Motivations for the shift :

This logbook presents only the measurement. The analysis and the results will be presented later.

In this shift, we made scans to characterize the arms. We first ran a series of scans with the mirrors well aligned in order to estimate the amplitude of astigmatism. Then, a lot of scans were made with different pairs of orthogonal misalignment axes in order to measure the orientation of astigmatism. The aim was to do the same scans as presented in 66820, but the measurement presented in this logbook concerns only the north arm since it was made during the change of the West end mirror. During the previous measurement, ramps were generated by variation on ALS_NEB_Corr rather than LSC_CARM_INPUT in the usual method used today. When we made those single cavity scan, we observed that the data were noisy such that we were not able to conclude concerning the orientation of astigmatism. 

Shift report

Date of the shift : 2th December 2025

To do the scans, we followed the process described in the Optical Characterization wiki page (section : FSR slow scan (with the green laser)):

All the scans were run with the command CARM_SET_scan_FSR(numiteration = 10, f_FSR=110000,timescan = 60.) Each iteration corresponds to one descending scan and one ascending scan. The misalignment angles used were chosen such that the total amplitude is equal to 0.5urad. This high amplitude was chosen to make the misalignment that we chose significant compared to the one usually observed during 'aligned' scans. Then we expect the position of the first higher order mode to be more representative of the orientation of the misalignement axis used. 

The arms unlocked during the last scans presented in the table above. After many attempts, we were not able to run the scans again with the misalignment angle we planned. Starting at 18:32 UTC and for 20 minutes, we made scans with no misalignment to check if the problems came from the misalignment applied. All the scans were performed correctly, suggesting that the amplitude of the misalignment was the problems.

In order to continue the measurement, scans were made with smaller misalignment, keeping the same orientation for the misalignment axes but with a total amplitude of 0.3urad rather than 0.5urad.

The data will be analyzed soon and presented in another logbook

ITF found in Commissioning mode for the planned activity of cold arm FSR scan by Jacquet, Goodwin-Jones from remote; activity concluded at 21:18 UTC.

After that I launched the lock acquisition; it was necessary to manually prealign PR and SR and then to apply SR Ty +2 in CARM_NULL_1F.

ITF left locking to LN3 with Autoscience enabled.

This morning, following the turn off of the air conditioning in the CEB, I was called by the operator to monitor the status of CEB towers. Looking at the data, the Y correction of SR F0 was close to saturation. To prevent the temperature transient from saturating the correction and disturbing the activities planned for the afternoon I adjusted the vertical correction of the tower.

Intervention start time: 10:34 local time

Intervention end time: 11:15 local time

Right after the end of my intervention Boschi and Palaia performed a measurement of the vertical transfer function of the SR tower.

Measurement start time: 11:21 local time

Measurement end time: 11:36 local time

The coordinates of the survey carried out on November 20 have been recalculated due to an error in the settings of the parameters for the Best Fit transformation. The correct coordinates are now shown in the attached table (NE_NCal_Tab.1_corr).

The coordinates of the survey carried out on November 19 have been recalculated due to an error in the settings of the parameters for the Best Fit transformation. The correct coordinates are now shown in the attached table (WE_NCal_Tab.1_1_corr; WE_NCal_Tab.1_2_corr).

Yesterday we started to work on the IPATSIA after the installation in the CEB area, currently on the WI tower. 

We switched on the CO2 laser at 9:55 UTC, waiting some time for the laser thermal stabilization at around ~50mW of injected power.

We then started shining the mirror at 11:22 UTC with the ITF in LN2 since ~10:00UTC (BS put in full BW manually each time). To be noted that during the first part of the LN2, the SR has yet to recover the aligned position because of the needed disalignment trick to reduce B1p power. Its regime state is reached several minutes later. 

Fig. 1 shows the thermal image of the mirror before the PA (ITF locked) and Fig. 2 shows the image after we started shining the mirror in the first position. In Fig. 3 we have the same position, after one hour of shining, with a different palette, that we used for the rest of the images. As we can see in the two figure, a simmetric spot (wrt the mirror center) appears together with the CO2-PA. This is similar to what we found in one of the position at the WE (see fig. 4 in #67670), and not understood yet. 

Right after the injection of the CO2-PA, we had a huge instability of the ITF because of a glitch on the SR_AA signals and, as a consequence, OMC alignment. The effect of the CO2-PA was anyway visible with an almost  ~9% of reduction of the power circulating into the arms. The DCP moved away and came back only after ~22 minutes.

In this position, the CMRF was very high and the sidebands very low. After two hours of lock, we tried to compensate adding offset on the BS_AA. Unlike what usually happens, adding offset on the TY didn’t help at all. Changing the BS_TX_SET in the negative direction did help, but it also increased the B1p power. With the BS_TX_SET, the ITF was even more unstable (see Fig. 4).

At 14.15 UTC we stop moving the BS, the CMRF was quite ok and we wait there for some time to acquire data in this condition. The offset has been removed at 14.45 UTC.

We than moved directly the CO2-PA to another point (10k picomotor steps in the vertical lower direction, the camera being upside down, which should correspond roughly to 8mm w.r.t the previous position). At 14.52 UTC we started shining in the second position (see Fig. 5). We waited there for half an hour to acquire data.

At 15.30 UTC we moved again the CO2-PA from the same amount as before in the vertical direction, adding another ~8mm (see Fig. 6), but the ITF unlocked immediately after. We stoped shining at 15.32h and we waited the ITF to lock in LN2 again. 

At 16.45 UTC we started shining again in the third position, after the ITF recovered the LN2 state but at 17.00 UTC the ITF unlocked again and we turned up the flip mirror and stop shining the CO2-PA. We tried one last time to recover the ITF to acquire some data, started shining at 17.56 UTC but at 18.06 UTC the ITF unlocked again and we stopped there.

Fig. 7 shows a summary of the main DoF of the entire shift, till the last unlock.

Few comments: 

• Working on the input mirrors seems to have a stronger impact on the ITF, mainly on the CMRF and on the sidebands. Estimating the amount of 1/f^2/3 noise will be more complicated. 
• At each injection of CO2-PA, whatever the position, the DCP estimation changed (both the ISC and the Hrec one). Only for the first position it happened together with a glitch on the SR AA which eventually caused an instability of the ITF. The DCP took several minutes to recover its value, and the same for the BNS range (see Fig. 8). This effect seems to correlate well with the SR_TY position. Arm power and sidebands are not affected.
• The CMRF and the othere DoF are less affected by the CO2-PA as far as we go away from the center of the mirror. However, for the last position the lock lasted barely few minutes (only 1' the first time and less than 15' in the last two attemps). The ITF was quite robust either before and after this position (it remained locked all the night long).
  This may indicate that we excite some instabilities once in this position (some specific HOM?). 

7:00 UTC ITF in MAINTENANCE

Tasks performed:

• OMC scan (operator)
• AHU maintenance (Nenci)
• TCS chiller refill (Ciardelli, Menzione)
• Weekly cleaning (cleaning company)
• Neovan Chiller swap (Gosselin, De Rossi)
• NE Ethernet serial bridge replacement (De Rosa)
• PR accelerometer adjustment, SR adjustments (Baratti, Boschi, Piendibene)
• Etalon Setpoint change, NI 19.29, WI 19.74, three-day ramp (Mantovani, operator)
• TCS Thermal Cameras check (Lumaca, operator),slight  adjustment of NI CH (Lumaca)
• TCS Power Check (Lumaca, operator)

11:00 UTC realignment of WI, WE, PR, SR
11:45 UTC ITF in COMMISSIONING, LOCKED_ARMS_IR, ready for 12:30 cold arm FSR scan
12:30 UTC cold arm FSR scan (Jacquet, Goodwin-Jones). ITF.LOCK set to MANUAL

This morning we replaced the serial-network bridge used to manage the weather station at NEB. After the replacement and the server restart all the signals were back. The plot shows a comparison between the three weater stations: after restarting the server, all the values became compatible, except for the wind data from the NEB station.

The wind sensor at the NEB station needs to be checked again.

The NCal and associated PCal lines have been moved to the 72-72.5 Hz range (except NWN which is at 36.08 Hz) around 12:30 UTC, while the ITF was not locked.

This morning, around 11:20 UTC, I restored the microphone installed in EER (ENV_EER_MIC). The intention was to substitute the amplifier as suggested in 67031 , but after the inspection I realized that the problem arose because of a bad connection between the microphone and its amplifier. Now the connection was restored and the signal is back.

In the plot the blue curves represent the current situation, compared with the last working condition (magenta curves), and the past situation (orange curves) with the bad connection. Hence the sensor and the amplifier are still the same.

After switching from the main chiller to the spare unit two weeks ago, we observed a temperature oscillation in the neovan head. This fluctuation was also visible in the DC powers downstream: in the INJ/PSL ones and but also the ITF ones (see attached Figure 1).

This morning, we went back to the chiller room to reconnect the neovan head to the main chiller. We managed to perform the swap quickly enough to avoid triggering the Neovan head temperature safety.

Note for future interventions:
It is important to prime the chiller pump before switching it on by pulling the red priming handle on its front panel. It prevents the usual flow-error warning when powering the chiller back on.

After the swap, the temperature stabilized again around 29.6 °C (Figure 2). This value is higher than with the spare chiller, but without oscillations. We will continue monitoring the temperature over the next few days.

Part of Thursday’s shift will be dedicated to realigning the beam on the LB, particularly in the neovan head, which should slightly reduce the temperature.

Two months ago there was the surprising measurement that the BNS range improves by 3Mpc (~10%) when the OMC mode matching is made worse on purpose https://logbook.virgo-gw.eu/virgo/?r=67850

To test that the interefrometer relocked in LN2 I have put BS TX in highbandwidth and moved SDB1 along the Z direction, without waiting for SR to fully realign.

Figure 1 shows the trend of the data for the part of the motion after SR has finished realigning (DARM response pole stable around 420Hz). The bench has moved by the same ~4mm as in October, the optical gain decreased this time by ~10% instead of ~5%. The BNS range did not improve, it has actually gotten slightly worse. The frequency noise coupling was also worse, and the dependence of the amount of DARM signal (491Hz line) detected in reflection of the OMC (B1s) was very clear, with the zero for SDB1 LC Z at 2000um, while the nominal position of the bench is 3700um.

Figure 2  for comparison is the trend of the same channels during the test from October 2. In that case the frequency noise coupling was getting slightly better, and the amount of DARM signal on B1s changed by a factor 4 less. 

The situation is clearly different that what it was in October, but we also know that the defects working point of the interferomter has changed at the end of October for reasons we don't understand, and it is much worse. For example the power on B1p in LN2 is ~370mW instead of ~250mW.

The bench was put back to its initial position, at the end of the scan there was some glitch that kicked the SR alignment that I removed from the figure 1, that is why the last ~300um of bench position sweep are not shown.

ITF found in Science mode (for about 23h).

At 8:10 UTC I removed Science mode, then at 8:42 UTC I manually unlocked to relock in LN2 as requested by the planned commissioning activity of IPATSIA.

Activity in progress.

7:00 UTC ITF found in SCIENCE
During the night two unlocks happened, the first relock took four attempts and the second two - unsuccessful attempts at LOCKING_CARM_MC_IR and LOCKING OMC_DARM_B1_PD3
7:16 UTC unlock, WE_IP/F7/PAY red as well as LSC_B8_DC showing an oscillating pattern. Unsuccessful relock attempt at CARM_NULL_1F
8:16 UTC ITF in SCIENCE
15:00 UTC ITF left in SCIENCE

I checked the past data of WEB acoustic injections by inspecting the noise levels sent to the DAC: both in September (blue curve) and in November (green curve), the levels were identical. Therefore, it is not clear why an amplitude of 0.1 caused the interferometer to lose lock.

To safely perform the WEB acoustic injection, we keep the amplitude at 0.01 (pink curve), as done on November 27.

ITF found in relocking phase.

At 15:29 UTC it reached LN3 and the ENV activity could start, see entries: 68729, 68281

Commissioning activitiesy conclude at 19:27 UTC.

ITF left in Science mode with Autoscience ON.

In order to investigate the coupling mechanism of the 401 Hz peak to hrec, we injected a line at 405 Hz:

• Magnetic injection: using the small coil, varying its orientation, (Figure 3, 4, 5)

• Seismic injection: using the shaker at the same frequency.

Preliminary observations:
The injected line at 405 Hz is slightly visible in hrec for both magnetic and seismic injections, Figure 1 and Figure 2.
Looking at the coherence between hrec and the magnetometer (*DT_MAG*) on the DET tower base (inside lab), as well as the accelerometer (*DT_ACC*) on the flange, the magnetic coherence appears slightly higher than the seismic coherence.

The injection times are reported in the attached file.

This morning and in the afternoon (due to the ITF unlocks), a tapping campaign was performed in CEB. Specifically, tapping was applied on several flanges of each tower, on DET viewports, on SIB1 and SIB2 beam dumps, and on DET and INJ cryotrap vessels.

Only a few preliminary comments on what was observed during the tests (a complete analysis will follow)

SDB1 – South flange: Peak at 121 Hz and several additional lines.

Cryotrap – DET viewport (West side): peak at 315 Hz and various other frequencies

DET Cryotrap – Vessel: peaks above 400 Hz; clear peaks at 501 Hz and 843 Hz.

SR flange – East: peaks at 501 Hz and 840 Hz

SR flange – West: peak @ 120 Hz.

PR North flange (POP flange): peak at 730 Hz and minor lines around 93–105 Hz.

NI North flange: peak at 165 Hz, increasing and disappearing with delay  (~1 minute)

B1 viewport: Fluctuating line at 26.5 Hz, and peak at 66 Hz.

B1p Viewport: Strong broadband response: 115–120 Hz, 200 Hz, 322 Hz, and several additional lines.

Hartmann viewport: 66 Hz line shows slight breathing/modulation.

B5 viewport: responses above 400 Hz are more intense; additional lines at 101 Hz and 190 Hz.

EQB1 door: narrow peak at 951 Hz.

General observation: 
The 120 Hz line is persistently excited and fluctuating even without tapping, just by moving around the  SR -DET area.

Figures 1 and Fugure 2 show the spectrograms of hrec during the tappings performed in the morning and afternoon, respectively.

The time and the exact locations of each tapping are reported in detail in the attached file.

PS During the tappings in SIB2, we noticed a whistling noise caused by the compressed-air line (Figure 3). We informed Piernicola, who then contacted Antonio.

The OMC was not locking due to a change in sign of its error signal. This must be due to the reconfiguration of the EDB DAQ box:

2025-11-28-11h31m04-UTC    info masserot     Reconfigure EDB_DBOX_DetLab2 in SDB_EDB_dbox_rack

After changing the sign of both photodiode error signal (as usual for this type of problem), the OMC could lock. But we had afterwards two unlocks in ACQUIRE LN2. 

Figure 1 shows one example, it was odd as the OMC PZT correction is suddenly diverging from zero. Looking at the log of the automation it corresponds to the time when the OMC goes to low noise mode, which means use B1 PD2 instead of B1 PD3 as the error signal. And comparing both error signals they go in opposite direction.

So this time only the sign of B1 PD3 error signal change, while the one of B1 PD2 did not. This is new, both were changing together in the past ~5 times I have seen this problem.

After changing the sign of just the B1 PD2 error signal the lock acquisition could continue to LN3. Note that the B1 PD2 phase is still quite bad, as the I and Q signals are equal, so it is off by ~45 degrees. But I haven't touched it as I am not sure in which direction in needs to be changed.

The NCal and associated PCal lines have been moved to the 26-26.32 Hz range at 15:36 UTC, while the ITF was not locked.

DRAFT
ITF found in LOW_NOISE_3 and SCIENCE Mode, AUTOSCIENCE On.
UTC 9:09 COMMISSIONING Mode set for CEB viewport tapping (Tringali, Fiori);
UTC 10:45 Unlock. Relock to LN3 achieved at 11:26 UTC.
UTC 11:31 Unlock. Relock failed at first attempt (LOCKING_CARM_NULL_1F). Relock failed at second attempt (LOCKING_OMC_DARM_B1_PD3). Relock failed at third attempt (LOCKING_CARM_NULL_3F). At fourth attempt the sidebands were unbalanced and B1p was 0.035, once the CARM_NULL timer was over i lowered MICH_SET to 30 and added +1.8 urad to SR TY, the OMC was not still able to lock, I contacted DET oncall with no answer and then I contacted Was, activity ongoing. Another attempt was performed adding +2 urad ST TY ensuring B1p was in the correct range, ITF Unlocked at ACQUIRE_LOW_NOISE_2. ITF Unlocked one more time at ACQUIRE_LOW_NOISE_2.
ITF left in CARM_NULL_1F.
 

SInce the BS board replacement, the DMS flag monitoring the TF from Sc_BS_MIR_Z_CORR to the coil current monitoring channels (V1:Sc_BS_MIR_VOUT_DL and DR, UL, UR) is red.

Indeed, the VIM plots show that there is no coherence anymore between them at 2012 Hz (figure 1, top right).

Figure 2 : looking at the channels with dataDisplay:

- purple: current situtation (ITF locked)

- blue: situation on 24 November

--> It looks like we now see only ADC noise, and that the four VOUT monitoring channels are not enabled/plugged?