After the recovery of the ITF following the installation of the SR baffle, the interferometer unlocked several times, some of them were clearly indicating the PSL/INJ as source of unlock. 

One of the main concern about is the temperature change of the main laser, as in the past the ML temperature setting has been associated to glitches and instability of the laser.

During the night between 12th and 13th there were two unlocks similar to fig. 1. Here, there is an clear instability in the EOM corrections as well as in all the frequency and power error signals. Not clear who is the culprit. 

Instead, the 14th just before the problem of the slave laser, the behavior was different (fig. 2), and it seems that the PMC/PSTAB loop react before everything else. 

On the 12th evening, another unlock seemed to be related to the INJ system (fig. 3 and 4), however no PSL/INJ seem to see anything, except for the MC mirror Z that starts to drift away. No clear reason has been found yet. 

On Saturday evening, the slave laser switched off while. The system was in standby for the weekend ; this morning we went to EER to investigate the issue.

The safety chain had been triggered due to a faulty temperature controller, namely the controller of diode 1.

We installed a spare controller. As usual, the programming procedure is not straightforward; additional information for possible future interventions is provided at the end of this entry.

We were eventually able to restart the slave laser. We gradually increased the current of the pumping diodes and returned to a relatively normal operating condition. The output power of the Neovan is slightly lower than usual, and the mismatch in the PMC is slightly worse (Normalized reflected power 5% higher). We will perform fine tuning tomorrow.

In addition to the information already provided in entries 66004 and 62780, we add the following details:

• The communication addresses are:

  • diode 1: 27

  • diode 2: 1

  • xtal 1: 2

  • xtal 2: 3

• To access the third menu (PID parameter settings), one must press the right buttons simultaneously, then when “Ulock” appears one should use either 0, 1, or 10 (the value depends on user access rights).

• At present, the controllers appear to be configured with the following Ulock values (tbc)

  • diode 1: 1

  • diode 2: 0

  • xtal 1: 10

  • xtal 2: 10

As observed previously, the safety chain reset did not initially work because the start button on EER1/C3 also needed to be pressed. It is unclear whether this action was possible from the beginning or only after off/on of the 6 V power supply (the unit with the red switch).

ITF found DOWN in TROUBLESHOOTING mode.
The ISYS system found DOWN with Slave Laser off and DET_MAIN Metatron node stuck in UNKNOWN state. Experts informed.
Gosselin, DeRossi, Ballardin replaced the TempController in EERoom at 11:30 UTC. Laser again ON.
Upon concluded the recovery of the injection system I set DET_MAIN Metatron node in SHUTTER_CLOSED, ITF_LOCK in EXEC and I started to recover the alignment of both cavities. In particular the NE.

COMMISSIONING mode set.

Relocked at CARM_NULL_1F at 14:56 UTC, after the usual cross-alignment in ACQUIRE_DRMI and after several unsuccesfully locking attempts.

SBE
13:00 UTC - SWEB vertical position restored via stepping motor.

DAQ
14:01 UTC - BaDAQ process crashed / restarted via VPM

DET
14:21 UTC - SDB2_B1p_QD1_GALVO closed via VPM
14:30 UTC - I rearmed Vbias and open shutters for B1pQD1 and B1pQD2.
14:45 UTC - SDB2_B1p_QD1_GALVO, B5_QD1 closed via VPM

We installed one accelerometer and one microphone inside the 1500W building. 

One meggit accelerometer is placed on the concrete floor, veritcally oriented, close to the INGV gravimeter inside the Fiber Lab: picture 1.

• channel name is SQZ_ACC_1500W_SQZ ADC, more info in https://apps-online.virgo-gw.eu/squeezing/?r=857

One GRASS AZ46 microphone  is placed in the Bd. hall: picture 2.

• channel name is W1500_ENV_1500W_MIC, it is read from the DAQ box used for the ROBOT* sensors: https://vpmrd.virgo.infn.it:40000/main.html, W1500_dbox, W1500_ADC0

Figure 1. The test of last week of adding an SRC length detuning was able to improve the BNS range by 6 Mpc from ~38Mpc to ~44Mpc (15% increase). At the same time the B1p power decreased from 265mW to 225mW (15% decrease), and the power in the arms increased by 1% (probably due to less losses to the order 8 and 9 mode).

The DCP as measured by Hrec decreased from 430Hz to 380Hz, and the phase of the 491Hz line in DARM as measured by ASC_DCP_HF_B1_phi changed by ~0.05 radian. The two are roughly consistent with each other and would correspond to a 7nm SRC length detuning using an analytical calculation from André Thüring PhD Thesis.

What is a bit surprising is that the amplitude of the 491Hz line increases by around 1%.

Figure 2. Looking at the analytical DARM response for 7nm and 0nm SRC detuning, the ratio is supposed to increase only in the 100Hz to 400Hz band by 1%. So the DARM response change doesn't seem to be a good explanation as at 491Hz, it is supposed to decrease by 1%.

Maybe the right explanation is that SDB1 turns by 3 urad following the SRC detuning.

During the night after the NE RH was restarted the interferometer was locked in LN2.  https://logbook.virgo-gw.eu/virgo/?r=68655

Figure 1. Shows that during that night the B1p power decreased from 300mW to 180mW, as expected as the time scale for the full RH transient is of the order of 12 hours. The optical gain has also increased slightly by ~1% and the power in the arms, which might be also explained by the mode matching between the two arms improving as the ring heater thermal deformation arrives to its normal working point. However there was no significant change in the BNS range with an increase of less than 1Mpc. This shows that the EM differential RoC matching doesn't play a role in the mystery noise, as has already been observed a few years ago.

Despite that, the 15cm SR diaphragm has clearly shown that HOM are the vector of the 1/f^{2/3} noise, and the conclusion is that the dominant HOM that we see on B1p are not the ones that cause the mystery noise. The reason is most likely that HOM we see on B1p are mostly in the contrast defect quadratures, due to the difference in amplitude between the two beams interfering at the beam splitter. While DC read-out is in the quadrature corresponding to the difference in shape between the two beams at the beam splitter. That DC read-out quadrature can also have HOM, and they don't seem to be related to the contrast defect HOM, by which I mean they are not just a coupling of the contrast defect quadrature HOM due to phase fluctuations, but have an actually different physical origin.

Figure 2. Shows the results for the scans of the EDB OMC that were happening that night, as expected the dominant power was in the order 2 mode, and has decreased by a factor 3 during the night.

Figure 1. The temperature of the NI etalon control started dropping today. Looking at the monitoring of the heating belt output it became intermitent.

This issue has appeared several times in the past and was solved by replacing the Kert power supply: https://logbook.virgo-gw.eu/virgo/?r=67582

We should consider starting to make the replacement of these power supplies on fixed schedule based on past expererience (for example changing them every year or two) instead of waiting for the power supply to fail and then have a thermal transient in the etalon loop lasting a for several days.

ITF found in COMMISSIONING Mode and LOW_NOISE_3_ALIGNED State.
All times are UTC.
14:30 - 16:00 Test of reduction in SDB1 angular set point drift control loop gain (Was, #68684);
18:20:37 Unlock;
18:44:58 Unlock at the end of CARM_NULL_1F;
18:58:10 Unlock at LOCKING_CARM_NULL_1F;
19:31:41 Unlock from ACQUIRE_LOW_NOISE_3_ALIGNED;
20:09:50 ITF reached LOW_NOISE_3_ALIGNED;
20:23:03 Unlock, DET_MAIN Node went in UNKNOWN State, I restored it Requesting INIT state and then SHUTTER_CLOSED;
21:01:38 ITF reached LOW_NOISE_3_ALIGNED;
ITF left in LOW_NOISE_3_ALIGNED State and COMMISSIONING Mode with AUTORELOCK_FAILSAFE engaged.

Today between 14:30 UTC and 16:00 UTC I have reduced the gain of the SDB1 angular set point drift control loop by a factor 4.The motivation is that the angular motion of SDB1, especially in TY, looks correlated with the BNS range and with the optical gain fluctuation measured by Hrec.

Figure 1 shows the result compared with beferoe and after. The fluctuations on SDB1 LC TX/TY decrease when the drift control has lower gain, but there is no change in the BNS fluctuation, DARM gain fluctuations, or anything else.

An interesting comparison can be done with old data taken with an intermediate SR TY misalignment. Fig 1 shows the comparison when the DCP is about 270 Hz: the mystery noise is clearly lower. Fig 2 shows that the working point is quite similar, according to the DCP and the optical gain; now the dark fringe is much darker.

As we know, in the past the mystery noise was lower with a higher misalignement (fig3); now, going further with the misalignament the curve does not change in the region where the mystery noise is supposed to be limiting (fig 4). To be noticed that there is still an improvement of the dark fringe when the DCP is pushed down (fig 5).

A rough estimation of the noise components (fig 6) says that a pessimistic estimation of the thermal noise (0.7e-23  @ 100 Hz) is almost sufficient to explain the curve.

ITF found unlocked with both cavities misaligned; to realign them I had to move the PR. The ITF relocked at the first attempt in LN3_Aligned.

At 9:30 UTC Paolo made some test to acquire data with SR misaligned in different steps.

At 13:28 UTC, following Maddalena's instrunctions, I changed the Etalon setpoint:

•  NI:NI Set point [NI_RH_SET=18.66,rampTime=3600]' sent to LSC_Etalon_Acl
• WI:WI Set point [WI_RH_SET=18.82,rampTime=3600]' sent to LSC_Etalon_Acl

ITF left locked in LN3_Aligned.

Same plots again, where yellow dots now include this morning's scan of the SRM angle. It seems that the strain noise at 110÷133 Hz is flat below 300 Hz DCP frequency. And the effect above 300 Hz DCP is mostly due to optical gain, i.e. the net broadband noise in power units does not change significantly when misaligning SR. 

Starting form 9:30 UTC, for two hours some data have been acquired with SR TY misaligned in many steps, up to the usual 2 urad which sets the DCP below 200 Hz. The aligned state with SR TY in loop has been recovered at 11:35 UTC.

To continue on this cleanup exercise also the GUI applications Chassis and CenteringUI have been removed from the SUS IceWM menu since not working or not in use anymore.

At the beginning of the shift I found the ITF in LOCKED_ARMS_IR, TROUBLESHOOTING, with inj team working on the RFC aligment
15:30 UTC beginning of relocking activity: west green laser's thresholds adjusted (Bersanetti), high sea activity  SR guard opened, NI F0 H3 had to be adjusted (Palaia). ITF kept unlocking between LOCKED_ARMS_IR and CARM_NULL_1F. After a thorough investigation by Bersanetti, Pinto and Was it was necessary to move SR by +10 urads tx and +5 urads ty and the ITF locked
21:00 UTC ITF in COMMISSIONING, LN3_ALIGNED
21:37 UTC unlock
22:00 UTC end of shift, ITF left relocking with AUTORELOCK_FAILSAFE

On-call intervention as the H3 coil on NI F0 was approaching saturation (Sa_NI_F0_COIL_H3 value around −9 V).
After the intervention, the correction values were restored to about 0 V.

• Start time: 18:25 LT
• End time: 18:40 LT

We made a characterization of the noise changes related to the replacement of the UPS at the NEB occurred on Dec. 9 2025, https://logbook.virgo-gw.eu/virgo/?r=68330.

The noted changes are very similar to what noted for the similar replacement of the UPS of WEB occurred on July 1st 2025, and described in the elog "Noise measurement of the new UPS units installed in the NEB".

We noticed:

• the largest noise change is seen in the UPS monitors, magnetometers see tiny ones
• Figure 1, Figure 2: a peak at 1.4 Hz and +-1.4 sidebands in odd 50Hz harmonics disappear form voltage and current monitors, some reduction at 1.4 Hz is seen as well by magnetometers
• Figure 1: the low frequency (below 200Hz) part of UPS Voltage and currents monitors clean significantly, up to the point that current monitors are now dominated by sensor noise at all frequencies
• Figure 3: the high frequency part does't clean much, and actually some noise increase in visible.
• Figure 4, 5, 6: two narrow peaks at 50Hz +-6Hz (Figure 4) and slowly oscillating in amplitude (Figure 5), appear in the Voltage monitors: these peaks were present also before but just in the IPS monitors (Figure 6)

Note: UPS Currents Probes need to be replaced with more sensitive ones.

Yesterday evening, for no apparent reason, the SL switched off.

This morning we went to EER to investigate. The safety chain had been triggered; after resetting it, the SL switched on without any issue. It then took some time for the system (SL, AMP, PMC) to thermalize, and some power was initially missing at the PMC and IMC outputs.

While attempting to speed up the recovery by increasing the power with IPC1, we noticed that we could not reach the nominal 18 W in IMC transmission. We suspected we were limited by the IPC1 transmission power, especially considering the PMC transmission decrease observed in December (#68408). We therefore went to the laser lab to recover the power discarded by IPC0.

We managed to increase the PMC transmission by about 10%, although this came with a 20% increase in reflection. As a result, the IMC transmission rose slightly above 19 W.

We then attempted lock acquisition again and realized that the limitation was not due to IPC1 transmission power. Instead, the IPC1 rotator server was not responding. We went to Piscina, rebooted the rotusb1 server, restarted the EIBAgilisRot server, and IPC1 resumed normal operation.

During lunch, we continued with lock acquisition, but INJ was quite unstable, most likely due to the PMC loop not being retuned after the power increase.

Since IPC1 power was not the issue, we decided to (approximately) revert the power previously recovered from IPC0. While there, we realigned the beam inside the PMC. After realignment, we measured the higher-order modes:

• TEM20 ≈ 20/800 mV/mV (~2.5%)

• TEM30 ≈ 30/800 mV/mV (~3.7%), which is unexpectedly high.

At this point, triggered by this TEM30 and noticing that PMC transmission, IMC error signal and PSTAB were quite noisy (approximately a factor 3 increase on PMC TRA, figure 1), we decided to try to improve the situation by adjusting the Neovan pumping diode currents.

We changed the Neovan pumping diode currents from (5.2 A – 5.0 A) to (5.0 A – 4.9 A). This produced a significant improvement in overall system performance (figure 2)

• AMP output power decreased from 0.375 V to 0.36 V

• PMC transmission increased from 0.775 V to 0.782 V

• PMC reflection decreased from 0.17 V to 0.14 V

• Normalized PMC transmission increased by ~3%

• Normalized PMC reflection decreased by ~15%

• Additionally, the Neovan head temperature decreased by 0.6 °C

Overall, this adjustment seems to have a clearly positive impact on system stability and noise.
We keep those values and went on with the planned activity which was the RFC realignment (dedicated entry)

After replacing the communication bridge to the PZT driver (#68586), we attempted to realign the RFC using the two PZTs directly from the VPM.

Both drivers are now in online mode and can be controlled directly via the VPM. This is done through the PiezoApp server in the INJ section of the VPM.

The channels used to move the PZTs are:

M15_axis_x
M15_axis_y
M16_axis_x
M16_axis_y

The status can be monitored through channels such as INJ_M15_axis_x_pos, INJ_M15_axis_x_Reqpos, etc.

We explored both axes of both PZTs to maximize the coupling. Giving the drift of the past months, we hoped not to be limited by the 120 V range limit of M15_y, as has historically been the case; however, this limitation still applies.

Nevertheless, we managed to improve the RFC TRA from 2.7 V to 3.4 V.

ITF found in Commissioning mode and locked in LOW_NOISE_ALIGNED.

Under request of the commissioning team at 14:54 UTC I launched the script inject_asc_test.pyat 15:17 UTC the script inject_lsc.py.

After that the ITF was manually realigned and relocked in LN2 for ITF characterization.

Under request of Julia at 19:30 UTC I manually unlocked to relock the ITF in LN3_Aligned.

Unfurtunately at 19:50 UTC, during the lock acquisition the Slave Laser switched off.  I contacted the INJ on-call ; I went to the EE room and, through a video call, we verified that there were no evident damages or potentially dangerous situations. It was decided to leave the system in this state; the INJ experts will investigate tomorrow morning.

ITF left in DOWN and in Troubleshooting mode.

Since the recovery was already finished by the morning, we started with some characterization of the interferometer. The operator (Berni) launched one set of angular noise injections and one set of longitudinal noise injections at the beginning of the shift. Then Piernicola went to turn on and off the power supply for EDB. After his action we unlocked and relocked in LN2.

Then we started with the SRCL SET scan. We put the BS in full bandwidth and we opened the SRCL_SET loop. Then we starte a scan towards lower SRCL offsets. We waited 20minutes between each point.

• Reference time: 1454862497 – SRCL_SET_TOT  = 40.7 – DCP = 424
• 1st point (-5, START 16:34:32 UTC): 1454864091 - SRCL_SET_TOT = 35.8 – DCP = 432
• 2nd point (-10, START 16:57:10 UTC): 1454865528 – SRCL_SET_TOT = 31.2 – DCP = 422
• 3rd point (-15, START 17:23:03 UTC): 1454867052 – SRCL_SET_TOT = 25.5 – DCP = 423
• 4th point (-20, START 17:47:32 UTC): 1454868509 – SRCL_SET_TOT = 20.5 – DCP = 414.5
• 5th point (-25, START 18:13:07 UTC): 1454870228 – SRCL_SET_TOT = 15.5 – DCP = 410

Then I put the offset to 0 with a ramptime of 20 minutes.

After Piernicola restarted the EDB pico-motor driver I have realigned the EDB OMC between 17:30 UTC and 18:00 UTC. The power of the 56MHz USB increased from 0.2mW to 0.6mW on EDB B1t. It back to the same value it was two weeks ago, and during a scan I couldn't see clearly the amplitude of the order 1 mode of the 56MHz USB, which means it has at least a factor 10 less power than the TEM00. I have turned off the pico-motor process on VPM.

I have left the EDB OMC scanning with the standard parameters freq 0.0005Hz, ampl 0.5, offset 23.27