This night the ITF unlocked at 1:12UTC and the automation did't try to relock and in some way set the ITF_LOCK node request to DOWN the relock has been resumed by Michal, it happened again after the first unlock from LOW_NOISE_3 of the morning (10:19UTC); during the day Michal worked on beam spot position on WE with the ITF locked at CARM_NULL_1F and LOW_NOISE_3 state (#66626), this activity stopped at around 14:00UTC; then the ITF was locked at LOW_NOISE_3, calibration from 14:57UTC to 15:15UTC; I left the ITF locked at LOW_NOISE_3 with the failsafe engaged (DQ_STUDIES).

Calibration
- 14:58UTC: Measurement of actuators response for NE,WE actuators and NI,WI,BS marionettes (CALIBRATED_DF_PCAL);

Strangely enough, there seems to be a second glitch before (or after) the 25-min glitch which appears more often compared to before the WE mirror replacement.
Fig. 1 shows the spectrogram of Hrec_hoft_20000Hz for 15000 s with 10s time steps from 05-03-2025 at 21:00 UTC, fig. 2 shows a close-up on the first 1.2 hours with 3 glitches.

Fig. 3 shows the same spectrogram but from yesterday 24-04-2025 at 21:00 UTC, fig. 4 shows the close-up at the last 1.2 hours with 3 glitches.

The time difference between the 2 glitches is not constant and is the order of 1 minute.

The interferometer unlocked during the night, and did not try relocking. There might be an issue with the automation of the autorelock.

After the recovery the power in the arms has been lower by about 10% and the DARM optical gain worse by 20% than before the WE mirror swap. This made the sensitivity much worse.

Figure 1 shows an exporation of the beam spot position on WE done in CARM NULL 1F between 6:30 UTC and 8:30 UTC, using instruction listed in https://git.ligo.org/virgo/commissioning/commissioning-tasks/-/issues/68 applied to WE. In horizontal direction there was not a significant change, but in the vertical one there was a clear improvement in the carrier recycling power (higher power on B4). A 6mm vertical displacement increased the power by ~10%, back to similar values that we had before the WE replacement.

With the old WE mirror, the issue was mainly in the horizontal direction, with the losses depending on the horizontal position on the WE. So this has clearly changed. The dependence looks higher, meaning the point absorber on the new WE mirror is either bigger, or closer to the center of the mirror.

Figure 2. Once in LN3 the change in spot position has also improved the DARM optical gain by ~20%, restoring it to a value similar to what it was at the beginning of April.

Figure 3. However the offset on WE mirror position creates a very clear coupling with DIFFp_TX, with coherence up to 80%

Figure 4 shows the WE mirror before moving the beam and Figure 5 after moving the beam. Displacing the beam reduces the power on the two markes on the baffle, but it also reveals more a ring like structure at the top of the mirror, which is a few cm from the edge of the mirror. Looking at pictures from the installation that ring like feature corresponds roughly to were the edge of the first contact coating was on the front side of the mirror  https://logbook.virgo-gw.eu/virgo/?r=66548 It is noticeable, but not brighter than the point defects on that part of the mirror.

Figure 6. I have then made a couple of attempts of adding also a vertical offset on NE to reduce the DIFFp coupling. This was not successful. In retrospect, it is  because the DIFFp correction is applied to only one mirror: WE. And the COMMp correction are applied to NE, instead of having a real differential and common angular driving. Hence adding an offset to NE doesn't change the DIFFp coupling, it just adds some COMMp coupling. The COMMp correction are about a factor 10 smaller than the DIFFp correction above 10Hz, hence if an offset on WE is needed, swapping which end mirror is used for which degree of freedom would reduce the impact of a WE mirror offset by a factor ~10.

Figure 7 compares data with the WE vertical offset (purple) and data during the night without (blue). The offset improves the sensitivity above 100Hz due to the better sensing noise (higher DARM gain), but spoils it below 50Hz due to the additional DIFFp TX coupling.

Not that there was much hope they would go away with the NE replacement, but that plot for instance clearly shows that the 25-minute glitches are still there.

The parameters of Online BruCo have been changed so that it should now run automatically on segments in LOW_NOISE_3 (instead of SCIENCE), regardless of whether the AUTORELOCK mode is enabled or not (default setting during data taking). I'll try and revert those temporary changes when we are back in / close to O4c -- they have been documented in that gitlab issue.

Reposting entry from yesterday

Figure 1 shows a scan of the EDB OMC in LN3, the peak with 0.5mW of power just before 12h55 is the carrier order 2 mode if counted the peaks of carrier and sidebands correctly while looking at the scan.

13:06 UTC (20min) EDB OMC is locked on the order 2 mode

Figure 2 shows the spectrum of the order 2 mode. It is dominated by the beam jitter bumps between 200Hz and 600Hz, the laser frequency lines at 227Hz, 1111Hz and 3345Hz are also clearly visible.

I then tried to realign better the OMC using one of the 56MHz sidebands. This was a mistake as the sidebands have a high content of order 1 mode when SR is misaligned (in LN3). As seen comparing past OMC scan with SR aligned and misaligned  https://logbook.virgo-gw.eu/virgo/?r=65260

The EDB OMC will need realigning. Maybe realigning it on the sideband with the interferometer in LN2 will give a reasonable result. And trying to maximize the DARM line with the interferometer in CARM NULL 1F with a DARM offset (but for the DARM line would need to be added to the inputs of the EDB Acl process).

At the next relocked locked again on the order 2 mode and adjusted the alignment to reduce the beam jitter coupling.

17:45 UTC (1h) EDB OMC locked on order 2 mode

Figure 3 shows the shape of the mode, note that the OMC is slightly astigmatic so the horizontal and vertical mode are separated.

Figure 4 compare the transmission spectrum earlier today, and after alignment adjustement to reduce the beam jitter coupling, the bumps are clearly lower by a factor ~10.

While looking at the different modes to arrive to the order 2 mode, the order 1 mode of the carrier looked suspiciously steady. Normally in CARM NULL 1F it fluctuates quickly around zero. Maybe it is the effect of the BS TY loop offset, or some dither lines that are present in CARM NULL 1F being off in LN3.

Putting back the EDB OMC to the parking temperature (below the carrier TEM00).

There is a mistake in the reference picture for the WE camera. As correctly pointed out by Michal, the reported picture of the WE pay cam refers to a time when the integration time of the camera was already decreased down to 450us (from the original 1800us). The correct picture is attached here, along with the circulating power comparison.

I took also a comparison of the illumination of the markers as seen from the camera (second picture: purple is the reference before WE intervention - Apr 3 15:30 UTC, blue is after the intervention). I tried to get a zero reference (third picture) which gives WE_MIR_DR_0 = 26500 a.u., and WE_MIR_UR_0 = 17800 a.u.. This yelds a variation: WE_MIR_DR_2 = 30500 - 26500 = 4000; WE_MIR_UR_2 = 20700 - 17800 = 2700 (after intervention) while WE_MIR_DR_1 =37300 - 26500 = 10800; WE_MIR_UR_1 = 21700 - 17800 = 3900 (before intervention). When accounting for the difference of circulating power in the west arm we have:

WE_DR2 = WE_MIR_DR_2/WE_pwr2 = 8.8; WE_UR2 = WE_MIR_UR_2/WE_pwr2 = 5.9;
WE_DR1 = WE_MIR_DR_1/WE_pwr1 = 22.2; WE_UR1 = WE_MIR_UR_1/WE_pwr1 = 8.0;

The conclusions are that the intervention on the WE payload (mirror + baffle replacement) have for sure removed the bright spot on the bottom left (possibly a spurious reflection of the viewport illuminated by a lot of stray light) and also some reduction on the illumination of the markers of the baffles (to be reassessed after the tuning of the RH is complete).

As a side note, the powers in the arms appear to be more unbalanced than before, but I guess that this also has to be reassessed after the work of recovery is complete.

(I attach here also the picture of the camera after the intervention for completeness, fourth picture).

ITF found in LOW_NOISE_3 in UPGRADING mode. According with commissioners, at 13:34 UTC, I set COMMISSIONING mode.

ITF and TCS tuning activities carried out by commissioning team, Nardecchia and Was from remote concluded at 18:00 UTC with ITF locked at CARM_NULL_1F and LOW_NOISE_2.
At 19:37 UTC ITF unlockd (TBC). Autorelocked at 1st attempt.
ITF left in LN3 (AUTORELOCK_FAILSAFE ACTIVATED).

Today at 14:33 UTC I re-enabled the DOWN condition for the two Etalon loops, now that we have the main beam back most of the time:

• 2025-04-24 16h33m30 UTC AcRelayChTransCmSet> NI_DOWN_OFFSET_trig ask to be set to -2 by ISC_shell_bersanet_farmn5_20250424_092727
• 2025-04-24 16h33m30 UTC AcRelayChTranSet> NI_DOWN_OFFSET_trig, Automatic mode set
• 2025-04-24 16h33m34 UTC AcRelayChTransCmSet> WI_DOWN_OFFSET_trig ask to be set to -2 by ISC_shell_bersanet_farmn5_20250424_092727
• 2025-04-24 16h33m34 UTC AcRelayChTranSet> WI_DOWN_OFFSET_trig, Automatic mode set

After the WE PCal laser was turned back on yesterday we saw an increase in the noise seen by the two photodiode and the Rx sphere (see this plot). 
It appears that this increase in noise is coming from glitches that can be seen in this plot.

Yesterday afternoon I tried turning off the pump diode and turning back on the laser and saw that without the laser control loop we do not see those glitches and that right after truning the pump diode off and back on the glitches did not appear right away but only after a few minutes.
We are not sure what is causing this noise increase at the moment but it is still below the noise requirement. We decided to turn back on the permanent lines around 12h50UTC today on both NE and WE and now the noise seem to have come back to a normal level with the lines (see this plot).

In order to understand the origin of the new noises seen on hrec after recovery, this afternoon at around 14:10 UTC, we unplugged the power PDU of the instrumented Baffle WiFi (see figures).

As agreed during the daily meeting, a new step for the WE RH power was performed in CARM NULL 1F:

STEP 6 – 14:57 UTC (20 minutes after reaching CARM null 1F):
The WE RH power was further decreased to 8.0 W (V = 17.25 V).
(P = 8.2 W (17.5 V) → 8.0 W (17.25 V))

This morning we encountered few unlocks during LN3 due to small glitches in the BS TX optical levers that would cause a saturation of teh B1 photodiode and a consequent loss of control. IN order to overcome this problem we engaged the BS TX in full bandwidth already in LN2, and this time we managed to reach LN3. We automated the engagemenet of the full bandwidth in LN2 again.

The intervention to replace the WE mirror and the replacement of the uncoated payload baffles with the nominal AR-coated baffles has had an improvement on the stray light we can spot with the tower camera.

In the first picture, the situation just before the intervention, with the WE showing some additional brigth spots with respect to the NE.

In the second picture, taken after the recovery of the ITF up to CARM_NULL, the images from the two payload look much more similar to each other (with comparable circulating power situation, see third picture).

A more quantitative analysis could probably be done by adjusting the integration time of the cameras so to avoid saturation, to be possibly scheduled.

It can also be seen that, despite the disappearance of the bright spot on the bottom left of the image of the WE, the markers on the WE payload still look brighter than the equivalent on the NE (and also brighter than before!). It could be useful to swap the cameras to check whether it is related to some differences in the senstivity or it is a true effect of some larger scattering off the NI mirror wrt the WI for instance. To be also re-assessed after the tuning of the ring heaters is complete.

Starting from the status left yesterday evening it was enough to:

• connect to the  phasecam1 machine and restore the /dev/bus/usb permission (reset after any usb port reconnection)  via "sudo service permittyS restart"
• restart the SDB1_Rot server on VPM

After that we could drive everything from the automation and pass succesfully the OMC driving states

ITF found in LOCKED_ARMS_IR and Upgrading mode. The first part of the shift was dedicated to the recovery up to CARM_NULL_1F, with ALS verified by the experts at 13:17 UTC and LOCKED_ARMS_BEAT_DRMI_3F reached at 13:39 UTC after a brief alignment of the PR and SR Mirrors. CARM_NULL_1F reached at the first attempt at 13:44 UTC.
Due to the high power in B1p_DC, at 14:00 UTC under request of the crew I contacted Nardecchia to adjust the power of the Ring Heater.
At 19:27 UTC an attempt to lock the OMC was performed, but ITF_LOCK got stuck in SHUTTER_OPENING. While investigating the problem, Was noticed that there were an issue with the process SDB1_Rot, and the related device connected (see report #66613). I went to the Central Building to disconnect and reconnect the unit, and replace it with a spare one, but it was not possible to restore the standard condition. Further investigation will be performed tomorrow.
ITF left in CARM_NULL_1F.

The slow shutter of the OMC was not opening. There was an error message from the SDB1_Rot process

2025-04-23-19h32m26-UTC>WARNING-error while moving to limit channel 2 axis 1 mode 3

Running the commands by hand did not work either, and after starting the process it didn't not want to restart.

On the computer it is connected to, phasecam1, the device shows on lsusb -v with the following error:

Bus 003 Device 024: ID 104d:3000 Newport Corporation 
Couldn't open device, some information will be missing

The other driver connected to the same computer (the other device is used for squeezing), doesn't not show this error.

Disconnecting and reconnecting the USB cable of the Agilis driver (AG-UC8) did not solve the issue. Disconnecting and connecting the USB bridge it is connected to did not solve the issue. Plugging a spare AG-UC8 did not solve the issue. None of the USB cables connected to phasecam1 looked loose when touching.

To be done is to replace the USB bridge by a spare, and try other ways of understanding why the USB communication doesn't work properly. The device does disappear from the lsusb list when disconnected, and reappears after connecting.

The tuning of the WE RH mentioned in entry 66610 is detailed below. 
Before starting, the B1p value was 0.04 mW.

STEP 1 – 14:16 UTC:
The WE RH power was increased by 200 mW:
P = 7 W (V = 16.1 V) → 7.2 W (V = 16.34 V)

STEP 2 – 14:47 UTC:
The WE RH power was further increased to 8.7 W (V = 18 V).

STEP 3 – 15:30 UTC:
The WE RH power was increased again to 10 W (V = 19.3 V).
After reaching the minimum (about 0.022 mW), B1p started to increase again, returning to the initial value, even surpassing the initial 0.04 mW.
Thus, I performed a final adjustment in the opposite direction.

STEP 5 – 16:58 UTC:
The WE RH power was decreased to 8.2 W (V = 17.5 V)

Following this step, the fringe became darker, reaching 0.03 mW (but the transient is still ongoing).
I left this power for the night. 

The behaviour of the main signals during the RH steps is shown in the attached figure. 

Starting from Tuesday 22 afternoon, after the valve was open again, we started the recovery of the interferometer.

The first, very long step was to find again the West arm alignment and, then, signals on the B8 photodiodes. We could find rather easily the beam on the WE markers by changing orientation of the BS, so to have a rough alignment, then we used the locked North Arm to get a reasonable orientation of the WI by superposition on the B1p camera. However, after all this we could not find signals on B8 even scanning the WE orientation with the "snail".

We also used the reflection of the ALS beam back on the bench, and the spot on the WI mirror in order to improve such alignment.

This morning we changed strategy and we only aligned the West Arm, in order to see the flashes in reflection on the B4 PD up to a similar level to what only the North Arm aligned could provide.

While doing all of the above, we tried to follow with the SWEB alignment (and the vertical position of WE, this one with no effect), which could lead to marginal but visible improvements.

Later, we tried, after we were sure to have the cavity well aligned by hand, to make a "snail" on the SWEB bench itself; this did not work as expected, but a wide change in its orientation actually helped to find again good signals on the bench, which had a very different working point with respect to before. We've been probably chasing a ghost beam before.

We could then recover the lock of the West Arm, which went quite smooth:

• in order to do that, we already made a change in LSC_Acl yesterday, in order to rescale all the B8 signals given the specifications of the new WE mirror (3 ppm of transmission instead of 4 ppm). Mimicking the configuration of the NE (which changed in the same way at the end of 2023), we used a gain of 1.27. After the initial lock of the single West Arm (with a cold ITF and thermal actuators still to be tuned), this seems a bit overestimated, and 1.23 a better value for it. But we will need a more precise measurement in higher configurations;
• once the lock of the arm was engaged, the drift control of the SWEB bench moved considerably its alignment, so we waited a lot in LOCKED_ARMS_IR to have both the benches and the arms' dithering loop to converge; the new setpoints for SWEB have been saved, the configuration not reloaded;
• we recovered most of the Automation by reverting all the changes reported in entry 66517, with the exception of the ITF_STATUS and ITF_CONDITIONS nodes.

Then we moved on with the lock acquisition, getting up to the lock of the DRMI without any problems. We will have to check later if the working point of the West ALS is the best one, but we could lock easily and keep the lock. Once we locked the DRMI, we checked also the SDB1 alignment and we re-engaged the floating setpoints.

We could go then towards CARM_NULL_1F without the need of any adjustment. Once there, after an initial thermalization, we noticed the B1p_DC fringe signal being twice as usual; therefore we started the tuning of the WE Ring Heater, in order to at least reduce the fringe up to a reasonable level before opening of the SDB1 shutter.

We are currently in the RH transient, we'll monitor the situation for the next hours and decide when to do the next step of the recovery.

This morning the work to find the west arm alignment went on; at around 10:00UTC a 6.2 magnitude earthquake in Turkey prevented to go on with the activity during the lunch time; in the afternoon the west cavity was aligned and locked, the lock recovery will go on in the afternoon.

SBE
SIB2, SDB2, SPRB, SNEB and SWEB position controls opened because of the earthquake, controls properly closed.

Figure 1 The beam arrived several times during the snail on the markers of the WI mirror, with spikes of power on the areas of the markers (looking at the video images of the camera it is clear that these are the markers)

Figure 2 Zooms in a few of the peaks. The right areas seems to be for WE TY at around 0, and WE TX at around 150

ITF found in Down State and Upgrading Mode, North Arm Cavity locked.
The shift was dedicated to the recovery of the West Arm cavitiy after the WE intervention, carried out by Casanueva, Bersanetti, De Rossi, Boldrini with the remote support of Was.
After various attempts to realign the cavity, from around 21:15 UTC I started to use the WE Snail to see flashes on B8. I have left it running until 21:15 UTC, but unfortunately I wasn't able to spot any flashes  on the photodiode. After stopping the movements, I returned WE MAR TX and TY to its initial starting point for the procedure (TX: 31, TY: -564).
North Arm Cavity left locked.

the W arm was reopened today at about 13h00LT, the pumpdown is progressing regularly. For now an auxiliary turbo pump is still in use, the system will be fully restored next Tuesday.