The activity regarding the balancing of NI, WI and SR MAR Z actuation is concluded, because there is no margin to reduce more the coupling from Z CORR ot TY CORR by a simple adjusting of driving coefficients.

The impact of the re-balancing on the alignment stability has been evaluated, comparing recent data in moderaterly windy condition with older data in similar condition (fig 1). The spectrum of the alignment error signals correlated to the Z actuation mis-balancing is shown in the following figures. DIFFp_TY, the most important d.o.f. of the arm alignment, is shown in fig 2: there is a clear improvement below 0.1 Hz (the changes above 0.1 Hz are very likely independent on the actuation balancing). In order to understand whether the improvement is big or small in terms if ITF stability, the total rms is the quantity more appropriate to look at. In fig 3, a calibrated version of DIFFp_TY is shown, including the cumulative rms. The data refers to the first time slot, before the optimization of the balancing. We can see that the largest contribution to the alignment fluctuation comes from the frequency band above 0.1 Hz; the margin of rms reduction is about 10 %, in this environmental condition. Following this criterion, the expected improvement of the ITF alignment quality, induced by the actuation re-balancing, is small.

North arm and west arm TY SOFT d.o.f.s are shown in fig 4 and fig 5. Both are more accurate after the balancing; especially north arm. We can guess the total rms to be significantly improved as well, but this analysis is not straightforward, when the in-loop error signals are optical levers. Moreover, we use to consider the ITF quite tolerant respect to SOFT fluctuation and we never had the impression to be close to some limit, concerning the accuracy of those d.o.f.s. In conclusion, it is difficult to assign a grade to the obtained improvement.

Fig 6 shows DIFFp_TY, the last d.o.f. on which NI WI actuation balancing should have an impact. In this case no improvement is visible: the recent data are even worse. This is something to better investigate: a different noise source needs to be identified, which overcome the effect of the actuation mis-balancing.

Fig 7 shows SR_TY: the rebalancing has an effect, likely not relevant, as already discussed in a previous entry.

Finally, let's try to find the effect of the actuation balancing on the usual overall figures of merits: B1p power (fig 8 ) and sidebands power (fig 9). According the choosen data, there is no visible improvement.

This morning we compared B1p_QD1_50MHz and QD2. An offset was introduced on the QD1 signal until the other was centered in 0.

There are a couple of interesting effects:

• the coupling of RIN with DARM (LSC_DARM_PSTAB2_COUPLING) improved noticeably
• the high-frequency coupling between SSFS and DARM (DARM_SSFS_LINE) worsened noticeably

ITF found in Science mode.

ITF unlocked at 8:14 UTC because of the following earthquake: M 6.0 - 120 km E of Yamada, Japan; ITF back in Science mode at 9:27 UTC.

From 10:01 to 10:02 UTC ITF in Commissioning mode to test the BS_TX offset to zero the QD2 signal instead of QD1.

Suspensions

OB F0 coil H2 close to saturation (see plot); experts informed by mail.

SBE

SNEB F0 H2 actuator drive close to saturation (see plot); experts informed by mail

Friday, November 7, 2025 at 10:48 PM xenhost146.virgo.infn.it crashed and these machines have been rebooted on another host:

• w3.virgo.infn.it (https://scientists.virgo-gw.eu)
• pub26.virgo.infn.it (TDS, Logbook and DRS)
• pub22.virgo.infn.it (https://apps.virgo-gw.eu)
• datagw2.virgo.infn.it (data transfer machine)
• mysql1.ego-gw.it (Mysql server for TDS, logbook, drs)

All services have been restart correctly except for w3.virgo.infn.it (https://scientists.virgo-gw.eu) where we have reported some issue on mounting points side. What I did by terminal on my smartphone it turned out not to be sufficient to fix the issue reported us by email by Nicolas Arnaud.

Only today I found out a possible culprit and fixed the configuration to avoid the same behaviour on reboot.

Figure 1. The WI etalon correction has started to drop to zero several hours per day without a good reason. This should be investigated.

It is also important to add DMS flags to monitor the Etalon loop more precisely, and spot these type of issues more easily. For example a flag turning yellow whenever the correction is zero or saturating.

ITF found locked at LN3 in SCIENCE mode. 
It remained locked for the whole shift.

6:00 UTC ITF found in SCIENCE
8:27 UTC unlock, IPs flags red, SWEB loop open, SEISMON and SEA_ACTIVITY red
8:46 UTC EARTHQUAKE MODE, ITF kept in LOCKED_ARMS_IR, as far as possible
10:44 UTC ITF in PREPARE_SCIENCE: arms and central alignment were almost not needed, I tried to add an offset to MICH (+60) but while B1p_DC went from 0.03 to 0.026 the 56MHz sidebands (not superposed) diverged. I brought the offset back to 20 and not only did the sidebands converge but B1p actually lowered to a value that was inferior to the one it had when the same offset was added ramping up.
11:50 UTC ITF in SCIENCE, left in SCIENCE

Guard Tours (UTC)
6:30 - 7:10
9:00 - 9:40
12:00 - 12:40

8:12 UTC plane transit

ITF found in LOW_NOISE_3 and in Science Mode. It kept the lock for the whole shift.
ITF left Locked.

No DMS alarms were received during the shift.

DAQ
At 00:58 UTC, the DMS reported grey signals related to the Suspension. The processes SUSP_Fb and FbmFFE both reported issues at the same time.

ITF found in SCIENCE Mode and LOW_NOISE_3 State.
All times are UTC.
19:30:01 CALIBRATION Mode set:
Calibrations started after ~35 minutes of BNS drop (from 18:34 to 19:10) and after the ~25 minutes glitch happened at 19:26;
From 19:30:30 to 19:42:44 Check hrec (CALIBRATED_DF_DAILY);
From 19:44:00 to 19:02:00 ISC injections (inject_asc_test.py), noted ~30 minutes glitch during injections at 19:56;
20:02:49 SCIENCE Mode set back;
ITF kept the lock for the shift;

Guard tours:
14:38 -> 15:11
17:01 -> 17:31
20:19 -> 20:56

ITF found locked in LOW_NOISE_3 with SCIENCE mode (Autoscience OFF); BNS Range ~53 Mpc.
07:15UTC - ITF unlocked due to BS_TX glitch(? pdf 1) with IP loops yellow on DMS due to wind and seismic activity. After recovering arm cavities and CITF alignment (NI_TY+=1 urad, SR_TY-=4 urad) ITF relocked at first attempt without MICH_SET ramp. LN3 achieved at 08:42UTC, in SCIENCE mode at 08:45UTC.
11:05UTC - ITF unlocked due to same but faster glitch(? pdf 2). Relocked to LN3 (with MICH_SET=40) at 11:56UTC, back in SCIENCE at 11:59UTC.

Guard tour (UTC)
05:57 -> 06:40
11:30  -> 12:02

ISC
08:42-09:40UTC - ViolinModes briefly excited after relock (DMS in fig.1). BNS range unstable, oscillating between 36-54Mpc

Figure 1. The main laser amplifier temperature has been slowly increasing over the year and it is now close to the highest it has been back in November/December last year before the Neovan cooling circuit improvements. 

At that time we had issue with glitches below 100Hz appearing and disappearing, and the BNS range being lower: VIR-1047A-24. Thes problems disappeared more or less at the same time as the Neovan cooling was improved, but there has been no clear proof that one is related to the other.

Figure 2 and 3 shows that currently we have a similar looking problem with decreases in the BNS range and glitches below 100Hz. 

It is important to improve the Neovan cooling at the next maintenance. Mainly because the temperature is too high, but also because there is a chance it will solve the issue with the BNS range drops and associated glitches.

It can also be interesting for someone to look at other PSL channels during the periods of elevated noise in the past few days. Is there more noise or glitches on the power stabilization loop, on the PMC length loop, ... ?

ITF found in LOW_NOISE_3 and in Science Mode. From 14:17 UTC to 14:21 UTC Bersanetti set the ITF in Adjusting Mode to restore the BS_TX back in full bandwidth (see report #68117).
ITF left locked.

Guard Tour (UTC)
21:56 - 

Figure 1. Looking between 1Hz and 9Hz at the various dither lines in B1p QD1 and QD2 50MHz V I,  in the vertical direction there is large difference in coupling from other degree of freedom. The DIFFp TX line (3.3Hz) and SR TX line (5.1Hz) is 3 times higher in QD2 than in QD1, but the SDB1 TX line (4.3Hz) is 10 times lower. So B1p QD2 maybe a much better or a much worse choice in terms of angular control cross coupling, depending on which couplings (if any) are creating issues.

In terms of signal the amplitude at low frequency (below 100mHz) of the QD2 signal is 10% higher than for QD1, and the sign is the same.

Today around 14:15 UTC I have increased the flag threshold for the the Z -> TY MAR coupling for NI, WI and SR by an order of magnitude from 1e-4 to 1e-3. So that the flag is not red most of the time. Based on the fact that without intentional injections we are not able to measure the coupling for those mirrors as precicely as for PR: https://logbook.virgo-gw.eu/virgo/?r=68109

This afternoon just after the daily meeting (14:18:15 UTC, ramp = 5 s) I enabled BS_TX in full bandwidth.

Profiting of no detector Observing, I also re-instated it in the lock acquisition, line 6183 of ITF_LOCK.py. In case again of unlocks in ACQUIRE_LOW_NOISE_3, that line should be commented back and the node reloaded.

I looked at the data from yesterday:

• also in the second test, the handoff of BS_TY from QD1 to QD2 improved several signals, especially the ones related to sidebands; the effect on the range was, again, not as good;
• the two QPD signals have different offsets, as the handoff changed the behaviour of the setpoint servo of the loop itself;
• this also caused a change in behaviour of the SRCL setpoint servo, which showed a jump downwards; the MICH one, instead, did not show any particular change.

In Figure 1 a snapshot around the time of the changes, in Figure 2 a much longer trend of the night.

The change of the BS_TY sensor has been automated, only from CARM_NULL_1F onwards; the configuration for the loop while still on the DRMI has been left on QD1.

ITF found locked at LN3 in SCIENCE mode. It remained stable locked for the whole shift.

10:33 UTC (one minute) - ADJUSTING mode for NI balancing (Pinto).
13:28 UTC (one minute) - ADJUSTING mode for re-Load ITF_LOCK (Bersanetti).

The transfer function from MAR Z CORR to MAR TY CORR for SR is shown in fig 1, before and after the adjustment, in similar condition concerning the wind speed (between 20 and 30 km/h). The adjustment is effective between 10 and 40 mHz, but it goes in the opposite direction at higher frequency. Given that the aim of the action is to reduce the angular fluctuation of the payload, it is useful to look at the error signal, shown in fig 2. One can see an improvement below 40 mHz and a smaller worsening in a bump between 50 and 80 mHz. I would interpret it as a general improvement of the situation, but it remains to explain why the balancing is not effective in the same way at all the frequencies.

The other big difference visible in the error signal, above 0.1 Hz, is not an effect of the different actuation balancing; this is not even a real angular motion, because it is something happening at the level of the sensing. The optical lever that measures the 'horizontal' rotation has a natural coupling with the horizontal translation of the ground. This is normally minimized by the optical setup, putting the PSD perfectly in the focal plane of a lens. The bumps at 0.4 Hz visible in the data are the microseismic peak and are different because the sea activity is different in the two cases. The sensing coupling seems a bit too high, with respect to the performance we normally can obtain. It is not directly a real angular motion, but it produces a lower accuracy of the angular control, because the control reinjects partially the sensing noise as a real rotation (not totally, because the gain of the loop is lower tha 1 at that frequency).

The sensing coupling of the seismic noise on the angular sensor can be a possible explanation of the strange effect discussed above, concernig the effect of the balancing at low frequency. This coupling adds a component in the transfer function from MAR Z CORR to MAR TY CORR, which remains different from zero when the balancing is perfect and produces a bias in the determination of the good balancing. In this case, the balancing can be verified by a direct noise injection in MAR Z CORR, instead of taking data when the locking force is applied.

Coming back to the current performance of SR TY control, I would say that the residual imperfections on the sensing and eventually on the driving are small, with respect to a reasonable requirement. We are talking about a small fraction of urad, while we know that the ITF is tolerant to a few urad of SR misalignment.

The accuracy of the MAR Z actuation balancing can be better measured when the wind is strong (we are waiting for data in that condition), but it is interesting to observe tha data also in quiet condition. The adjustment performed yesterday on WI balancing is visible in the attached plot, but we can see that the improvement is no more visible below 50 mHz because the measurement is too noisy. The same measurement performed on PR is much cleaner, thanks to the cleanliness of the reference signal - tyCorr. The noise on that signal comes from the in-loop angular error signal, which is quite sensible for PR. For the arms, the error signal is a combination of different sensors, one very good (DIFFp), the others not very sensible at low frequency. For this reason, the on-line monitoring of the balancing can be very accurate only on PR. A low threshold used also for the the other DOFs leads the flag to be red too often.

All times are UTC
ITF Found DOWN State and in PREPARE_SCIENCE Mode 
Ruggi and Pinto are working on balancing of NI and SR Marionettes (ended at 15:08, see #68109);
During the relock the ITF strugled a bit during the alignment of the CITF, I set MICH offset to 40 with 4 steps of 10 in 60 s each;

At 15:31 CALIBRATION Mode set during the relock:
ITF in LOW_NOISE_3 at 17:10;
From 17:12 to 17:31 CALIBRATED_DF_SENSITIVITY;
From 17:33 to 17:52 CALIBRATED_DF_PCAL;
From 17:53 to 18:09 ISC Injections (inject_lsc.py);
At 18:09 COMMISSIONING Mode set under request of Bersanetti for BS TY Loop tests (see #68100);
At 18:30 SCIENCE Mode set.
ADJUSTING Mode for BS TY Loop tests:
From 18:40:16 to 18:41:45;
From 19:04:01 to 19:05:28;

Guard tours: 
19:16-19:48

The test with the QD2 sgnal lasted up to the unlock. I then disabled it by hand as the automation did not know about it, then I added in DRMI_LOCK the reset of this new sensing matrix weight.

At the end of the calibration activity there is clean data from 18:11 UTC for 300 s; then, after a 25-minutes glitch, I changed the BS_TY loop sensor again from QD1 to QD2 at 18:20:03 UTC; clean data afterwards for 20 minutes.

At 18:41:12 UTC (ramptime = 5 s, in ADJUSTING mode) I opened the SR_TY loop, clean (SCIENCE) data for another 20 minutes. I enabled the loop back at 19:04:11 UTC (ramptime= 5 s).

This afternoon, profiting of an unlock of the ITF, we worked on the actuation balancing on SR, WI and NI payloads. We modified the DSP cards implementing few lines of code in order to change the coefficients of the driving matrix, by sending directly a fraction of the longitudinal correction (Z) to the angular branch (TY). The coefficient to be implemented is directly evaluated and updated by adding the measured value of the transfer function at low frequency between MAR_TY_CORR and MAR_Z_CORR.

In the next long locks the effect on the new balancing coefficients on the general alignment performance of the ITF will be evaluated, wrt to the previous conditions.

By looking at the data we will try to understand the possible tresholds values for the DMS flags monitoring the couplings.

ITF found in LOW_NOISE_3 and in Science Mode. From 11:09 UTC to 11:21 UTC, Bersanetti set the ITF in Adjusting to perform a manual handoff (see report #68106);
The ITF unlocked at 13:32 UTC, taking advantage of the event Ruggi and Pinto started performing the balancing of NI and SR Marionettes.
Activity in progress, ITF left unlocked.