During the afternoon two activities went on: #69785 TCS tuning and #69787 CARM_NULL locking

Activities ended at 20:00 UTC

ITF left in LOCKED_ARMS_IR

In the afternoon shift we noticed a difficulty in locking the DRMI; once we could lock we checked the different steps, and yet again the MICH/SRCL demodulation phase had changed, especially for the 56MHz (and less so for the 169MHz); we checked a few things along the following steps:

• gains were mostly ok, we increased ASC_PR given the sidebands were lower today; both DARM and MICH had also to be increased (the former especially);
• the demodulation phase for DARM was also retuned, although to a lesser extent;
• a first check of the calibration between PD2 and PD1 for B7 was attempted, as we could see that during the swap the level of B7_DC changes; it doesn't look a lot when the change happens (CARM offset 150Hz), but it clearly escalates with the intracavity power; this was done by heart as I couldn't compute the ratio with dataDisplay (it returned a plain zero) nor did I dare to open Matlab during the shift; this will be checked again offline;
• when we managed to get to CARM Null, the PR vertical resonance at 11.6 Hz killed the lock after a while;
• later on, the acquisition up to STEP3 was quite reproducible, but we then faced issues going to CARM Null; a general lack of gains (PR, DARM, DIFFp) that we increased, but the gain of SSFS was quite high and we reduced it (again, to be better checked offline);
• what killed the lock consistently was a quick drift of the carrrier, that we could not explain so far; it happened most of the time in CARM_NULL_3F or while doing the transition to 1F. Sometime we could link it to DIFFp/WE, but not all times so this is not conclusive.

At around 13:30 UTC, we prepared the DET HWS measurement to sense the NI mirror: the INJ HWS beam was turned OFF and the DET HWS beam was set to 1.4V.

After various attempts of lock acquisition up to CARM NULL 1F, we agreed with the ISC team to perform a CH common step. Specifically, at 14:11 UTC both the CH powers have been increased by 20% (STEP 10), as detailed in the table below.

No sufficiently long locks have occurred to allow a measurement with the HWS DET, so the activity will be postponed to the upcoming shifts.

Today, an analysis of the WI point absorber was performed using thermocamera images.

• Fig. 1 shows the reference thermal image selected for the analysis.

• Fig. 2 displays the MATLAB analysis output, highlighting a differential temperature of approximately 0.65 degrees for the point absorber (calculated by subtracting the mirror image in CARM_NULL from the image taken with the ITF in DOWN status).

• Fig. 3 illustrates the reconstructed mirror geometry, featuring the identified mirror center and the point absorber location based on pixel-to-distance mapping.

Geometric Mapping:

• X-Axis (Columns): The mirror center is located at column 388, whereas the point absorber is at column 384. This places the point absorber slightly to the left of the center (a offset of 3.5 pixels in the image, corresponding to approximately 0.5 cm in physical space).

• Y-Axis (Rows): The mirror center is located at row 241, whereas the point absorber is at row 221. This places the point absorber above the center (an offset of 19.5 pixels in the image, corresponding to approximately 3.0 cm in physical space).

• Radial Distance: The total estimated physical distance of the point absorber from the mirror center is approximately 3.1 cm.

Note that because this spatial mapping is reconstructed manually from off-axis thermocamera images, it is subject to geometric projection and pixel-resolution uncertainties. Consequently, this estimate should be considered less precise than the HWS measurement and serves primarily as a qualitative/cross-checking reference.

I will soon perform a similar analysis of the NI PAs.

Today we attempted to recover the lock acquisition after this Sunday's DAS step.

We noticed that sidebands power has decreased at the DRMI step (Fig.1), but despite this the lock acquisition is somewhat workable without the need of any major change, although it tends to fail in STEP_3_OF_3 for reasons unclear.

The lock in CARM_NULL_1F is achievable, but not particularly stable. We noticed that a frequent cause of unlock is COMMp, who attempts to engage far away from its working point, possibly due to a slight misalignment of the SNEB that introduces a large DC offset in the error signal. For the moment, COMMp and the soft loops have been commented in ITF_LOCK.py (lines 4544-4545 for COMMp and 4458-4461 for soft modes)

ITF found in LOCKED_ARMS_IR in COMMISSIONING mode.
Locking in progress up to CARM_NULL_1F after the usual cross-alignment in ACQUIRE_DRMI.

Planned activity:
CARM NULL locking / DAS adjustment (Boldrini)

DET
Both SDB2_B1p_QD1 and SDB2_B1p_QD2 VBias' rearmed and shutter opened several times during the locking attempts.

The following report has been submitted to the On-call interface.

On-call events -> Air Conditioning

Title: Compressore d'aria n. 2 TB in blocco

Author(s): soldani, Pezzimenti

Details:

Allarme ricevuto sabato ore 21, sia da me che dal Reperibile HVAC in turno Marco Tacchi. Telefonicamente e con l'ausilio del DMS e' stato verificato che il compressore n. 2 in TB era in blocco ("mancata ripartenza") ma il n. 1 era correttamente funzionante e l'impianto non ha subito cali di pressione. E' stato deciso che un intervento immediato sul sito non era necessario.
Ho provveduto a ripristinare il funzionamento del compressore n. 2 alle 7:45 circa del mattino successivo (domenica 20/09).

* Note that any files attached to this report are available in the On-call interface.

The following report has been submitted to the On-call interface.

On-call events -> Air Conditioning

Title: Compressore d'aria n. 2 TB in blocco

Author(s): soldani, Pezzimenti

Details:

Allarme ricevuto sabato ore 21, sia da me che dal Reperibile HVAC in turno F. Pezzimenti. Telefonicamente e con l'ausilio del DMS e' stato verificato che il compressore n. 2 in TB era in blocco ("mancata ripartenza") ma il n. 1 era correttamente funzionante e l'impianto non ha subito cali di pressione. E' stato deciso che un intervento immediato sul sito non era necessario.
Ho provveduto a ripristinare il funzionamento del compressore n. 2 alle 7:45 circa del mattino successivo (domenica 20/09).

* Note that any files attached to this report are available in the On-call interface.

The following report has been submitted to the On-call interface.

On-call events -> Air Conditioning

Title: Compressore d'aria n. 2 TB in blocco

Author(s): soldani, Pezzimenti

Details:

Allarme ricevuto sabato ore 21, sia da me che dal Reperibile HVAC in turno F. Pezzimenti. Telefonicamente e con l'ausilio del DMS e' stato verificato che il compressore n. 2 in TB era in blocco ("mancata ripartenza") ma il n. 1 era correttamente funzionante e l'impianto non ha subito cali di pressione. E' stato deciso che un intervento immediato sul sito non era necessario.
Ho provveduto a ripristinare il funzionamento del compressore n. 2 alle 7:45 circa del mattino successivo (domenica 20/09).

* Note that any files attached to this report are available in the On-call interface.

As agreed during Friday's Daily Meeting, we increased the power of all DAS actuators by 20%.

I also switched ON the WI inner ring, which had remained OFF so far, setting it to the minimum power of 120 mW.

The powers corresponding to this new configuration (STEP 10) are summarized in the table below:

The activity was completed at 09:11 UTC. In order to follow the transient, I asked to keep the CITF locked. Then, just as a test, we attempted a lock acquisition up to CARM NULL. The interferometer remained in CARM NULL for a few minutes before unlocking. I left the ITF locked in CITF. Later in the afternoon, I will request Locked Arms on IR.

These results are so far qualitevely similar to the point absorbers measurements done at LMA VIR-0406A-26. 

For WI the LMA measurements had shown one strong point absorber close to the center (-10mm, +24mm) with an expected absorbtion of 7-8mW for 100kW of power in the arms. It was point 5012 of the input mirror scan. 

Analyzing the HWS image from yesterday with the same type of code as the LMA measurements I find that to make a comparable effect to what is on the HWS image, an absorption of 11mW is needed. The power in the arms is currentlny around 80kW, so scaling it to 100kW it correspond to an absorption of 14mW, almost double what was expected. 

Figure 1 shows the HWS image after 10 wavefronts, roughly 5 minutes. 

Figure 2 shows the model of the HWS image after 5 minutes for one point absorber and uniform absorption of 20mW.

Figure 3 shows the difference between the HWS image and the model

Figure 4 and 5 shows vertical and horizontal cuts through the HWS image and the model

/users/mwas/TCS/HWS_image_convolution/image_convolution_WI_IM01_transient.m

For NI several point absorbers with lower absorption are expected from the LMA measurement. Which qualitely is what is seen on the NI thermal camera image, where the points look much less bright than on the WI thermal camera image. A HWS image of NI would be needed to confirm that indeed the NI point absorbers have a lower absorption than the WI point.

In the afternoon, the lock acquisition worked smoothly. Thus, I took some time to check the focus of the NI and WI thermocamera. In addition I also tried to focus the PAY NI Cam.

I could look at the camera images during several lock acquisitions, and those seem to confirm the presence of the WI PA (Fig. 1 and the down in fig 2, tiff and csv data on demand). Unfortunately, also the NI mirror seems to have some points (a clear one on the left part of the image and a fainter one on its right) that shine up with the lock acquisition (fig. 3 and the donw in fig. 4, tiff and csv data on demand).
To be confirmed with further HWS absorption measurements.

In both cases, they start to shine already at step 3/3 (250mW).

I left the ITF locked on the arms for the weekend.

Yesterday evening we raised the WI CH power (STEP 5, around +40%) in an attempt to set the SBs level in CITF back to their maximum values, i.e. around 0.054 mW for the 6 MHz and 0.032 mW for the 56MHz. So the starting point of this morning is summarised in the table below:

Also this morning we made a further action, this time on the NI CH; we performed two steps:

• STEP 6, NI CH power +18%, at 7.23 UTC

• STEP 7, NI CH power +18%, at 7.42 UTC

Since STEP 7 decreased the 12 MHz signal, we partially reverted the change by 9% with respect to STEP 7.

After these two steps, we resumed the lock acquisition attempts up to CARM NULL. After several attempts, which consistently unlocked at the same stage of the lock acquisition, the ISC team solved the issue by adjusting some lock acquisition parameters.

At 08:31 UTC, CARM_NULL_1F was reached and the lock lasted for about 30 minutes.

Figure 1 shows a comparison between this CARM_NULL_1F lock (08:31 UTC, lasting about 30 min, blue and orange lines) and the one obtained yesterday (17/09 at 14:14 UTC, lasting about 25 min, purple lines). The DAS STEP3 improved the sideband level, as can be seen from the comparison.

After the 08:31 UTC lock, we were not able to lock again due to a vertical oscillation of the PR mirror at around 11 Hz, similar to the one observed yesterday (69770). We therefore called Paolo for support.

At 10:38 UTC, following Paolo's indications, Diego managed to reach CARM_NULL_1F again.

From this point on, the CARM_NULL_1F lock became reasonably reproducible. Thanks to Diego, we also recovered the automation for the gentle unlock. After a few trials, we were able to perform the planned HWS-INJ measurements, manually unlocking the interferometer when needed.

A PA signature is visible in the HWS-INJ maps in two different measurements: during the lock acquisition (heating phase) and after the unlock from CARM NULL (cooling phase), as shown in Fig. 2. In the same figure, the CH measurement reported in entry 69694 is shown as a reference for the mirror center. From this preliminary comparison, the PA appears to be reasonably close to the center of the mirror. A more detailed analysis of the acquired data will follow.

We left the following TCS settings:

Today around 15:12 UTC we changed the etalon setpoints:

• NI: 20.207 degC in 172800 s (48 h)
• WI: 19.60 degC in 172800 s (48 h)

ITF found in LOCKED_ARMS_IR and in COMMISSIONING mode.

Planned activity:
CARM NULL locking / DAS adjustment (Mantovani, Bersanetti, Spinicelli, TCS crew).

- ITF relocked up to CARM_NULL_1F after the usual cross-alignment in ACQUIRE_DRMI.
At the end of the morning TCS tuning, I set "False" at line 17 in the ITF_LOCK.ini and restarted the lock acquisition. ITF acheived easily CARM_NULL_1F.
DAS adjustment in progress...

DET
06:05 UTC - Both SDB2_B1p_QD1 and SDB2_B1p_QD2 VBias' rearmed several times during the locking attempts.

ITF found in COMMISSIONING Mode and LOCKING_CARM_NULL_1F State with activity on CARM NULL locking / DAS adjustment ongoing.
The activity went on up to 19:38 UTC (#69770).
ITF left in COMMISSIONING Mode and LOCKED_ARMS_IR State.

 

This morning, we continued the tuning activity started yesterday (69761). 
The initial TCS settings are summarized in the table below.

The CARM NULL locks were limited by a vertical oscillation of the PR at around 11 Hz, which was causing the ITF to unlock. Paolo and Manuel took care of the issue and managed to solve it.

At some point, we also experienced a few unlocks due to the green losing lock. This issue was investigated and solved by Piernicola.

At this point, since the B1p fringe was already quite dark (~0.016 mW), we decided to try a common step on both DASes in an attempt to increase the sideband power. We therefore decided to increase both the WI and NI DAS powers by 20% at 14:42 UTC (STEP 3)

Unfortunately, shortly afterwards, the ITF unlocked due to an earthquake, which prevented further lock acquisition attempts for some time (earthquake at 14:19 UTC).

Once the earthquake transient had approximately settled, we noticed that the sideband powers in CITF had decreased by about 10%.

ISC then attempted two lock acquisitions, but both failed at the same step (CARM offset, step 3/3).

Therefore, before retuning the lock acquisition, we decided to also increase both the WI and NI CH powers by 20% (STEP 4, at 16:25 UTC).

The sideband increased but not recovering the level before the STEP 3. Some attempts were made to reach CARM NULL, but we did not manage to reach it. The ITF always unlocked at the same step (CARM offset, between step 2 and 3).

The final CO₂ laser configuration is summarized in the table below.

We could not recover CARM_NULL_1F after the TCS steps: the lock parameters need a more careful tuning after these changes.

Presently, the lock breaks at step 2/3 of the CARM offset reduction.

We also undid the change in the /virgoDev/Automation/PyALP/PyUGF/algo.py, resetting the UGF servos step to ±\pm5%

Figure 1 and 2 shows two screenshots from the video of WI. One towards the end of the CARM NULL lock and well before. Jumping back and forth between the two pictures there is a faint absorber visible in the middle of the image. And that point disappears shortly after the unlock. 

Figure 3 shows that faint point circled.

Figure 4 and 5 shows the same type of analysis for the NI video. There I cannot notice any points, but it might be harder to notice on the color videos than on the black and white one.

In the following, the link to NI and WI thermal cameras videos of yesterday's lock acquisition starting around 14:39 UTC, CARM NULL (of around 40 seconds) and a brief time after, together with main ITF signals.

https://owncloud.ego-gw.it/s/NDrWctmKC5ebyb4 

As already observed (69742), there is no clear evidence of PAs.

ITF found locked in CARM_NULL_1F in COMMISSIONING mode.
The planned activity on: CARM NULL locking / DAS adjustment (Bersanetti, Mantovani) started at 07:00 UTC. Still in progress...

Another comparison of ITF signals during two different CARM NULL acquisitions:

• 11 September, around 15:17 UTC, less than 10 minutes long: without TCS [purple curves]

• 17 September, around 06:58 UTC, around 20 minutes long: with TCS, while tuning was ongoing [blue and orange curves]

In the plots containing two superimposed signals for each acquisition, the two reference curves are both shown in purple. They can be matched to the corresponding blue and orange curves by their relative vertical position: the upper purple curve corresponds to the upper curve in the TCS-on data, and likewise for the lower curves.

Overall, all the monitored signals appear to have improved after the initial TCS tuning, with the exception of the B1p 6 MHz balance.

The commissioning activity on CARM NULL locking /DAS tuning proceeded through the afternoon until 19:30 UTC #69761

The ITF was able to stay in CARM_NULL_1F for 20 minutes from 19:41 UTC to 20:01 UTC and another 21 minutes from 20:29 UTC to 20:50 UTC

21:00 UTC At the end of the shift it was left in LOCKED_ARMS_IR

Guard Tour

20:02 UTC

During the day, we will try to stabilize CARM NULL 1F with the goal to have the possiblity to tune the DAS directly at CARM NULL.

The starting point is the following:

We performed some tuning attempts. The first step regarded the CH. 

We increased CH powers by 18 % at 9.24 UTC.

At this point, we were able to reach CARM NULL 1F quite systematically. However, the ITF was repeatedly unlocking because of the high power on B1p, which exceeded the threshold for triggering the fast shutter (0.2 mW).

We therefore contacted DET to slightly increase the B1p DC threshold. Michal increased it from 0.2 mW to 0.25 mW.In parallel, in an attempt to reduce the B1p fringe, at 12:26 UTC we increased the WI DAS outer ring power by a factor of 2, assuming that the WI absorption is approximately twice that of the NI.

After that, we realized that the DIFFp loop had not been working properly since yesterday.

The issue was fixed, and we continued with the lock acquisition tuning. However, we then noticed another problem with the COMMp loop and decided to keep both the COMMp and SOFT loops open.

With this configuration, we were able to reach CARM NULL 1F and maintain the lock for about 10 minutes.
In the first figure, the two CARM NULL locks with and without TCS are shown. The situation seems to be improved at the sideband level.

Concerning the etalon, the sinusoidal behavior is clearly visible. The increase of 112 MHz observed in the upper-right corner of the plot shown in Fig. 2 is due to the change in the DAS settings.

 

ITF found in locked arms IR.

At around 7:30 UTC started the planned activity on CARM NULL locking /DAS tuning; the activity went on without major issues and it is still in progress at the end of the shift.

DMS / TCS

The TCS flags have been tuned and readjusted to take into account new configurations provided by the experts.

LSC

2026-09-16 07h51m06 UTC    berni 'NI:NI Set point [NI_RH_SET=19.85,rampTime=3600]' sent to LSC_Etalon_Acl