The aim of this shift, and the subsequent ones, is to perform the fine alignment of the WI PAM and characterize it using HWS-INJ.

Last Friday, I noticed that both TCS_PAM_WI_PowerSupply and TCS_PAM_WI_pico processes were grey in the VPM. I attempted to restart them, but without success. I then asked Giulio to check the devices, and he confirmed that neither the pico driver (picocltcs2) nor the power supply (rstcs3) was responding to ping requests.

This morning, Giulio restarted the WI pico driver and pico server, restoring communication with the devices (see 69946).

After lunch, we went to the TCS room to restart the WI PAM power supply process. 

Since the WI mirror will be repeatedly heated during the PAM tests, the etalon control loop was switched off at 12:34 UTC by Madda and Francesco.

For the HWS-INJ measurement, I retrieved the positions of the optical components along the beam path used during the CO₂ actuator centering on the West CP (see 69694). The goal is to reproduce the same optical configuration, for which the position of the WI mirror center on the HWS-INJ wavefront maps has already been determined. The corresponding reference measurement was performed on September 4, 2026, between 17:19 and 17:35 UTC. The data are stored in folder 20260904T1919 (see Fig. 1).However, Francesco noticed that the current alignment differed significantly from that of September 4. Therefore, I decided to repeat the HWS-INJ measurement by switching on the CH to determine the current position of the WI mirror center on the HWS-INJ map.

% CH switching ON
I switched ON the HWS-INJ SLED at 1.42 V
ITF in WI SINGLE BOUNCE +PR aligned 
13.29 UTC: HWS-INJ START (20261019T1529)
13.35 UTC: CH ON at high power (WF 8)
13.48 UTC: CH OFF (WF 33 ) and HWS acquisition stopped

The CH appeared clearly in the HWS map (see fig.2).
%%%%%%%%%%
Then, I took advantage of the thermal transient to go to the TCS room and switch off the lasers (69955). 
%%%%%%%%%%

% WI PAM switching ON

The first measurement with the WI PAM was performed with the beam in free propagation, without any mask installed.
The voltage applied to the source was gradually increased using voltage ramps lasting several hundred seconds.

Data acquisition started at 14:57 UTC (20261019T1657). At approximately 5 V (T ≈ 430 °C), the OPL induced by the PAM became visible in the HWS maps only after piston and tilt removal (Fig. 3).

At 6.5 V (T ≈ 620 °C), the PAM-induced OPL was clearly visible in the HWS maps even without removing piston and tilt (Fig. 4).

At the end of the shift (20:00 LT), I switched off the actuator. Tomorrow, we will proceed with further characterization measurements.
I left the ITF in WI single bounce+ PR aligned.

This afternoon, between 14:00 and 14:30 UTC, all CO₂ lasers (Main and CH) and their chillers were switched off in preparation for the electrical work scheduled for tomorrow morning in the TCS chiller room (Fig. 2).

The chillers and the microphone were also covered with protective sheets to prevent dust accumulation.

This morning we did some tests to try to understand the excess of noise
Here are the GPS :

09:38 UTC - INJ AA loop open (from DSP card)
09: 59 UTC - IMC unlock (from VPM)
13:18 UTC - PSTAB open

Surprisingly the cycle IMC unlocked / locked arounf 10 am made the noise as seen on RFC_8MHz disappear. This might go in favour of some saturation in the frequency loop actuators. 
However, I checked some IMC unlocks of the previous days and the noise was present both before and after the unlock. 
I checked if there was other changes in the INJ parameters but could not spot anything obvious. 

ITF found in locked arms IR.

Below the activities communicated in control room:

• SR electrical check (Fabio);
• HYMO maintenace at WEB/MCB;
• from 8:30 UTC noise injections on the suspesions with ITF unlocked (Manuel and Paolo);
• from 12:00 UTC PAM pre-commissioning (Ilaria) with the ITF in WI single bounce with PR aligned. Activity in progress at the end of the shift.

SBE

SIB2 and SPRB vertical position recovered with stepper motors; loops properly closed.

LSC

at 12:34 UTC WI etalon disabled under request of Maddalena.

Since the access to SR tower is over, today at 10:15 UTC I removed the beam dumps from EQB1.

To prevent any unintentional change to the CO2 configuration, I put in PAUSE the TCS_MAIN node; ITF_LOCK is already paused and should not be revived before we start relocking on Thursday afternoon.

Laser frequency noise has been a major limitations during these measurements, making any conclusions on the effect on the BNS range in general, or on the HOM noise (mystery noise) difficult to make. The higher laser frequency noise is due to something that happened on Oct 7 around 19:00 UTC and above 300Hz due to the more noisy LNFS: https://logbook.virgo-gw.eu/virgo/?r=69929.

Figure 1 shows a noise budget in the starting tuned SR configuration. The fitted HOM noise level is comparable to the case of January, when the first stage of SR diaphragm was already installed, for the times when the etalon effect was making the B1p higher. It is unclear in what position the etalon effect was on Oct 14. The estimated frequency noise contribution is comparable to the HOM noise, so the fitted level of HOM noise depends strongly on whether that frequency noise estimation is correct or not.

Figure 2 shows the SR detuned configuration. The frequency noise estimation decreases, because the coupling was lower by a factor ~2 in detuned SR. The estimated HOM noise also decreases by about 20%, which is less of decrease than what was measured in March with the SR diaphragm. It is hard to draw a conclusion from that, as it may be due to many reasons. A tentative conclusion is that the SR detuning is not dramatically better at reducing the HOM noise without the SR diaphragm. At low frequency the sensitivity is much worse, because this data is in LN2 (with many dither lines on), unlike the figure 1 in LN3. 

The 2026-10-18 I found  some SBE SPRB DMS flags red with the follozing comment : SBE_SPRB_ACT_F0H0_raw loops ringing . The SBE SPRB controls was in this state  since the 2026-10-17-08h00-UTC 

I made some actions trying to recover the correct running conditions but without success : 

• actions performed between  the 2026-10-18-06h25m05-UTC and 2026-10-18-06h35m33-UTC

At the end the SBE SPRB loops were left open 

In preparation for the HWS-INJ measurements with the WI PAM, I blocked all CO₂ beams (DAS and CH) on the bench.

• 2026-10-19 08h06m03 UTC    ilaria 'WI_Bench:OUT UP [byte=2]' sent to TTL_co2
• 2026-10-19 08h06m04 UTC    ilaria 'WI_Bench:CH UP [byte=3]' sent to TTL_co2

This morning at 9.45 LC, I restarted the Pico driver (picocltcs2), which was running but was not responding to ping...
I then successfully restarted the TCS_PAM_WI_Pico server via VPM.

14:00 ITF found in DOWN state UPGRADING mode

15:30 UTC SR tower baffle installation completed (#69941), start of vacuum pumping

ITF left in DOWN state and UPGRADING mode

here the BruCo using as target LSC_PRCL: https://scientists.virgo-gw.eu/DataAnalysis/DetCharDev/users/fiori/bruco/LSC_PRCL_1475998223/bruco.html

ITF found in UPGRADING mode and DOWN state.
All times are UTC.
07:40 Permit to work inside SR tower open (Galimberti, #69937). Flange open shortly after (VAC, #69938).
08:35 SR diaphragm installation begin (Majorana, Pinto). Still ongoing at 14:35.

ITF left in UPGRADING mode and LOCKED_ARMS_IR_ALS requested by ARMS_LOCK metatron node.

We run a BruCo, coherences are computed up to 1kHz:
https://scientists.virgo-gw.eu/DataAnalysis/DetCharDev/users/fiori/bruco/Hrec_hoft_1475998223/bruco.html

The pole at 500Hz noise that appeared on Oct 7 around 19:00 UTC is also visible in other channels earlier in the INJ chain.

Figure 1 and 2 compare the time before the issue started (purple) with a time after (blue) respectively on Oct 8 and Oct 14. All the times are with the interferometer in LN2 or LN3. The additional noise is visible clearly also on the Audio band monitoring of the EOM transmission, on the EOM correction, and much less clearly on the PMC transmission.

If the extra noise is visible on the EOM transmission (INJ_EAB_EOM_TRA_AUDIO) both with the IMC locked and unlocked, then it should make it easier to find. As the IMC can be excluded from the investigation, but most likely the problem becomes invisible in that case, as the laser amplitude noise will dominate everything with the PSTAB loop open.

We restarted the recovery of the system.

The CC PLL was already locked, the first things was checked was the relock of the squeezer. The level of the green was too low and the contrast of the MZ interferometer was too low. As first thing Fiodor realigned the MZ and we managed to relock it with offset of +0.03V

After that we managed to lock the OPA.

Jean Pierre and Marco recovered the other two PLLs in DETeroom. Note that for the third time we found the SC laser off it switched off by itself without any clear reason.

Finally we restarted to recover the alignment of the squeezer:

1) We locked the CC and we closed the AA. The magnitude was too low

2) We checked SQB1 HWP2 (looking the level of the 4 MHz mag in ASQZ) and HWP1 (minimizing the stay light bump on HD DIFF Audio

3) We checked the alignment of EQB1 PDs

4) We realized that we were clipping on the retroreflector Y because in february we moved downwards the vertical position of SQB1 bench. 

After the realignment we managed to measure:

• 2.29 of parametric gain, i.e. 8.7 dB of generated squeezing
• 8.4 dB of ASQZ phase 1.15 rad
• 5.7 dB of SQZ phase 2.45 rad

we run a phase scan @14:28 UTC but for some reason we found lower level of SQZ and ASQZ. We wanted to redo it but there were some unknow noise probably due to the venting and we could not repeated it.

We decided to move to the delay line. We did not find any light so we asked Fiodor to check in DET lab. And we realized that for safety reason, this summer we closed the GR shutter and we never noticed that when it was closed it clips the beam into the delay line

Once recovered the delay line and aligned with EQB1 Thorlabs picomotors we obtained:

• generated squeezing 8.5 dB
• SQZ level 6.25dB
• ASQZ level 8.2dB
• Phase scan at 16:59:50

The results of the two fits is in the attached figure.

Losses with delay line 9% and phase noise 60mrad. Phase noise better than in february, losses sligthly higher. The additional HWP in the HD path is still rotated for RR so this can cause additional losses

At the end of the shift we lef the RR on, HWP2 of SQB1 rotated toward HD detector, SC, LO shutter closed and MCIR unlocked

ITF found DOWN in COMMISSIONING mode with SR, SDB2, SDB1 loops opened.
UPGRADING mode set.
- INJ_MAIN, ARMS_LOCK, DRMI_LOCK, OMC_LOCK Metatron nodes set in manual.
- DRMI_LOCK, SUS_PR, SUS_SR Metatron node set in pause. ITF_LOCK, DET_MAIN already in pause.
- SR venting in progress
- planned activity: Squeezing beam blocked towards SDB1 (Sorrentino) 

SBE
18:20 UTC - SPRB vertical position recovered via stepping motors.

Today around 16:10 UTC I put three beam dumps on EQB1 in front of the windows towards SQB1 for laser safety in view of SR tower access. 

Figure 1. Comparing the spectrum of yesterday to the beginning of the year, the noise level of SRCL, PRCL, MICH is a factor few higher than before. Especially on PRCL. This is also the case of noise on the SSFS quadrature. 

The question is what it is and where it comes from. The noise is likely to be present on the laser frequency, and then polluting all LSC channels. It may be related to the higher noise level of the LNFS.

Figure 2 The more structured noise that is visible in SRCL between 300Hz and 3kHz is very coherent with the excess noise in the LNFS. So that part is clearly due to the more noisy LNFS. For the excess noise in PRCL, and the excess noise in SRCL below 300Hz it is less plausiable. As there is no coherence with the LNFS phase noise, and the LNFS broaband noise below 300Hz is the same as it was at the beginning of the year.

Figure 3 shows yesterday in purple, Friday last week in red, and the beginning of the year in blue. Some version of the pole at 500Hz noise is back, it is clearly visible on SIB2 RFC 8MHz I, the level doesn't appear to be stable as it is different on Friday last week and yesterday, and the changes in noise level of PRCL and SSFS quadrature are correlated with those pole at 500Hz noise changes visible on RFC 8MHz I. 

Figure 4 Looking at data of various nights with arms locked, the pole at 500Hz noise seems to have appeared on October 7. It would be important to look at that more precisely to see at what time the extra noise appeared. One hardware activity on that day was the realignment of the phase camera, and maybe a change in the splitters for the local oscillator of the phase camera https://logbook.virgo-gw.eu/virgo/?r=69877

Figure 5. Searching more precisely it looks like the problem started around 19:00 UTC, there was an interferometer unlock from LN2 at that time.

WIth the SR tower under venting, we setup the automation in the following way:

• DET_MAIN in SHUTTER_CLOSED, then paused;
• SUS_PR in MISALIGNED, then paused;
• SUS_SR in MISALIGNED, then paused;
• DRMI_LOCK in MISALIGNED_PR_SR, then paused;
• ITF_LOCK in DOWN, then paused;
• OMC_LOCK in TEMP_CONTROLLED, then manual;
• INJ_MAIN in IMC_RESTORED, then manual;
• ARMS_LOCK in LOCKED_ARMS_IR, then manual;
• all other nodes unchanged.

ITF found in locked arms ir.

At 7:00 UTC started the planned SR venitng; operations performed:

• SR suspension loops opened
• DET main in pause in SHUTTER_CLOSED; 
• SDB2_SBE, SDB2_LC, SDB1_LC opened.

In parallel other two activities were carried out:

• squeezing recovery in standalone; still in progress.
• arm astigmatism measuremet; completed.

HVAC

Under request of Davide:

• I enabled the PyHVAC INJ servo at from 7:56 UTC to 8:53 UTC;
• at 12:21 UTC I switched off the PyHVAC server.