TCS

- 19:10UTC: PR CHRoCC VDAC 4.19 --> 0.0 (3600 sec ramp time).

Some remarks related to this event 2025-11-25-13h36m42-UTC 

• there is none log messages reported by the ISC_Fb server receiving the 59 Sc_BS's channels
• all Sc_BS's channels are missing during 40.2ms (see the attached plots)

The file Sc_BS-1448113020-20251125-13h36m42-UTC.txt shows the content of one of the channels 

• the first sample set to zero is the sample id 1517 
• the last sample set to zeor is the sample id 1918

According the TolmFrameBuilder code,  if there is none log messages reported its means that all data were received.

As result, we think that all the Tolm packets from Sc_BS were received and some of them were sent with 0 for all channels by the Sc_BS DSP 

The rotor parameters of NWN and NEN have been swapped and the NEB_NCal configuration reloaded at 17:27 UTC, following the rotors swap of last week. The NWN control parameters have readjusted at 19:09, since they seems to be more related to the controler, than the rotor itslef.

This shift was focused on understanding the differences in HWS-DET illumination observed when the ITF goes from a locked to an unlocked state using a gentle unlock procedure. In this unlock configuration, all mirrors are misaligned except for the NI, BS, and SR (see entry 68056).

This state corresponds to the NI single bounce configuration with SR aligned. So, we started by performing the following measurements:

1. Lock ITF in NI SINGLE BOUNCE + SR aligned

Folder name: 20251125T1455_NI_Single_Bounce

2. Lock ITF in SINGLE BOUNCE + SR aligned + NE aligned

Folder name: 20251125T1501_NI_Single_Bounce_NE_aligned

The CCD illumination patterns acquired in the two configurations, as well as their difference, are shown in Figure 1. From the difference map, it is clear that the NE contributes to the changes observed in the HWS-DET illumination.

Then, two independent sets of measurements were performed, scanning the TX and TY of the NE mirror one at a time.

The reference position for the NE mirror is: TX = –113 µrad, TY = 38 µrad.

The CCD illumination patterns acquired at each step, as well as their differences with respect to the aligned configuration, are shown in Figure 2- 3 for the TY scan and in Figure 3-4 for the TX scan.

After the measurement, we decided to attempt the absorption measurement by performing a gentle unlock, this time without misaligning the NE mirror.  Diego implemented this procedure in the automation.

After the ITF was locked in CARM NULL 1f, Diego noticed that in all previous measurements, the SR position had been mistakenly parked at the misaligned position used for LN3, meaning it was misaligned by –2.3 µrad in TY.

I performed an acquisition in the SR-aligned configuration (ITF in carm null 1F) and compared it with the one acquired with the ITF in SINGLE BOUNCE + NE aligned (see fig.6).

To remain consistent with all the measurement sets performed during the shift, I asked Diego to misalign the SR again by –2.3 µrad in TY. Again, I performed an acquisition in the SR-misaligned configuration and compared it with the one acquired with the ITF in NI SINGLE BOUNCE + NE aligned (see fig.7). 

With the ITF in CARM NULL for 1 hour and 2 minutes (and SR misaligned by -2.3 urad in TY), we started the HWS-DET acquisition at 18:22 UTC ( 20251125T1922). 

At 18:27 UTC, the ITF was manually unlocked (WF 9) using this special gentle unlock configuration, in which the NE remained aligned.

One of the wavefront acquired after the unlock is shown in figure 8.

The structure observed in the measurements described in entries 68058 or in 68051 is no longer visible. It was caused by the HWS beam reflected by the NE, which disappears after the unlock. The final check would be to repeat the measurement with the SR aligned.
At 19 UTC, I interrupted the measurement.

The following maintenance was carried out between Tue Nov. 18th and 25th:
CEB main service water: replacement of all 6 water filters
Clean Lab ultra pure water system: replacement of 2 ultra pure water pre-filters, replacement of Millipore Q-guard elix 70 filters, replacement of Millipore UV Lamp

This morning the "keep sample" function has been activated on the Master board of Sa_BS.
It seems that the glitches (which are actually transmission bugs rather than real glitches) have been significantly reduced.
We will continue monitoring the signals.

here is the longitudinal noise budget of the last set of injections performed on saturday 22nd. Projections made wrt Hrec.

here is the angular noise budget of the measurements performed on saturday 22nd. No major differences in terms of coupling with respect to the previous set of injections. Dp ty still the higher.

ITF found in LOCKED_ARMS (see entry Autorelock not working as expected); SNEB loop opened by the guardian.

At 7:00 UTC ITF in Maintenance mode, below the list of the activities communicated in control room:

• work on the SR and BS suspensions by SAT team;
• NE RH electrical checks by Flavio (see entry 68239);
• ENV activities in CB by ENV team;
• cleaning of the experimental areas by NIcola and external firm;
• ISYS checks in Laser Lab by Piernicola;
• TCS chiller refill by Ciardelli;
• standard tasks performed by the operator:
  • lock and scan of the OMC in NI single bounce;
  • TCS thermo cameras references;
  • TCS power checks:

All the activities concluded around 11:30 UTC; after some failed attempts the ITF relocked in LN3 at 12:46 UTC. To reach LN3 it was necessary to misalign the SR TY +2 at the end of CARM_NULL_1F.

At 13:49 UTC the ITF was manually unlocked and put in NI single bounce with SR and PR aligned for the planned activity of HWS-DET EM reflection by Ilaria from remote; then it was requested to align also the NE.

Activity in progress...

SBE

SNEB loop properly closed.

This morning a setup was installed to resume the investigation of the magnetic or seismic coupling path of the 401 Hz line visible in the sensitivity, attributed to the turbo pump of the DET/INJ tower (VIR-1098A-25). The plan is to inject a seismic and a magnetic line close to the frequency of the peak.

Near the DET turbo pump, the amplifier was left powered and the small coil connected to it (the shaker will be installed later), see Figures 1 and 2. For the injections, the DAC dedicated to acoustic injections in the Central Building will be used (DAQ BOX 30, SM 21, ch 7). The corresponding cable was left on the floor, near the rack (Figure 3).
The monitoring channel for the coil current is ENV_PROBE_CURR_MON (fs = 20 kHz). The coil was cabled to the DAQ room (ADC7674, Moni0 46, ch 10). The setup was tested by injecting a 25 Hz line, confirming that the system is working properly (Figure 4).

today, profiting of the fact that we had to unlock in order to let Ilaria do her commissioning activity, we made few tests restoring the BS tx in full bandwidth. The first test didn't go well as concurrently with the loop engagement we had a huge drop of the BNS (not clear if the drop is related to some loop misbehaviour, since the decrease of the BNS seems to be started before the fbw engagement, fig.1).

The second test we had a similar drop after 60 seconds the fbw engagement, but this time the issue was caused by a glitch on the local control signals, both on tx and ty, see fig.2 and 3 for zoom. By looking at the zoom they look more like some missing samples.

After the troubles on BS/IB of Sunday and the saturation of  the PR vertical coils of yesterday, PR and SIB1 positions have been recovered.  However, also the PR_X DoF moved by ~30µrad, bringing the BPC_TY close to the saturation. 

Today, at around 13.42UTC, once in LN3 we moved back the PR_X to reduce BPC corrections. TY corrections reduced as expected, nevertheless they may require an additional PR movement in order to bring them in a safer region. 

This morning, Flavio checked the connectors of the NE RH to investigate the temporary instability observed in the current flowing through one of the two glass rings  (see entry 68231).
 A visual inspection did not reveal any obvious issues. He then measured the current flowing through the various cables using a clamp ammeter (see first figure). During the measurement, small transient fluctuations were observed (see second figure).

To identify the module corresponding to RH1 — the one showing the unusual current behavior — I temporarily switched it off. It was confirmed that the module is the one on the right side of the first figure (the one with the red wire). Together with Flavio, we decided to leave the clamp ammeter installed to monitor the current during any future instabilities.

Tonight I found the ITF safety tripped after 5 failed lock acquisition attempts; however, after setting correctly the failsafe state (LOCKED_ARMS_IR), the automation immediately requested LOW_NOISE_3 again (Figure 1).

This has happened already a couple of nights ago (Figure 2): I think it's a bug of the newer Autoscience feature, there will be some investigations offline tomorrow.

I put the ITF manually in LOCKED_ARMS_IR.

Figure 1. Today I have tried a large exploration of the PRCL offset to see if that can increase the sideband gain. I also have adjusted the MICH offset to keep the sideband balanced on B1p, as a bad interference on sidebands will mean a lower gain. Even for large offsets (60) the impact on the sideband gain has been small, maybe a 5% increase, and not very clear. For large offset the power of the carrier started to decrease by 10%, which makes sense as for a strongly detuned PRCL the recycling of the carrier will not be as good. The time series starts just after a relock, and I have tried to cut out of the picture most of the transient at the beginning of the lock.

There are a couple of other things that improve slightly for a large PRCL offset, the DCP might be increasing from 420Hz to 430Hz, and the B1p power decreasing by 10-20%. But at the same time the 56MHz sideband becomes very misbalanced on B4, with 40% more power on the LSB than the USB. In fact the relative power between the 56MHz LSB and USB on B4 is the only quantity that looks very well correlated with the PRCL offset. 

This quite different from measurements done last year where an offset of PRCL of ~10 could change the sideband power by a few percent https://logbook.virgo-gw.eu/virgo/?r=64109.  However, that measurement was done in LN3, and the sideband gain was 30% higher to start with for the 6MHz sideband. 

It doesn't look like the PRCL offset is going to be a magical solution to solve the problem that the sideband gain in CARM NULL / LN is much smaller than expected based on defects in the mirrors + CP defects + point absorbers (VIR-0870A-22). It might still be worth check what happens in LN2 or LN3, to see if the behavior has changed compared to last year.

During the weekend I noticed that the SSFS UGF is quite lower than usual; looking back (Figure 1), it can be temporally correlated to the change of the IMC TF on Nov 20.

Looking also at the FmodErr tuning this morning (FIgure 2) it can be seen that both calibrations (MC_Z and LNFS) are underestimated, as after each tuning there were additional tunings to perform; this is not dangerous, unlike a big overestimation of the calibration, as in this case the tuning would diverge in a bang-bang correction

A previous FmodErr tuning (Figure 3) showed a good calibration.

Here's another example dating back to input laser changes in early 2024, when a 50% improvement in contrast defect follwed a tuning of WI DAS power.

Today we performed a series of noise injections on SDB1 to obtain the transfer function of the marionetta. We note that the interferometer was not locked during these tests.

We generated white noise using NOISE_flt with an amplitude of 1 V/√Hz, applied a 1–10 Hz band-pass filter, and injected the signal in the TY direction. However, we were unable to observe any clear response in SDB1_LC_TY above 5 Hz, including when attempting injections at slightly higher frequencies (see Figure 1 - TY.jpg). This injection ran from 11:35:03 UTC to 11:40:09 UTC. 

We then performed a second injection in the TX direction from 11:44:41 UTC to 11:50:15 UTC. With the same amplitude, we observed a somewhat larger response in SDB1_LC_TX  (see Figure 2 - TX.jpg), along with some apparent coupling into the TY direction (visible as a small feature in SDB1_LC_TY). However, this could also be due to LVDT readout noise rather than genuine bench motion.

We still need to analyse the data to determine whether these injections are useful for our purposes. If not, we may need to repeat the injections with the interferometer locked, possibly in a configuration such as CARM_NULL_1F to allow for higher-amplitude injections if needed.

ITF found in Troubleshooting mode with the following issues:

• BS loops opened, problem know: 68224.
• PR vertical correction saturating; to be recovered by the experts.
• SIB1 IP open; likely because of the previous problem.
• SPRB and SWEB vertical correction to be recovered.
• temperature in NE and WE outside the thresholds; to be investigated.

At around 8:00 UTC I recovered SIB1, SPRB and SWEB: in parallel Davide went to the END buildings to adjust the set points of the boilers.

At around 10:00 UTC the SAT team went in CB to work on the BS.

At around 10:30 UTC Paolo recovered the PR suspsension: after that I recovered the aligment of the north cavity and I was able to lock it on the IR.

At around 10:30 UTC Romain started to perform some noise injection on the DET bench.

At around 10:45 UTC the SAT team recovered the BS suspension; after that I manually realigned the WEST cavity and I was able to relock the ITF on the IR restoring the automation.

The BS suspension failed again at around 11:40 UTC;  situation in progress.

Software

BacNet restarted at 10:02 UTC because it was providing flat data.

SBE

SNEB loop closed and vertical position with step motors at 10:15 UTC

The current reading on the NE ring heater shows frequent drops since several months, corresponding to power changes of a few tens mW - up to ~200 mW in the worst case. According to the optical calibration with FRS scans, these should create RoC changes up to 0.5 m. 

Figure 1. On the night from Saturday to Sunday there were lots of lock losses occuring in the middle of ACQUIRE_LN3. The lock loss monitor reports them as BS TX loop gain to high, and looking at some of the figures there is indeed a BS TX oscillation starting 10-15 seconds before the lock loss. It starts probably when the BS TX loop is put into high bandwidth.

I report the result of the LSC injections done for W45, with GPSs 1446065205 (01/11) and 1446486805 (06/11). Here attached the projections on DARM and Hrec for both of them.

The noise budget is not particularly different than the recent ones: CARM is the most impacting contribution to DARM, while it's not the case in Hrec, as the reconstruction takes care of it by looking directly at the single mirror corrections. On Hrec, MICH is the most limiting one despite the two subtractions we have.

The attached plot shows an example of the impact of DAS tuning on carrier contrast defect. Carrier contrast defect is computed as the ratio of calibrated B4 power to calibrated B1p carrier power, where the fraction of carrier in B1p is extracted from the B1p phase camera. Data refer to the DAS tuning done after WE mirror replacement, and span from June 10 to August 17 2025, i.e. after the ETM RH tuning was over. 

Note that the Coeherence between the two nearby sensors (ENV_CEB_SEIS_V and ENV_CEB_ACC_V) is reduced during the acoustic injection in CEB