ITF DOWN in UPGRADING
Activities carried out this morning:

• Check of EER temperature: eurotherm sensor read 19.4 °C, ENV_EER_TE 16.8 °C. Room conditions were fine, ENV experts were notified (Andreazzoli, Tringali)
• TCS chillers water levels check (Ciardelli)
• SR RH was switched on and switched back off (68434 Nardecchia)
• TCS Aux Lasers cooling tank filter maintenance (68435 Ciardelli, Zaza, Nardecchia)
• SR tower pumping in progress (Vacuum team)

At around 13:30 UTC, INJ unlocked and EIB started oscillating. No seismic activity. I contacted INJ experts, relock in progress (Spinicelli).

After noticing a negative drift in TCS_AuxCooling_NI_FLOW (picture 1) we turned off both WI and NI aux lasers and proceeded to extract and regenerate the filter, whose condition before and after can be seen in picture 2 and picture 3. Water flows were restored, NI aux laser PWRLAS went back to its working point, WI PWRLAS recovery is still ongoing.

The RH was switched off after Antonio reported that the pressure was 20 mbar; RH operation is not allowed before 4 January. 

At 08:51 UTC, the SR RH was switched on at the usual power (V = 23.13 V, I = 0.34 A).

A set of plots illustrating for each tapping location the effect on hrec and on the accelerometer closest to the tapping location. Missed in previous entry: a location that produced a quite large effect in hrec was DT cryotrap viewport. 

ITF found in UPGRADING Mode with both arms locked on the IR.
7:13 UTC MAINTENANCE Mode set.
List of activities comunicated or performed by the operator during maintenance:
- End terminal buildings pipes replacements (Andreazzoli).
- 9:20 - 9:39 TCS Thermal Camera References; 
- 9:50 - 10:04 TCS CO2 Power Checks;
MAINTENANCE ended at 11:00. UPGRADING Mode set back.
Pumping of the SR tower started this morning (see #68431).

TCS CO2 Power Checks (measured at CH Pickoff): 

This morning the SR tower has been cleaned (standard cleaning) and then closed. The pumping is in progress.

ITF found in UPGRADING with arms locked.
All times are UTC.
7:07 SIB2_SBE closed.
7:20 TCS Chillers guardians opened due to WI TCS Chiller Head Replacement in TCS room (Ciardelli, Zaza). Activity concluded at 8:10 (see entry #68428).
7:55 Process LNFS100 in "VPM > Injection > ISYS Sms Bridges" unable to be restarted. Following the instructions of entry #67072, the process was alive in olserver129, I logged in as virgorun and I killed existing processes, then I restarted successfully the process on VPM (see Figure 1).
From 7:22 Process TCSChillerWI in "VPM > TCS > TCS room" was orange with "Timeout from worker process!" error, I tried to restart it with no success. I logged in olserve133 as virgorun and I killed existing processes, then I restarted successfully the process on VPM (see Figure 2), then I restarted FbsMoni process in "VPM > Data Collection > Front End DAQ". This issue was probably generated by the WI TCS Chiller Head Replacement (see entry #68428).
SR baffle installation ongoing, baffle is installed and balancing is ongoing (Majorana). Activity concluded at 16:38. 
16:48 Thresholds adjustments of Sc_NE_MAR_PSDM_PWR_50Hz and Sc_NE_MAR_PSDT_PWR_50Hz flags under DMS > Suspensions > NE_PAY (Majorana).

The head (AC200) of the WI A40 thermochiller in TCS chiller room (part of the TCS chiller guardian system) was replaced because it was making a loud noise. The replaced head showed signs of oxidation.
Flow and temperature values remain unchanged at 3.4 l/min and stp 19.00 °C.

ITF in UPGRADING, state DOWN
7:40, 12:26 UTC INJ unlocks (kept happening for about one hour in the second case), relocked shortly after. Wind activity on site, seismon flag red, sea activity flag yellow.
Issues with left and det telescreens fixed (Kraja, Salconi)
 

Here we illustrate some results of tappings in the central area. In the TABLE we list the most sensible locations found and frequency of the associated peaks. These data can be used also to produce projections: will be shown in a subsequent dedicated entry.

SDB1 chamber is the location with more associated peaks. Some of these peaks are shared with DET cryotrap, SR, and the minilinks, in particular the most sensitive location turns out to be the B5 minilink viewport.

A few distintive peaks are associated to PR and to SIB1.

Locations that seem essentially immune to tappings are NI, WI, BS, SDB2, SIB2, SPRB.

Figures 1-4 show peaks in hrec excited by tappings in the SDB1_SouthFlange, DT_cryotrap_vessel, SR_EastFlange, PR_NorthFlange, SIB1. Figures 5-9 show excitation recoded by accelerometers on these vacuum chambers.

Figures 10,11 show peaks in hrec excited by tappings on the minilinks and EQB1 chamber. Figures 12-14 show excitations recorded by accelerometers on these vacuum chambers (or closest chambers in the case of minilinks).

ITF found in UPGRADING Mode with INJ not working due to EIB_SBE open, after closing it the IB autoalignment was off, during the throubleshooting INJ has restored its functionality by its own.
All times are UTC.
Activities done or comunicated to the operator:
- 7:10 MAINTENANCE Mode set;
- 7:15 EIB loops closed;
- From 8:10 to 9:52  heavy work on truck doors of CEB (Fabozzi);
- From 8:46 to 8:54 TCS Camera Reference (operator);
- From 9:03 to 9:17 TCS CO2 Power Checks (operator);
- 12:00 Mainteance ended, UPGRADING Mode set with arms locked on the IR with ARMS_LOCK node in LOCKED_ARMS_IR;
- 13:16 Restarted ELE_COB process on VPM;
- 13:28 Shelved DMS flag: Eurotherm_devices ping_COB_Eurotherm under DMS > DAQ-Computing > INF_devices > Eurotherm_devices;
- 13:37 Recenterd DMS flag: ENV..IB_F0_TE2 on VPM under SuspShortMoni configuration;
- 14:38 Shelved DMS flags: NNC_WEB, NNC_NEB, and NNCToDAQ under DMS > VPM > NewtonNoise;
ITF left in UPGRADING with both arms locked on the IR.
At 22:47 I recenterd DMS flag: INF..TCS_PR_CHROCC_TE_IntHeater under DMS > TCS > Chrocc_PR from remote;

TCS CO2 Power Checks (measured at CH Pickoff): 

The aim of this shift is to measure the thermal transient of the NE and WE Ring heater. Previous measurements made during the commissioning of O4 showed a discrepancy between the RH calibration estimated from simulation and the observation [VIR-0739A-23]. Also, previous measurements made during the commissioning break between O4b and O4c showed that the astigmatism has a higher amplitude when the ring heater of the NE mirror was ON [VIR-0562A-25] (no measurement for the West arm has been made due to the change of the WE mirror). The aim of the scans presented here is to redo those measurements. This time, the new results obtained from the thermal transient of the cryotrap [68417] will be taken into account in the derivation of the calibration.

Scans started at 8:49 UTC with the ring heater off for around one hour before the start of the transient. The RHs of the West end and North end mirrors have been turned ON at 10:10UTC and 10:11UTC respectively [68421]. Below is the list of scans done during the shift with their starting and end dates. Between each series, the arms are relocked on IR and green.

UTC time-----------Action                                                          

8:49-9:21 15 iterations of scan using CARM_SET_scan_FSR(numiteration = 15, f_FSR=110000,timescan = 60.)

9:23-9:55 15 iterations of scan using CARM_SET_scan_FSR(numiteration = 15, f_FSR=110000,timescan = 60.)

9:57-10:29 15 iterations of scan using CARM_SET_scan_FSR(numiteration = 15, f_FSR=110000,timescan = 60.)

10:32-11:04 15 iterations of scan using CARM_SET_scan_FSR(numiteration = 15, f_FSR=110000,timescan = 60.)

11:07-11:38 15 iterations of scan using CARM_SET_scan_FSR(numiteration = 15, f_FSR=110000,timescan = 60.)

11:41-12:12 15 iterations of scan using CARM_SET_scan_FSR(numiteration = 15, f_FSR=110000,timescan = 60.)

12:15-12:47 15 iterations of scan using CARM_SET_scan_FSR(numiteration = 15, f_FSR=110000,timescan = 60.)

12:55-13:27 15 iterations of scan using CARM_SET_scan_FSR(numiteration = 15, f_FSR=110000,timescan = 60.)

13:30-14:02 15 iterations of scan using CARM_SET_scan_FSR(numiteration = 15, f_FSR=110000,timescan = 60.)

14:06-14:38 15 iterations of scan using CARM_SET_scan_FSR(numiteration = 15, f_FSR=110000,timescan = 60.)

14:40-15:12 15 iterations of scan using CARM_SET_scan_FSR(numiteration = 15, f_FSR=110000,timescan = 60.)

15:14-15:25 15 iterations of scan using CARM_SET_scan_FSR(numiteration = 15, f_FSR=110000,timescan = 60.) Unlock before the end

15:28-16:00 15 iterations of scan using CARM_SET_scan_FSR(numiteration = 10, f_FSR=110000,timescan = 60.)

Figures 1 and 2 show the evolution of the distance of each mode from the fundamental mode normalized by the FSR during the transient for the West and North cavities. The results form HG04 are constant for the time 11-41UTC, it correspond to the moment where the fourth order mode is at the same position than the sidebands at 56MHz. Further analysis will be done and presented in comment of this logbook including the meausrement of astigmaitsm during the transient and in-situ estimation of the RH calibration.

As agreed, the ETM RHs were configured and switched ON for the arm cavity scan with RH transients.

I set the NE RH to nominal values: 16.6 V (7.4 W).

I set the WE RH to nominal values: 17.4 V (8.14 W).

At 10:10 UTC, the WE RH was switched ON.

At 10:11 UTC, the NE RH was switched ON.

ITF in UPGRADING, state DOWN
8:00 UTC OMI INJ chiller filter changed (De Rossi, Zaza)
8:40 UTC Arm FSR scan of RH transient (Jacquet)
10:00 UTC NE/WE RH switched on at nominal power (Lumaca)

This morning we made the refill of the water in the INJ chillers and changed the filter of the main chiller.

Figure 1. The ring heater temperature gives us with a little more precision the time of the opening of the cryo trap valves. It was between 8:25 UTC and 8:26 UTC.

ITF found in UPGRADING Mode with Arm FSR scan of cryotrap transient commissioning activity ongoing (Cjacquet). Activity concluded at 17:07 UTC. Logbook entry #68417.
Under request of Pasqualetti I added MOBILE3, under Particles, set of flags alarmed in the DMS.
ITF left in UPGRADING Mode with the arms locked in the IR.

This logbook presents the scans made during the thermal transient of the west arm cryotrap. At 8:30 UTC the vavles have been opened (68410). Scans started at 9:29UTC, below is the list of scans done. After each scan the cavity are locked on IR, then on green before the start of the next serie of scans.

Observations during the shift

The first series of scans (from 9:29UTC to 11:06UTC) stopped before the end due to an unlock of the green. In the scan series done until the end between 11:09UTC and 13:50UTC, the first order mode in the west cavity seems to increase a lot over time, suggesting that the cavity was misaligning during the scans. This produced an unexpected result concerning the mode spacing in scan. The resonance position was shifted in the opposite direction compare to the expectation regarding the transient produced by the cryotrap (See figure 1 showing an example for the second order mode). It is possible to remove the divergent points by keeping only the data where P_HG01<0.05mW. This give the figure 2. After 13:53 and until the end of the shift, I stopped manually the scan when the observed amplitude of the HG01 was reaching 0.04mW or more. 

These figures illustrates details of the peaks that are excited during tappings on SDB1 chamber South flange (data of Nov 28, 9:28:50, 120s - purple curve) and during one acoustic injection in CEB (data of Nov 29, 12:19:10, 180s - green curve).

Note that some of the peaks are also present (small) in the quiet hrec.

In the txt file is a list of the center frequency of these peaks. The "*" indicates that the peak is also seen in quiet hrec, "T" if it is excited by tapping SDB1, "A" if it is excited by acoustic noise in CEB.

The conclusion we draw in https://logbook.virgo-gw.eu/virgo/?r=67936 is not correct. Instead, the correct conclusion is that the family of peaks that arise in hrec when injecting acoustic noise in the CEB hall are associated to vibration of SDB1 chamber.

The attached figures show the effect in hrec and noise levels in microphones of CEB hall and inside DT lab (EDB) and vibration of SDB1 chamber during:  one acoustic injection inside the CEB hall (Figure 1), one acoustic injection inside DT lab (Figure 2) and tappings of SDB1 chamber (Figure 3). 

Similar peaks are excited in hrec. Comparing env probes is evident that the driver of the peaks in hrec is the level of vibration of SDB1 chamber.

At NE, on Wednesday 17 December 2025

Worked on the NE Pcal reflection bench, to investigate possible sources of optical losses (expected at the level of <0.9%) from the steering mirror first, and from the viewport then.

• 13:05.00 UTC start activity, open reflection bench cover.
• 13:11.14 -> reduced the angle of incidence of the beam on the steering mirror (and moving the sphere to keep the beam centered)
• 13.15.55 -> put back to initial positions.
• 13:21 -> put back the cover on the bench
• 13:24.10 -> switch off pcal NE lines
• 13.26 -> reopen the bench cover
• 13.29 -> reduced again the aoi, even a bit more than first time (a bit smaller, cannot do more otherwise the input beam is clipped) 
• 13.31.24 -> increased the distance between the sphere and the input beam by ~2 mm (without changing the aoi on the steering mirror, hence beam less well centered on the sphere)
• 13.34.15 -> slightly increased the AOI to center again the beam in the sphere input 
• 13.37.40 -> went back to the initial positions.
• 13.44 -> increased the AOI, moved the sphere by about 2 cm (increasing it distance to the viewport)
• 13.48.45 -> increased the aperture of the diaphragm installed on the viewport.

• 14h25 UTC ->  stop laser, visual inspection of the viewport; presence of scratches at the bottom at least, and of dust.
• 14h30 UTC -> blow viewport with compressed air (during this action, the sphere was not attached on the bench, it may have been moved a bit, even if we do not think so). Note that due to limited access, the air could not be blown from the side of the viewport, but mainly from the front, with a small angle. Also the mount to support the diaphragm may prevent the dust to go away easily when doing this action.
• 14h32 UTC -> switch on laser and loop
• 14h35 UTC -> stop laser
• 14.40 UTC -> cleaned viewport with tissue  (during this action, the sphere was touched, and then recentered on the beam). Again, difficult access, so cleaning doing some rotation movements around the center.
• 14h45 UTC -> switch on laser and loop
• 15h10 UTC -> laser stopped to dismount the sphere and mirror, and bring them back to LAPP.
• 15h15 UTC -> took some pictures (se figures 3 and 4)

The two first figures show the trend of the two photodiodes (Tx_PD2 in loop) and of the sphere during this period.

• there was no significant change of the power measured by the sphere when changing the aoi on the steering mirror.
• after blowing air on the viewport, the power measured by the sphere was reduced by 2% to 3% (...but we have a doubt to have possibly misaligned the sphere when blowing the air without noticing).
• after passing a clean tissue on the viewport, the power measured by the sphere may have increased by about 0.1% (see the last part of the figure 2).
• note that the viewport was not clean even after these actions, as at least dust was still visible and also some thin layer, even if possibly less around the center itself.

Visual inspection of the viewport (also see the pictures 3 and 4): there are scratches at least at the bottom of the viewport, quite some dust. Before cleaning with the tissue,  we could see a layer of something on the viewport, which was less visible around the center after the tentative cleaning. However, the viewport is difficult to access for cleaning, and to observe, because of the supporting structure of the diaphram in front of it. 

In the Rx calibration done for the previous logbook entry, figure 7 is correct for the top plot (Rx / Tx_PD1) but not for the bottom plot (Rx / Tx_PD2): in the analysis code, the correction to be applied to take into account the new calibration of the phototiode was applied only on the Tx_PD1 photodiode, not on the Tx_PD2 one.

The code has been modified to correct for both now. The initial "old gain" of the Rx sphere is the one being set in March 2024. The update figure is given below, and the results summarized in the table:

For NE PCal, the photodiode Tx_PD1 has a slight dependence on humidity, hence the reference calibration used for long term monitoring is based on Tx_PD2, in bold in the table.