The temperature variation of NI and WI TMs under etalon control can be reconstructed assuming three components:

1. The effect of the YAG, following the lock/unlock of the cavities
2. The effect of the heater used in etalon loop
3. a compensation of a constant drift due to an external disturbance

A first attempt to do this reconstruction was done some time ago for NI, in a period when the control had some oscillation and the control correction was quite high. Using those data as a noise injection, it was possible to estimate the temperature response to the heater as two simple poles at 2.5 uHz and, on that estimation, develope a new more performing etalon controller. A good data reconstruction was possible assuming also a response to a YAG step as a simple pole at 2.5 uHz, with an amplitude 0.2 deg. Applying the same model to WI, the reconstruction did not work so well  as for NI, mainly due to a larger sensitivity to a YAG step.

The analysis has be replied, trying to be more precise in the evaluation of an alternative step response to the YAG for WI. Two different models have been tested:

1. simple pole at 2.5 uHz (the same as NI), amplitude 0.3 deg (50 % larger than NI)
2. simple pole at 5 uHz (the double of NI), amplitude 0.2 deg (the same as NI)

Among the two, it seems that the second model works better. I don't know how to explain a so much different time scale for the heat absorbtion/dispersion in two TMs which should be very similar.

An attempt to use a different response to the heater did not give any better result.

The models applied to old data (March) or recent data (October), give results of similar quality, excluding a relevant change in time of the responses.

Due to the external temperature decrease the Etalon loop corrections were saturated since the 22 of November

we decreased the set point of one fringe (for NI and WI) in 3 days NI to 19.543 and WI 20

Data analysis from broadband noise injection

First we have measured the FC length control loop gain by injecting 7-50Hz white noise in the LFC control; the 3e-2 amplitude noise injection was performed from 2025-11-04-10h46m22-UTC to 2025-11-04-10h50m23-UTC. The measured G(f) open-loop TF is shown in the first plot:

We then proceeded to measure the V-H coupling by injecting noise into the vertical actuator of the FCEM GAS filter. A summary of the 7-50Hz noise injection is shown in the following plot which includes the spectrum of the cavity length error signal, the FCEM vertical actuation signal, which is DC calibrated, and the coherence. The peak at 26.55Hz in the cavity length error signal corresponds to the vertical bounce mode of the mirror suspension.

By combining the actuation signal with the SUMCON model of the payload mechanics we have estimated the actual vertical displacement of the mirror; the conversion also included the compensation of the 35-Hz pole in the coil driver response. The open-loop cavity length change dL can be estimated as dL = 5e-13*LFC_GR_PD_RF_5MHZ_I_CAL * (1+G(f)), where the scaling 1Hz = 0.5 pm is applied. From the comparison between the two reconstructed signals, see next plot, we can extract a V-H coupling of 2e-4 which appears to be frequency independent in the explored band. This measurement was taken with the FCEM mirror Z-actuation not optimized in terms of balancing; for this reason we are planning to repeat it under better balancing conditions.

ITF found DOWN in COMMISSIONING with the activity on "BS board replacing" in progress (Boschi).
Activity concluded at 16:30 UTC.

We started to relock. After the usual cross-alignment in ACQUIRE_DRMI, and after several attempts, ITF unlocked always during LOCKING_ARMS_BEAT_DRMI_3F.
According with Bersanetti we decided to leave it in LOCKED_ARMS_IR.

The example from early 2024 is not very clean, as there is a differential change in EM RH correction 3 hours before the DAS power change. The RH response is delayed and has a few hours long time scale, so the effect othe DAS change will overlap with change in B1p carrier power due to EM RH which is well understood and modeled. 

A somewhat cleaner recent example of B1p power change with DAS tuning in LN3 is from the tuning to try to recover from the not understood change in interferometer state in October: https://logbook.virgo-gw.eu/virgo/?r=68015

Yesterday evening, at 19:10 UTC, the PR CHRoCC was switched OFF in preparation for this morning’s HWS-INJ measurement (entry 68252).

This morning, I switched OFF the HWS-DET SLED and switched ON the HWS-INJ SLED at 1.63 V.
The HWS illumination before starting the measurement is shown in figure 1.

ITF configuration: WI Single Bounce + PR aligned (PR MAR TX=-44.6 urad, PR MAR TY=-17.5 urad taken from carm null data)

Start HWS-INJ acquisition: 07.58 UTC (Folder 20251126T0858)

At 08:08 UTC the PR CHRoCC was switched on. The CHRoCC power was set to 0.7 V × 9.4 = 6.58 V, applied with a 1800 s ramp.

The factor 9.4 is the result of calibration described in 60539.

Some wavefronts acquired during the measurements are shown in figure 2.
The curvature extracted today is slightly lower than the values from 2022-07-29  and 2023-01-16 (58436 and 58441) (see Figure 3).
A comparison of the applied heater voltage and current with past measurements shows that they are lower, as if the 9.4 coefficient were underestimated (see Figure 4).
However, all observables are consistent: lower voltage leads to lower current, smaller temperature changes in the heater, and a correspondingly reduced curvature induced by the CHRoCC.

For reference, the signals from the local controls of BS, PR, WI and WE during the measurements are shown in Figure 5.

In conclusion, the shape of the OPL variation induced by the CHRoCC and the resulting curvature are consistent with previous measurements.
At 13.29 UTC, the PR CHRoCC voltage has been decreased to the nominal one, i.e. 4.19 V with a ramp of 1800 s.

7:00 UTC ITF found in COMMISSIONING, LOCKED_ARMS_IR
7:58 UTC TCS measurements: ITF put in SINGLE_BOUNCE_WI with PR manually aligned - metatron node still in MISALIGNED (+25.5 urad Ty) for HWS measurements (4hrs, Nardecchia)

1. Measurement with CHROCC tension 6.58V (9.4V times 0.7 factor, ref. to 2023 measurement)
2. CHROCC set back to 4.19V (value as of 30/10/2025)
3. PR manually misaligned to previous setpoint

14:30 UTC ITF in DOWN for SUS activity: BS board assessment/replacement (Boschi)

No DMS Events Monitoring to report

From this image, examining the signals

• Sa_BS_F0_LVD_H1_min_TIME
• Sa_BS_F0_LVD_V_min_TIME

a significant reduction of the glitches can be observed after approximately 11:00 UTC.

Below the report the ISC_Fb server related to Sc_BS data for

• the 2025-11-25 after  10h00-UTC
  • 2025-11-25-11h21m04-UTC>WARNING-[TfbSubFrame::Fill] GPS: 1448104882.200000000 - Source Sc_BS: 3/2000 missing packet(s), 1 data break(s)
    2025-11-25-11h47m29-UTC>WARNING-[TfbSubFrame::Fill] GPS: 1448106466.800000000 - Source Sc_BS: 116/2000 missing packet(s), 0 data break(s) (missing data are at the end of the vector)
    2025-11-25-11h47m29-UTC>ERROR..-[TfbSource::StoreData] producer Sc_BS: overflow at GPS 1448106467.199913050 (received 2116 / expected 2000) (6844 times)
    2025-11-25-11h47m53-UTC>WARNING-[TfbSubFrame::Fill] GPS: 1448106491.400000000 - Source Sc_BS: 397/2000 missing packet(s), 1 data break(s)
    2025-11-25-11h48m07-UTC>WARNING-[TfbSubFrame::Fill] GPS: 1448106505.600000000 - Source Sc_BS: 370/2000 missing packet(s), 1 data break(s)
    2025-11-25-11h53m46-UTC>WARNING-[TfbSubFrame::Fill] GPS: 1448106844.600000000 - Source Sc_BS: 395/2000 missing packet(s), 1 data break(s)
    2025-11-25-11h54m27-UTC>WARNING-[TfbSubFrame::Fill] GPS: 1448106885.000000000 - Source Sc_BS: 355/2000 missing packet(s), 1 data break(s)
    2025-11-25-12h02m56-UTC>WARNING-[TfbSubFrame::Fill] GPS: 1448107394.600000000 - Source Sc_BS: 2/2000 missing packet(s), 1 data break(s)
    2025-11-25-12h03m04-UTC>WARNING-[TfbSubFrame::Fill] GPS: 1448107402.000000000 - Source Sc_BS: 195/2000 missing packet(s), 0 data break(s) (missing data are at the end of the vector)
    2025-11-25-12h03m04-UTC>ERROR..-[TfbSource::StoreData] producer Sc_BS: overflow at GPS 1448107402.399912730 (received 2195 / expected 2000) (11505 times)
    2025-11-25-14h15m33-UTC>WARNING-[TfbSubFrame::Fill] GPS: 1448115351.400000000 - Source Sc_BS: 212/2000 missing packet(s), 0 data break(s) (missing data are at the end of the vector)
    2025-11-25-14h15m33-UTC>ERROR..-[TfbSource::StoreData] producer Sc_BS: overflow at GPS 1448115351.799912740 (received 2211 / expected 2000) (12449 times)
     
• the 2025-11-26 night
  • 2025-11-26-02h39m47-UTC>WARNING-[TfbSubFrame::Fill] GPS: 1448160005.400000000 - Source Sc_BS: 70/2000 missing packet(s), 0 data break(s) (missing data are at the end of the vector)
    2025-11-26-02h39m47-UTC>ERROR..-[TfbSource::StoreData] producer Sc_BS: overflow at GPS 1448160005.799912770 (received 2069 / expected 2000) (4071 times) 
    2025-11-26-02h58m10-UTC>WARNING-[TfbSubFrame::Fill] GPS: 1448161108.800000000 - Source Sc_BS: 400/2000 missing packet(s), 1 data break(s)
    2025-11-26-03h18m53-UTC>WARNING-[TfbSubFrame::Fill] GPS: 1448162350.800000000 - Source Sc_BS: 396/2000 missing packet(s), 1 data break(s)
    2025-11-26-03h36m28-UTC>WARNING-[TfbSubFrame::Fill] GPS: 1448163406.600000000 - Source Sc_BS: 343/2000 missing packet(s), 1 data break(s)
    2025-11-26-04h04m12-UTC>WARNING-[TfbSubFrame::Fill] GPS: 1448165070.200000000 - Source Sc_BS: 388/2000 missing packet(s), 1 data break(s)
    2025-11-26-04h14m49-UTC>WARNING-[TfbSubFrame::Fill] GPS: 1448165707.000000000 - Source Sc_BS: 264/2000 missing packet(s), 0 data break(s) (missing data are at the end of the vector)
    2025-11-26-04h14m49-UTC>ERROR..-[TfbSource::StoreData] producer Sc_BS: overflow at GPS 1448165707.399912810 (received 2263 / expected 2000) (15517 times)
     

According to these messages, It seems that the Sc_BS data are not correctly sent by the Sc_BS DSP . There are missing samples and more from time to time

• 025-11-26-02h39m47-UTC>WARNING-[TfbSubFrame::Fill] GPS: 1448160005.400000000 - Source Sc_BS: 70/2000 missing packet(s), 0 data break(s) (missing data are at the end of the vector)
  2025-11-26-02h39m47-UTC>ERROR..-[TfbSource::StoreData] producer Sc_BS: overflow at GPS 1448160005.799912770 (received 2069 / expected 2000) (4071 times)   
  • for each channel of the 59 Sc_BS'ine, 69 more sampling were received : 69*59 = 4071 times as it 's a tagged message
• idem for the  2025-11-26-04h14m49-UTC report

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.