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.

ITF found in UPGRADING Mode and North Arm locked.

At around 8:30 UTC the WEST valves have been opened; I manually realigned the cavity and then started the planned activity of arm FSR scan.

Activity still in progress.

WE CALIBRATION ON 2025_12_17
On Wednesday, 17th, we did calibration activities on the WE PCal.
We first performed the installation of WSV at WE at approximately 7h45 UTC, switched off the laser and started the installation of WSV on the reflection bench.

ADC channel calibration
- Calibration for the temperature channel 5 ADC 0 (8h30 UTC)
with a multifunction calibrator Time series connected to the input of the follower circuit for the PCAL_WE_WSV_temp channel. Here the list of actions performed:
         • Changing the channel gain to 200 and offset to 0. in the SWEB_dbox_rack config
         • Signal injection from 0 to -6V with 2V steps with the Time Series
         • Computing the calibration coefficient (gain and offset) with a linear regression
         • updating the coefficient in the config at approximately 8h50  UTC

- Calibration for the power channel ch6 ADC 0 (8h55 UTC):
with a multifunction calibrator Time series connected to the input of the follower circuit for the PCAL_WE_WSV_DC channel. Here the list of the actions performed:

• Changing the channel gain to 2. and offset to 0. in the SNEB_dbox_rack config
• Signal injection from 0 to -6V with 1V steps with the Time Series
• Computing the calibration coefficient (gain and offset) with a linear regression
• updating the coefficient in the config at approximately 9h10 UTC

 
The following table contains the old/new gains and offset for each calibration performed:

See figures 4 & 5 for the linear regression plots (POWER and TEMP)

 
 
WE Tx_PD1/2 vs WSV calibration measurement -

WSV gain used as reference : -2.617869 V/W

• 09:32 UTC -> background measurement (still wait 30’ for stabilization)
• 1450000830.0 (10 UTC) -> START Background measurement
• LASER ON: 11:04 UTC (1450005318) (wait for thermalisation 30 min), until 16h05 UTC

Here is the command used: python3 photodiode_calibration.py 1450007100 16200 1450000830 3600 WE

The following table contains the old/new gains and offset for each photodiode:

WE Rx vs Tx_PD1 and WE Rx vs Tx_PD2 calibrations
Around 16h15 UTC, removed WSV and put back Rx sphere
Background measurement: 16h40 UTC (1450024800), for 2 hours
At 18h37 UTC, laser switched on
Measurement: 1450034000, for ~6h
Command launched: python3 Rx_sphere_calibration.py 1450034000 22000 1450029000 2600 WE
with the following correction coefficients (these coefficients are used in the code to take into account the new Tx_PD calibration gains, but without changing the ADC gains themselves for long term monitoring):
coeff = -0.739903/-0.740169,-0.784602/-0.783431    #new/old Tx_PD1 and Tx_PD2 WE, 2025/12/17
 

(See figures 6&7 for the ratios and background levels)

Two possible results, depending on which photodiode is used as reference (Tx_PD1 used as reference for WE, since PD2 have a sligth dependence with humidity):
 
1/ Rx sphere new gain (w.r.t Tx_PD1): 0.689194 W/V    offset -0.001159 W
correction factors:
    Rx_sphere: 0.997907 +/- 0.000053
 
2/ Rx sphere new gain (w.r.t Tx_PD2): 0.689149 W/V    offset -0.001164 W
correction factors:
    Rx_sphere: 0.997843 +/- 0.000054

 

In the frame of the ALS shift we had to block the beam on the LB in order to block the EIB.

We found that the flip mirror at the output of the PMC is not working, nor from the VPM (TTL_inj process, CH3) or directly pushing the button.

While trying to debug it, the cable of the flip mirror accidentally passed through the beam in front of the input window of the PMC. Of course it got burnt and made some plastic dust. Few seconds later, we observed a decrease of the PMC TRA power by 10% (from 0.8V to 0.72V ). All the missing power seems to be in the order 2 mode, so it seems to be pure mismatch (plot 1).

The IMC TRA power has been adjusted to 18W by the Automation with the IPC1. We compared the spectra of the different inj loops before and after the accident (plot 2), and since there are no major differences we decided to keep everything like this and monitor the transmission of the PMC in the next days. 

This morning we wanted to make a characterization of the green beam coming from the north arm (the west being unavailable).

We blocked the EIB and relocked INJ, the north arm and ALS in reflection, but the IMC started to be very unstable and unlocking (we had to manually realign the bench and the mc mirror, but it kept unlocking).

We then decided to reverse all the operations and relock the injection in a stable way.

After speaking with Paolo we found out that a possibility could be to switch back to the old bpc alignment strategy (by setting to 0 IMC_ON in the BPC DSP card) when the EIB is blocked, in which the references are only the quadrants on the EIB (while now the beam follows SIB1 in tz and ty once the IMC is locked).

ITF found in UPGRADING Mode and North Arm locked.

At around 10:30 UTC Camilla and Mathieu started to work in laser lab; activity concluded at around 13:00 UTC.

Yesterday afternoon, we have dismounted the NE_Rx sphere of the NE PCal, to bring it back to LAPP for extra-noise investigation. We also took the steering mirror to check its reflection vs aoi at LAPP.

We put a beam dump on the bench, see picture.

We also stopped the PCal laser. The laser driver is still on, but the pump diode is switched off.

ITF found in UPGRADING Mode and North Arm locked. I found SIB2_SBE, FCIM_SBE, and MC_MAR_Z_ON loops open.
At 06:59 UTC I closed SIB2_SBE.
At 07:01 UTC I closed FCIM_SBE.
From 8:21 to 9:08 UTC De Laurentis and Gargiulo went in DET Lab for wafers replacement.
At 10:46 UTC MC_MAR_Z_ON loop closed by Ruggi.
From 13:30 UTC Tringali went to WEB to disconnect microphones of newtonian array.

The power supply Hameg29 network interface was configured in USB. We have configured it in DHCP around 14h00 UTC, and it was then available from the remote control process PCal_PowerSupply.

Yesterday we did calibration activities on the NE PCal.

We first performed the installation of WSV at NE at approximately 8h UTC, switched off the laser and started the installation of WSV on the reflection bench.

ADC channel calibration NE:
- Calibration for the temperature channel 5 ADC 0 (10h10 UTC):
with a multifunction calibrator Time series connected to the input of the follower circuit for the PCAL_NE_WSV_temp channel. Here the list of actions performed:
• Changing the channel gain to 200 and offset to 0. in the SNEB_dbox_rack config
• Signal injection from 0 to -6V with 2V steps with the Time Series
• Computing the calibration coefficient (gain and offset) with a linear regression
• updating the coefficient in the config at approximately 10h30  UTC

- Calibration for the power channel ch6 ADC 0 (10h40 UTC):
with a multifunction calibrator Time series connected to the input of the follower circuit for the PCAL_NE_WSV_DC channel. Here the list of the actions performed:

• Changing the channel gain to 2. and offset to 0. in the SNEB_dbox_rack config

• Signal injection from 0 to -6V with 1V steps with the Time Series

• Computing the calibration coefficient (gain and offset) with a linear regression

• updating the coefficient in the config at approximately 12h00 UTC

You will find attached the linear regression associated to both the temperature and power calibration (see figure 1&2).
Here is the tab summaring the old&new values of the gain and offset:

NE Tx_PD1/2 calibration vs WSV measurement 

• Start of background measurement : 11h30 (UTC) for 1h

• Laser turned on at 1.3W : 13h30 UTC

We will have a first glance at the data around 16h00 UTC to see the quality of this latter. We checked the results at about 16h15 UTC and the values were consistent with what was expected (data were stable all along the measurements), we thus interrupted the measurement and run the analysis scripts from which we extracted the following gains/offsets (see figures 3,4,5)

Here is the command used: python3 photodiode_calibration.py 1449930618 5400 1449919818 3600 NE

NE Rx calibration vs Tx_PD1 photodiode

BACKGROUND START 18 UTC (for 1 hour) (see figure 6)

LASER ON 20.50 

MEASUREMENT START AT 22 UTC (for 8 hours) (see figure 7 for the ratio measurements)

Here is the command used:  python3 Rx_sphere_calibration.py 1449957618 28800 1449943218 3600 NE

(using Tx_PD1 as reference is hard-coded)

Finally, the analysis results are as follows:

• Rx sphere new gain : 0.729448, new offset : -0.002623 (using Tx_PD1)
• Rx sphere old gain :  0.730861 , old offset : -0.002632

On the ADC configuration, we updated only the ADC voltage calibration used for the two WSV channels (temperature and power), but we did not update any gains nor offsets for the Tx_PD1,PD2 or Rx photodiodes: all the values are still as they were during O4, since March 2024.

Figure 1. After 17 hours the temperature transient is still ongoing, this means that there is no point in closing the north arm cryotrap valves on Thursday evening, as the north arm will not have the time to arrive at a steady state my Friday morning. The temperature change is more than one degree Kelvin, this should allow for an estimation of the cooling power the cryotrap. For example assuming that the mirrors are perfect black bodies (which they probably are not so it is an approximation) the power needed to change the temperature by 1.5 degrees is 3.4 Watts.