ITF found locking to LN2 with IPATSiA activity ongoiong. Since SR had just been aligned, it required some misaligning (+2 urad ty over 120 s) during CARM_NULL_1F timer.
15:30 UTC ITF in LN2, 30 Mpc
19:08 UTC end of IPATSia activity
19:21 UTC ITF in SCIENCE, autoscience ON
22:00 UTC ITF left in SCIENCE

Since the BS Voltage Monitor were not connected when the board was replaced a few days ago, the DMS flags/emails associated to the BS Voltage Monitoring have been shelved, until January13th (under Calib_Hrec / CalBS ).

On site: Suzanne, Piernicola, Manuel

Remote: Luciano, Ilaria

This morning, we performed HWS-INJ acquisitions to measure the optical path variation induced by the CO2 PA.

The HWS-RC acquisitions were done for different CO2 PA positions. 
Before starting, we moved the CO2 PA in the opposite direction wrt the Position 2 described in the entry 68291, we will called it Position 4 (see fig. 1).  

We started by applying approximately 40 mW, instead of the 50 mW used in 68291.

Position 4   

The HWS-INJ SLED ON at 1.63 V.

The CCD illumination is shown in Figure 2. 

ITF configuration: LN2 achieved at 09.20 UTC

Start acquisition:  09.56 UTC (Folder 20251203T1056)

IPATSiA ON: 10.01 UTC (WF 13)

Unlock at 10.07 UTC (WF 26)

IPATSiA OFF: immediately after the unlock

HWS-INJ acquisition stopped at WF 27.

The CO2 PA immediately appears in the HWS-INJ map (see Fig. 3). For convenience, the same figure also shows the HWS-INJ image with the YAG on the WI mirror.

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Since the impact of the CO2 PA was destructive and the ITF unlocked very quickly, we decided to move the CO2 PA to Position 1 described in entry 68291, as in this position the ITF was able to maintain the lock.

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Position 1-HP (the same Position 1 as during Monday’s shift)

ITF configuration: LN2 AT 10.39  UTC

Start acquisition:  10.50 UTC (Folder 20251203T1150)

IPATSiA ON: 11.01 UTC (WF 29)

Unlock at UTC 11.05 (WF 41)

HWS-INJ acquisition stopped at WF 42.

The CO2 PA immediately appears in the HWS-INJ map (see Fig. 4). 

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Again, the ITF unlocked very soon. So we decided to decrease the power injected up to 10 mW.

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Position 1-LP (same as before, but with 10 mW of injected power)

ITF configuration: LN2 achieved at 15.30  UTC

Start acquisition:  15.44 UTC (Folder 20251203T1643)

IPATSiA ON:  15.48 UTC (WF 12)

The CO2 PA immediately appears in the HWS-INJ map (see Fig. 5).

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Without closing the flip mirror, at 16.32 UTC (WF 129), we moved the CO2 PA in Position 4-LP.

After half an hour (at 17:03 UTC, WF 212), the CO2 PA was moved in the same direction as before by the same number of steps (10000) [POSITION 5-LP].

After another half hour (at 17:36 UTC, WF 300), the CO2 PA was moved again in the same direction by the same number of steps (10000) [POSITION 6-LP].

%%%%%%%%%%%%%%%%%%%%%%%%%
IPATSiA OFF: 18.07 UTC (WF 383) [FLIP MIRROR CLOSED]

The HWS maps for each data set are summarized in Figure 6.
Then, Piernicola went to the CEB to switch off the entire IPATSiA setup (laser+CH).
He came back at 19.08 UTC / activity concluded.

In this log entry, we use the following naming convention for surveyed points (three per platines): 

Each platine is named after the first two letters of the near rotor + 1 character which is "T" for the point above the rotor, "N" for the surveyed point nearest to the Near rotor, "F" for the last surveyed platine point (further away fro the near rotor)

The "transation" between  this convention and the one from the log entry 68205 is as follows:

WNT = WE_Ncal_NB_06-T
WNN = WE_Ncal_NB_03-SW
WNF = WE_Ncal_NB_04-NW

WET = WE_Ncal_NB_05T
WEN = WE_Ncal_NB_02-SE
WEF = WE_Ncal_NB_01-NE

WWT: WE_Ncal_SB_05-T
WWN: WE_Ncal_SB_04-NW
WWT: WE_Ncal_SB_03-SW

WST = WE_Ncal_SB_06-T
WSN = WE_Ncal_EB_01-NE
WSF = WE_Ncal_EB_02-SE

In this log entry, we use the following naming convention for surveyed points (three per platines): 

Each platine is named after the first two letters of the near rotor + 1 character which is "T" for the point above the rotor, "N" for the surveyed point nearest to the Near rotor, "F" for the last surveyed platine point (further away fro the near rotor)

The "transation" between  this convention and the one from the log entry 68206 is as follows:

NET = NE_Ncal_EB_05T
NEN = NE_Ncal_EB_03-SW
NEF = NE_Ncal_EB_02-SE

NWT: NE_Ncal_WB_05-T
NWN: NE_Ncal_WB_01-NE
NWT: NE_Ncal_WB_04-NW

ITF found relocking arms but N cavity was misaligned. I realigned it and restarted the lock acquistition up to LN2 for the planned LN2 IPATSiA activity (Melo, Spinicelli).
After the usual cross-alignment in ACQUIRE_DRMI, I misaligned SR about 2 urad in ty+ at CARM_NULL_1F.
COMMISSIONING mode set. LN2 acheived at 07:41 UTC at 1st attempt.
08:00 UTC started the activity.

Unfortunately ITF is particulary unstable.
After several unlocks and relocks, at 13:07 UTC the unlock opened the WI LC loop. Properly closed.
Relocked at LN3. Activity in progress...

Since few days, the BPC TY corrections were quite high, very close to their limit. 

In order to reduce them, at around 11.20UTC we moved the PR_X by +40µrad, centering at the same time the beam onto the ITM.

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.