that the vertical scale is the same as in figure 1, highlighting there is 5 times less power on the phase camera than there used to be. 

Figure 4 zooms the horizontal axis, about 65% of the power detected by the phase camera is in the carrier light in LN2. However, given that the phase camera is strongly misaligned this data may be misleading, as most of the light is likely actually not reaching the phase camera.

Figure 5. Coming back to the 2024 data that should be reliable, the power on B1p in LN2 is ~275mW. With 80% of carrier light that corresponds to 220mW. The contrast defect of CD = 2 * B1p / P_PRC = 2*220e-3/17/39 = 660ppm. In LN3 the power on B1p is 150mW, with 60% of it in carrier light, so 90mW of carrier light, and a contrast defect of 2*90e-3/17/39 = 270ppm, which is within the error bars of the 286+/-24ppm reported in the O4 optical characterization paper (VIR-0710B-24).

/users/mwas/PC/PC_contrast_20251211/longTermTrend.m

The NEB and WEB PCal fast server configurations have been updated to allow to use or PD1_DC or PD2_DC to allow the PCAL lines injections.

Operations performed at 2025-12-12-04h03m51-UTC

After these operations, the PCAL loops were succesfully closed with the PCAL lines injected 

• PCAL_NEB: using Tx_PD2_DC instead Tx_PD1_DC as the power on Tx_PD1 is lower than usual 
• PCAL_WEB: using Tx_PD1_DC as usual . By mistake Tx_PD2_DC was set, restored to Tx_PD1_DC at 2025-12-12-09h52m08-UTC 

The WEB magnetic line injections were stopped this morning at 08:29:12 UTC.

Due to the comb lines spaced by 0.1 Hz, we changed the frequencies of all injected lines and increased the amplitude of the first four lines in order to improve their SNR.

*** The injection started at 21:02:51 UTC in the WE building, and it will be stopped manually tomorrow morning****

ITF found in Commissioning mode and in LN2;  activity of SDB1 angular injections in progress.

At around 14:30 UTC started the planned activity of  Removing B5 beam from SDB1 control and automating it ; actvity concluded at 20:10 UTC.

Then, with the ITF locked in LN3, Maria and Irene from remote started to inject magnetic lines; the injections will remain active for the night.

The ITF has been left in relocking phase (lock of the OMC) and in Commissioning mode (state requested for the ENV injections); in agreement with Diego tha autorelock has not been enabled.

After 2 hours the interferometer has unlocked with an accelarating drift in MICH offset and BS TY INPUT. It is likely related to the changes made earlier this afternoon. I have tried to comment out all of the changes and go back to the previous (standard) control for SDB1.

When trying to move the B1p QD1 112MHz centering actuator from the
quadrant galvo to the SDB1 bench after a minute or two the BS
alignment start diverging. I don't understand why. It doesn't seem to
have been a problem during the test in July:
https://logbook.virgo-gw.eu/virgo/?r=67410

Either the problem is new, I don't remember a change needed to make it
work in July, or it wasn't a problem because I did not stay long
enough in DRMI and moved on with the lock acquisition where the BS
drift control is disabled. The last explanation is the most likely as
doing the swap just before leaving DRMI 3F worked and the lock
acquistion continued to CARM NULL 1F.

But before arriving that I have made many trials, and ended up
increasing the H gain of B1p 112MHz for SDB1 control by a factor 4,
and the V gain by a factor 6.

Changing B1p QD1 alignment with picomotors so zero of 112MHz error signal
matches good alignment of SDB1 in CARM NULL 1F.

B1p_M2_H -400 steps
B1p_M2_V +700 steps

After that the lock acquisition could continue to LN3 without problems
(with the usual SR TY +2 urad before locking the OMC).

Once in LN2 there is the issue that DARM drift control moves the beam
away from the center of B1p QD1. As the low frequency control becomes
the OMC alignment, and no longer the B1p 112MHz quadrant signal. Some
solution may be needed for that if it proves to be a problem. For
example turn on the B1p galvo with very low gain to remove that
offset.

Commented out the enable of SDB1 drift control in
LOCKED_DRMI_3F_ASC_FULL of DRMI_LOCK

Put it instead in SETTING_CARM_OFFSET_MID of ITF_LOCK along with
disabling the B1p QD1 galvo

17:46 UTC Unlocked on purpose and reloaded DRMI_LOCK and ITF_LOCK to
see if automating this procedure works.

Relock to CARM NULL 1F was successful at first attempt

Added to automation offsets into the B1p QD1 galvo correction, as a
simple correction to keep the quadrant centered when the OMC drift
control is enabled. In the future it will need to be replaced by some
slow loop to keep the quadrant centered.

Unlocked when trying to stop the automation to correct a type before
reaching LOW NOISE 2.

Unlocked when trying to adjust the galvo correction offset in LN2 too
fast, as the OMC drift control was not compensating for it.

Put a value of 2.5 in horizontal in the automation and increased ramp
time to 300 seconds. Also added a reset to zero in the DOWN state, but
haven't checked that it works. Probably a larger offset is actually
needed to have the quadrant centered, and some offset on the vertical
direction too.

Note that after DRMI 3F it is now normal that the B1p QD1 galvo loop
is open. I have adjusted the DMS flag accordingly
 

The investigation of the 401 Hz peak was carried out at the turbo pump of the INJ tower. It is worth reminding that, unlike the DET tower, there is no bellow between the turbo pump and the INJ tower.

We injected magnetic and seismic lines at 390, 395, 401, 405, and 410 Hz.

The amplitudes of the injected seismic and magnetic lines were tuned to match the amplitude of the 401 Hz line observed in the accelerometer (ENV_IB_ACC*) and magnetometer (ENV_IB_MAG*).

From a preliminary look, we noticed:

• Seismic line injections: the lines at 390 Hz (ampl = 0.2), 395 Hz (ampl = 0.4), and 410 Hz (ampl = 1.6) arose in Hrec.

• Magnetic line injections: for the coil axis along the North arm and vertical directions, the line at 405 Hz (ampl = 0.8) arose in the sensitivity.

• Figure 1: during the seismic injections, some lines also became visible in the magnetometer, probably because the oscillation of the tower generates a modulation of the Earth-field lines.

The details of the actions performed are reported in the attached files.

This afternoon, we continued the activity initiated last monday (https://logbook.virgo-gw.eu/virgo/?r=68327) to measure the coupling of angular noise injections on the SDB1 bench marionetta, given different conditions of SDB1 alignment.

ITF locked in Low Noise 2 at 12h57 utc.

Taking reference data from 12h58m00 utc (7 min).

2.1/ SDB1 bench aligned

Injection in TY:

Injecting noise with ampl = 4e-5, pole at 40 Hz, corresponding to 8e-2V/sqrt(Hz) above 40 Hz on SDB1_MAR_TY_corr at 13h05m28 UTC (4 min). FIG.1

We notice that even after switching off the noise, there is still a resonance around 90 Hz which is excited. See FIG.2.

We also notice a change in the noise floor above 1 kHz and around 40 Hz.

Therefore we take another reference from 13h14 to 13h18.

Injection in TX:

Injecting noise with ampl = 5e-7, pole at 80 Hz, corresponding to 3.5e-3V/sqrt(Hz) above 80 Hz on SDB1_MAR_TX_corr at 13h18m04 UTC (4 min) FIG.3.

2.2/ SDB1 bench misaligned inTY

Reference position of the bench in TY is : 69.5 urad

TY loop gain set to 0 at 13h25m10

Add an offset of 3 urad in TY at 13h27m33 with a ramp of 60 s.  After observing large fluctuations of the optical gain, we decided to reduce the offset to 2 urad (13h33m00). The bench TY is now around 67 urad.

Taking reference sensitivity data with bench misaligned from 13h33

Injecting noise with ampl = 2e-5, pole at 40 Hz, corresponding to 4e-2V/sqrt(Hz) above 40 Hz on SDB1_MAR_TY_corr at 13h39m21 UTC (4 min). FIG.4

We increased the offset to 2.5 urad at 13h46m03

We increase the offset to 3.0 urad at 13h48m38 with ramp of 20 s. The bench is around TY = 65.5 urad (4 urad of misalignment). Collecting data for 5 min. FIG.5

Offset increased to 4.0 urad with ramp of 40 s at 13h55m08 utc. The bench is around TY = 63.5 urad (6 urad of misalignment). Collecting data for 4 min. FIG.6

We remove the offset from 14h01m13 with a ramp of 120s. The bench reaches the position TY = 70 urad. Collecting data for reference from 14h03m13 to 14h07m13.

We put a negative offset of -3 urad starting from 14h09m41 with a ramp of 120s. The bench reaches the position TY=73.5 urad. Collecting data for 4 min (FIG.7)

We increase the negative offset to -4urad from 14h17m22 with a ramp of 40s. The bench reaches the position TY= 74.5 urad. Collecting data for 4 min (FIG.8)

We switch off the TY noise at 14h22m08 utc and collect again data for 4 min (FIG.9).

We remove the alignment offset from 14h29m22 utc with a ramp of 120s.

We re-enable the TY loop gain at 14h33m51 utc.

Collecting data with bench aligned and no noise from 14h34 utc (4 min).

2.3/ SDB1 bench misaligned in TX (unsuccessful)

We switch-off the TX loop gain at 14h38m05 utc. The bench is aligned around TX = 87 urad.

We misaligned TX by 2urad from 14h40m25 (with ramp of 60 s) but the ITF unlocked due to a too large misalignment of the bench (which actually moved by around 9 urad).

We stopped this activity here.

ITF found locked at LN3 in COMMISSIONING mode.
Magnetic line injections concluded at 06:18 UTC. 07:02 UTC, DQSTUDIES mode set.
ITF unlocked (TBC) at 07:25 UTC and auto-relocked at LN3 at first attempt just in time for the planned activity on WE WiFi Test (Ballester) started at 08:11 UTC. Upon concluded (08:50 UTC) ITF unlocked (TBC).
ITF relocked at LN3 for the planned INJ mag and seis injections. Started at 10:00 UTC.
At 13:00 UTC, upon reached LN2, Gouaty started the planned activity on SDB1 angular injections. Still in progress...

DET
07:11 UTC - B1p_QD1 galvo loop found open. Properly closed via VPM.