ITF found in SINGLE_BOUNCE_SR in COMMISSIONING mode, with SQZ team at work on FIS/FDS injection activity.
Activity concluded at 19:30 UTC. With Spinicelli and Was we recovered the standard state of INJ and DET.
After a realignment of both cavities, I finally acheived LOCKED_ARMS_IR.
During the test injection, the sensor with the best Signal to Noise Ratio is ENV_CEB_ELECTRIC, followed by ENV_CEB_GROUND_CURR_MON and ENV_CEB_GROUND_MAG.
The magnetometers near the towers all detect the Comb signal, in some cases up to three orders of magnitude above the noise floor.
This is expected: the cable running from the TIRA BAA-120W power amplifier output toward the NI suspension rack and, in parallel, toward the SR tower forms a large loop, which generates a significant magnetic field.
This must be considered when evaluating the effect in Hrec: coupling may arise from the magnetic field rather than from currents in the grounding connections, as the field can act directly on the mirror magnets.
When only real ground-current flow is present, this effect should be absent or strongly suppressed, since no large loop is formed.
Last Friday (13th March) we installed the ground current injection setup (pictures 1-6) and we tested it without ITF. Figure 7 shows a scheme. The injection is performed between the electrical ground of the NI SAT crate and the SR vacuum chamber. The driving signal was one 11Hz comb (saw-tooth by the Hameg generator) amplified to approx 0.5 A and 5 V (as read in the display of the TIRA BAA-120W amplifier, and also with one ammeter in series with the resistor). Tips by Robert and Federico: do not exceed 1A, the resistor should not become "hot". Be careful not to swap '+' and '-'. The two ends of the cable out of the amplifier (both black) have been labelled.
The current clamp sensor (ENV_CEB_GROUND_CURR_MON) is described in this entry: https://logbook.virgo-gw.eu/virgo/?r=68265. It was placed around the cable connecting the ground of all platform racks to the CEB hall main ground copper bar. In turn this copper bar is connected to the CEB main copper bar located in the service room next to the main entrance. Finally the latter bar is connected to the safaty earth, which consists of one external ring with ground rods placed all around CEB.
The comb is sensed widespread: by the current clamp (above) and by the ENV_CEB_ELECTRIC probe which is measuring the voltage difference between the WI SAT rack and the WI vacuum chamber.
Figure 8 shows the injection (purple). In the blue curve the current clamp was disconnected from the grounding cable.
During the test injection, the sensor with the best Signal to Noise Ratio is ENV_CEB_ELECTRIC, followed by ENV_CEB_GROUND_CURR_MON and ENV_CEB_GROUND_MAG.
The magnetometers near the towers all detect the Comb signal, in some cases up to three orders of magnitude above the noise floor.
This is expected: the cable running from the TIRA BAA-120W power amplifier output toward the NI suspension rack and, in parallel, toward the SR tower forms a large loop, which generates a significant magnetic field.
This must be considered when evaluating the effect in Hrec: coupling may arise from the magnetic field rather than from currents in the grounding connections, as the field can act directly on the mirror magnets.
When only real ground-current flow is present, this effect should be absent or strongly suppressed, since no large loop is formed.
After open/closing the SDB1 angular could work again. But then in DRMI 3F the correction diverged, and the loop didn't want to close anymore. After some time I have realized that the floating set point have saved a very misaligned position. Reverting to fixed set point the lock acquisition went to LN3 ALIGNED on the first attempt. I have restored floating set point for SDB1 so that they learn again the correctly aligned position for SDB1.
This afternoon, the NCal and associated PCal lines have been moved from near 102Hz to near 18 Hz.
Indeed, the ITF unlocked at 7.40.55UTC because of another glitch of the NI_F0_ACC (see fig. 1).
After that, the MAR controls of SDB1 opened (and so they are yet), see fig. 2.
Maybe, it is better to leave the ITF in Locked_arms.
The interferometer has been systematically unlocking in LOCKING_DARM_IR this morning, with ~10 failed attempts. I have changed the lock acquisition request to LOCKED ARMS BEAT DRMI 3F.
Indeed, the ITF unlocked at 7.40.55UTC because of another glitch of the NI_F0_ACC (see fig. 1).
After that, the MAR controls of SDB1 opened (and so they are yet), see fig. 2.
Maybe, it is better to leave the ITF in Locked_arms.
After open/closing the SDB1 angular could work again. But then in DRMI 3F the correction diverged, and the loop didn't want to close anymore. After some time I have realized that the floating set point have saved a very misaligned position. Reverting to fixed set point the lock acquisition went to LN3 ALIGNED on the first attempt. I have restored floating set point for SDB1 so that they learn again the correctly aligned position for SDB1.
ITF found in LOCKING_ARMS_IR State and COMMISSIONING Mode.
All time are UTC.
15:00 Activity on Attempt to inject SQZ into the interferometer finished (Vardaro, #68877).
15:20 NEB platform activity (Tringali, FIori).
16:16 Recentered MAIN_PLL_dev DMS flag.
ITF struggled to go over CARM_NULL_1F and/or locking the OMC even after the ending of the activity in the experimental buildings.
18:49 ITF reached LOW_NOISE_3_ALIGNED.
ITF left in LOW_NOISE_3_ALIGNED and COMMISSIONING Mode.
This morning I went in DET e room and i realized that the Frequency generator used as actuator of the CC loop was not setted with DC External modulation. I adjusted it Fig1. I also measured the frequency of the Generator in DET E room and the one in INJ Eroom to check if their frequency where similar
After the first lock I setted the CC DAC offset at 0.045 and I managed to close the CC loop and the AA loop. The magnitude of the CC is still 2mV and before the shatdown was higher than 2.7mV
We need to realign everything more carefully. Next week we will continue
ITF found down with the automation blocked: the shutter on B1 was open and DET_MAIN was attempting to close it.
I manually restored the automation, realigned the cavities, and then in CITF I prealigned the SR and PR; the ITF could not pass CARM_NULL_1F.
At around 8:00 UTC we stopped the lock acquisition because not compatible with the other planned activities:
At around 13:00 UTC we relaunched the lock acquisition and again we had troubles in locking the OMC; I contacted the DET on-call and he fixed the issue (see OMC demodulation phases adjusted ).
In parallel Marco worked at FDS recovery.
We noticed that the demodulation phase of the OMC locking error signal B1_PD3 was very mistuned (with the Q signal higher than the I signal). We corrected it by changing the demodulation phase from 0.5 to 1.5 rad. The external configuration file was reloaded at 13h07 utc.
While the ITF was in Low Noise 1, we also adjusted finely the demodulation phase of the B1 error signal, by chaging the phase from -1.3 to -0.7 rad. External configuration file reloaded at 13h17 utc.
As we are considering running with a detuned signal recycling. I went back to this simple parametric model of the DARM response with SR detuned, which has two free parameters, the pole of the response when SR is tuned (in Hz), and the angle of detuning on the circle in the complex parameter space of the pole (which monotonic but not directly related to the SR detuning phase). A question is how to use that model for Hrec, which currently relies on two lines, one at 70Hz and at 360Hz.
Figure 1 shows the changes in the amplitude of the response at 70Hz, for a reasonable range we would explore in both parameters of the model. The changes are very small, at most 1.5%, and depend mostly on the SR detuning angle. The amplitude of that line should remain a good parameter for measuring the absolute scaling of the optical response, that can be affected by the power in the arms, the maching with the OMC, or other type of detection losses.
Figure 2 shows the changes in the amplitude of the response at 360Hz. In that case the amplitude is mostly affected by the pole frequency of the model. In principle it should remain around ~430Hz when detuning, but that gives the freedom for the calibration to follow any changes, for example due to SR misalignment.
Figure 3 shows the changes in the phase of the response at 360Hz. The phase is mostly affected by the SR detuning. So that will be a good measure of the SR detuning for the optical model.
Figure 4 looking at the line at 491.3Hz the phase change of 0.2 rad that was measured during the experiment of Feb 24 corresponds to roughly ~1 of detuning in this parametric model.
This model doesn't include the optical spring at low frequency. In principle the parameters should be related with the SR detuning, in practice I doubt it will be reliable, as the optical spring frequency also depends on the power in the arms, and simulations show it is also affected by the PR and SR RoC mistuning. So there the only solution that seems reasonable to me is to measure the frequency and Q factor of that pole using additional lines at low frequency.
/users/mwas/calib/detunedSRfit/SR_TF_parameter_scan.m
This morning, the NCal and associated PCal lines have been moved from near 36 Hz to near 102 Hz.
A question about the carrier HOM power decrease with SRCL detuning is if it follows expectations. To try to answer that I have simulated the DARM response in optickle for several SRM offsets between 0nm and 20nm compared to the anti-resonant position, and measured the phase change at 491.3Hz with regard to the tuned reponse. In this way the data on the phase of that line can be used to calibrated the SRCL detuning, in units that I can understand. Then that SRM offset can be used in a simple Airy peak calculation of the SRC, to see how the amplification of the HOM changes as the SRC is moved off-resonance for the HOM.
Figure 1 shows the result, during the steps of SRCL offset the B1p power decreases as expected, when assuming a 2% round trip loss for the SRC. For that figure I assume that 65mW of B1p power is due to the 56MHz sideband, and is not affected by the SRCL detuning. This is a number calculated in the past, and also in rough agreement with the ratio of carrier and sideband on the B1p phase camera.
However, that agreement is surprising, as HOM should be seeing a large round trip loss due to 150mm SR diaphragm.
Figure 2 shows what happens if one assumes a 20% round trip loss for the HOM. 20% is a reasonable number, rather on the low side, of the expected losses from the SR diaphragm. With those assumption the B1p power decreases much more quickly than expected.
Note however than when trying to make that analysis, I have several times made mistakes of a factor 2 in the SRCL detuning (whether it is the distance between IM and SR, or if it is the round trip length). I think I have fixed them all, but there could still be an error of the order of a factor 2 somewhere. Also optickle predicts an optical spring at 14Hz for the optical spring, while the optical spring channel measures 9Hz, so the simulations used could just not be a good way of calibrating the SRCL detuning.
/users/mwas/detchar/toySensitivity_20260225/SRCLdetuning_B1p_optickle.m
ITF found stable locked at LN2 in TROUBLESHOOTING mode.
ITF recovery completed. COMMISSIONING mode set at 17:05 UTC.
From 17:00 to 20:00 UTC - Vardaro performed the planned activity on FDS FC recovery. Lock acquisition stable, up to LN3_ALIGNED.
ITF left locked at LN3_ALIGNED in PREPARE_SCIENCE mode.
We starteed to realign the SQZ beam toward ITF.
Preliminary operation
SQZ_MAIN in SQZ_LOCKED_NO_FC, SQZ_FLT in GR_AA
Open SDB1 Shutter before the ITF lock
CC PLL stopped to work: we reduced the starting set point from 29585 to 29500.
Remove SQB1 Retroreflector: at 17:52:38. 300000 steps verticl positive. Then we relaigned mainly in vertical to optimize again the HD 4MHz mag. We measured about 8.7dB of ASQZ and 5.6 dB of SQZ
Removed SQB1 Shutter steps 500k downward at 18:05:21 UTC
HWP Rotated for Injection into ITF at 18:12:40 -32500steps
The interferometer unlocked at: 18:09 UTC
Opening of shutter and check alignment
New lock in LN2 at 18:25 UTC
B1_4MHz 0.18mV
Working on SQB1 M22 and M23 I managed to reach 1.6mV of magnitude but the signal is strange and also the CC error signal is strange. I don't manage to close the CC loop. i also disengaged the active phase noise cancellation loop but I did not improve.
I leave all the shutter open SQB1 and SDB1. Only the fast shutter is closed
This morning I went in DET e room and i realized that the Frequency generator used as actuator of the CC loop was not setted with DC External modulation. I adjusted it Fig1. I also measured the frequency of the Generator in DET E room and the one in INJ Eroom to check if their frequency where similar
After the first lock I setted the CC DAC offset at 0.045 and I managed to close the CC loop and the AA loop. The magnitude of the CC is still 2mV and before the shatdown was higher than 2.7mV
We need to realign everything more carefully. Next week we will continue
The filter cavity is again realigned with IR. The back reflection of the FC toward the HD detector has the same direction of the beam reflected by the retroreflector, this means that the retroreflector is parallel to the FCIM and that the FC can be enabled and disabled but the beam propagation does not change.
Tuesday
We wanted to remove the retroreflector, but the SQB1 PicoMotors process was crashed. Thus tried to chek the SQB1 powersupply process and we noticed that the power supply was not reachable. We went in DET-Eroom and we reloaded the interface of all the power supplies. After that we could reach it from the process but the channel 1 (Pico motors) was setted at 0V. We came back in DET Eroom and we set the channel at 12V, After that we managed to switch on the picomotors process.
We removed the retroreflector by moving -330000 steps RetrorefY.
At that point we went in the state SQZ_LOCKED_NO_FC with SQZ_MAIN, we opened the SC shutter and we unlocked the filter cavity from the green lock. We saw some small flashes with the IR.
We locked the FC on Green and we started to scan the SC PLL frequency from 100MHz and 100.100MHz. This means that the SC frequency is scanned between 1260Mhz and 1260.1 MHz. We saw the TEM00 looking FCEB_IR_Cam. So we reduced the ramp to about 5 kHz around the TEM00. After that acting on SQB1_M21, SQB1_M22, SQB1_M23. M22 and M23 are after the retroreflector so they not impact with the alignment of the IR toward the ITF.
Once we reached about 10V with IR flashes we decided to try to keep the IR in resonance acting on SC PLL frequency and run the IR AA loop.
To do this we used the automation. We have to change three flags, two in SQZ_MAIN: fis_injection from true to false and sqz_flt from false to true and one in SQZ_FLT itf_fis_rr from true to false. Then we asked the state FLT_IR_AA_FMODERR tuned and we managed (skipping FMODERR) to relock everything. We noticed some issue in the DDS (periodical glitchise when we changed the frequency, we asked to Mateusz to solve this issue because it is typical after the restart of the DDS box) We left this state for the night.
Wednesday
We found everything aligned and we decided to check all the demodulation phases. For the green everything was still tuned. For the IR we had to reduce all the pahses by about 0.2 (for QPD) and 0.5 for the longitudinal phase.
We then decided to go towar the HD and we saw that the EQB1_HD_DIFF_4MHz_mag was lower than usual 7mV instead 8.5mV. So we unclipped the beam into the FI using SQB1_M23. Then we re-engaged the FC IR AA in order to do some iteration in both the direction of the FI. At the end we managed to have 8.35mV and about 8.7 dB of ASQZ. We then put again the retroreflector but the IR was completely clipped. We unclipped moving it in horizontal. Once unclipped we managed to obtain more or less the same level of ant-squeezing with and without the retroreflector.
Last step to recover was the FMODERR loop. We asked for a frequency counter to Flavio and we went in DET Eroom to measure all the frequencies of the generator involved in the loop. But for some reason the FMODERR loop was overestimating the length of the FC by 3mm so the FSR by 4Hz and the total frequency of the SC by about 10 kHz.
Thursday
Mateusz solved the issue of the DDS
In DET lab we centered the EQB1 GR Camera, We realigned the PD for IR AA and we centered the PD for GR PDH of the filter cavity.
We measured again all the frequencies of FMODERR (we left the frequency counter to heat up all the night and we also measured again the FMODERR generator calibration.
FMODERR Generator settings: FM modulation 600Hz, Amplitude 0.9Vpp and frequency: 78.919292 MHz
Then we measured everything with Frequency meter:
After that we tried to use also the active legth measurement of the FC to adjust the detuing of the FC and it worked at the first attempt.
Still to be done:
Phase scan with HD and FCIM
Characterize FIS with HD
Some oscillation in the GR IR transmission from FC (to be checked/fixed).
We continued with the ITF's recovery.
We tested the engagement of CARM_SLOW with different a different order of the executed commands, in particular me found that changing the loop's gain in parallel with the ENABLE switch allow for an engagement smooth enough to preserve the lock.
Looking at older versions of ITF_LOCK.py, this is the way the loop was engaged in the automation, before the blackout. Since this procedure is rather unusual, it was probably modified during the recovery.
We restored the older version of ITF_LOCK.py and tested the lock acquisition multiple times, successfully.
We also tried to remove the double phase change for DIFFp in carm_null, but the lock acquisition failed so we reverted the change.
We could reach LN3_Aligned, but the lock was killed by a glitch on the NI accerometer (fig.1), similar to those observed on the BS in the past. This happened at least one more time.
7:00 UTC At the beginning of the shift I found the ITF in CARM_NULL_1F, TROUBLESHOOTING. The weather during the night was stormy, which may have influenced the unlocks between 1:48 UTC and 4:04 UTC.
7:30 UTC Beginning of daily activities: FDS FC recovery (Vardaro), ITF recovery from CARM_NULL_1F (Boldrini, Pinto, Ruggi, Spinicelli)
10:14 UTC Earthquake in Greece, magnitude 4.9, 9km from the surface
14:43 UTC ITF in LN2
At the end of the shift I left the ITF in LN2 with recovery ongoing
This morning, NEN and NWN frequencies have been swaped with the WEN and WWN frequencies. We have now:
The ITF was found in Troubleshooting and in locked arms with the commissioning team working on the ITF recovery, see Status of the ITF.
In parallel, Marco worked on FDS FD recovery; all the activities were stopped at 20:20 UTC.
At 19:54 UTC the ITF achieved a stable lock in CARM_NULL_1F; the ITF will be left in that state for the night.
This morning there were few problems with the lock acquisition regarding a couple of critical points:
1. The hand-off of PRCL from 3f to 1f. It seemed that when the error signal was making the hand-off, the demodulation phase was stil changing causing unlocks. We checked in the logs and indeed that phase change was sent with a ramp of 20s. We hardcoded a ramp of 1 second in the Automation.
2. The engagement of CARM slow loop is very agressive and it causes also some unlocks. We commented these lines and we managed to stay locked in CARM NULL 1f, even with the good phases of the DIFFp (and we fine tuned the phase of PRCL in 1f). We are currently working in the engagement of this loop, which seems to be our stopper.
A look at long averaged coherence between the ground current monitor and hrec_gated, up to 250Hz - Figures 1 and 2:
The two checked times are: 30 Nov 2025 9:00, 6 hrs (current probe at ground rod on the top of electrical panel in front of INJ cryotrap); 22 Feb 2026 2:00, 6 hrs (current probe at ground cable of the BS base).
Similar coherences are found also with magnetometers - Figures 3 and 4:
ITF found in LOCKED_ARMS_IR State and TROUBLESHOOTING Mode.
All times are UTC.
07:04 Unlock at REDUCING_CARM_OFFSET_1_OF_3.
07:14, 07:24, 07:36, 07:46, 08:11 Unlock at LOCKING_CARM_NULL_1F due to saturation of SDB2_B1p_PD2 causing Fast Shutter to close.
08:00 FDS FC recovery activity started (De Laurentis, Vardaro).
ITF left in LOCKED_ARMS_IR State and TROUBLESHOOTING Mode with ITF recovery still ongoing.
