Figure 1 shows the scan of the OMC performed from 17h05 utc to 17h30 utc, after waiting for 1 hour in CARM_NULL_1F.

Figure 2 shows a zoom of this scan around a Free Spectral Range.

In this FSR, assuming a calibration factor of about 4800 for B1_PD3, we have: ~48 mW on the first order mode, ~24 mW on the second order mode, ~125 mW on the third order modes, ~170 mW on the fourth order mode, around ~40 mW on each of the 5th and 6th order modes, ... Overall, all high order modes are reduced compared to the measurement performed one week ago ( https://logbook.virgo-gw.eu/virgo/?r=64206 ).

Focusing on the 2nd order mode which appears 4 times during the scan, its power is ranging between 24 and 40 mW which is quite similar to the range of values found last week.

Attached figures show the lock of the OMC and the OMC scan performed by Fabio during the maintenane this morning.

The power on B1_PD3 (about 13 uW) when OMC is locked is close to the nominal one. The scan shows that the OMC is misaligned by ~19% (the alignment offsets used for single bounce are not well tuned). This is the same kind of misalignment than what we had two weeks ago ( https://logbook.virgo-gw.eu/virgo/?r=64165 ).

We can also note that the B1_PD1 and B1_PD2 photodiodes have their shutter closed as it should be.

The goal of the shift was to characterize the ITF working point with the following RH powers:

The actions performed during the shift are listed below:

13.08 UTC: ITF relocked in LN3

14.18 UTC: ITF manually unlocked to perform input beam mode matching measurement with the free swinging technique and green laser scan (performed by Suzanne, Camilla and Matthieu).

                    See detailes in 64204

15.03 UTC: ITF relocked in CARM NULL 1F

16.08 UTC: OMC scan started (performed by Romain and Andrea)

16.30 UTC: OMC scan ended 

16.52 UTC: ITF relocked in LN2

After 1.5 hr in LN2, at 18.20 UTC, Andrea will proceed with the lock acquisition.

The main ITF signals during this afternoon are shown in figure 1.

Figure 1 shows the scan of the OMC performed from 16h08 utc to 16h30 utc, after waiting for 1 hour in CARM_NULL_1F.

Figure 2 shows a zoom of this scan around a Free Spectral Range.

Assuming a calibration factor of about 4800 for B1_PD3, we have: ~75 mW on the first order mode, ~29 mW on the second order mode, ~200 mW on each of the third and fourth order modes, ~70 mW on each of the 5th and 6th order modes, ...

In order to try to mitigate this problem, we have increased the shutter pulse duration from 20 ms to 40 ms for both B1_PD1 and B1_PD2. The SDB2_dbox_bench process has been reloaded at 14h52m27-UTC.

This morning, the threshold on SDB1_slow_shutter_OMC1_T1_fast_RMS used to monitor the closing of the slow shutter has been adjusted to 6e-9. DetMoni restarted at 07h19m23 utc.

Here is the quick analysis of the OMC lock and scan performed by the operator during the last maintenance:

https://logbook.virgo-gw.eu/virgo/?r=64135

Fig.1 shows the OMC lock. We reach about 13.7 uW of power on B1_PD3 when the OMC is locked on the carrier TEM00.

Fig.2 and Fig.3 show the OMC scan in temperature. The first order mode peak is about 14% of the TEM00 peak, which is not a very good alignment (this means that the offsets used for NI single bounce are not well tuned), but sufficient for this type of sanity check.

This morning, from 7h00 utc to 8h10 utc, we have added the channels slow_shutter_OMC1_T1_slow and slow_shutter_OMC1_T1_fast in the SDB1_OMC process. They will be used from now to monitor the state of the OMC slow shutter.

The channel slow_shutter_OMC1_T1_fast monitors the closing of the fast shutter (see Fig.1) which is presently done with the "MOVETOLIMIT" command at a speed of 1700 steps/s. The RMS of this channel is now used as observable in DetMoni to check if the shutter motor has stopped after the closing which is supposed to take place only when the ITF is DOWN in standard operations. Thus, if the ITF_LOCK index is above 1 and if the RMS of slow_shutter_OMC1_T1_fast indicates that the shutter is still running, a red flag will be triggered in the DMS.

The channel slow_shutter_OMC1_T1_slow monitors the opening of the fast shutter (see Fig.2) which is presently done with the "MOVEREL" command at a speed of  666 steps/s. The RMS of this channel is now used as observable in DetMoni to check if the shutter motor has stopped after the opening which is supposed to take place only at index 109 of ITF_LOCK. Thus, if the ITF_LOCK index is above 109 and if the RMS of slow_shutter_OMC1_T1_slow indicates that the shutter is still running, a red flag will be triggered in the DMS.

Since we had to start/stop the SDB1_OMC process several times for these operations, we verified at the end of the activity that the demodulation phase of the OMC locking signal was still correctly tuned (Fig.3).

We have updated the Shutter flag in the DMS (configuration of process DetMoni). In case the slow shutter motor remains stuck after step 109 of the lock acquisition, a red flag will be displayed.

We plan to further update the flag logic at the next maintenance to also perform some checks during the lock acquisition after the shutter closure.

This afternoon we performed a few tests on the OMC shutter with the ITF in NI single bounce in order to find a solution to the problem of OMC shutter getting stuck at the opening.

Fig.1 shows a test when sent a MOVETOLIMIT command via VPM to open the shutter. In this case the shutter motor get stuck, and we stopped it by sending the STOP MOTION command.

We have tested the opening of the shutter by sending some MOVEREL commands with a defined number of steps. We have found that with about 36000 steps the power on B1s reaches a plateau. Adding a bit of margin, we decided to perform 42000 steps to open the shutter. This is tested on Fig.2. We can see that it takes about 65 seconds to accomplish this motion.

We have then replaced the MOVETOLIMIT command by the MOVEREL command for the opening of the shutter in the class SHUTTER_OPENING of DET_MAIN. In the DET_MAIN.ini file, we have added the parameter nominal_open_steps = 42000, and we have updated the opening_duration to 80 seconds.

The opening and then closing of the shutter are tested with the automation on Fig.3. The closing is still performed with the MOVETOLIMIT command in order to be sure that we always start opening the shutter from the same position.

It was then possible to relock the ITF in Low Noise 3 at first trial.

The attached Figure 1 shows the time when the OMC shutter was opened for the OMC lock and scan during the last maintenance. One can see a glitch on SDB1_OMC1_T1 indicating when the shutter starts to move. The power reaches a plateau on B1s about 16 seconds later. But, as already mentioned by Michal in https://logbook.virgo-gw.eu/virgo/?r=64012 , the line at 1721 Hz on the spectrum of SDB1_OMC1_T1 is present for about 20 minutes indicating that the shutter motor was still working during all this time. The line disappear between 06h39 and 06h40 utc (see Figure 2).

Figure 3 shows the closing of the OMC shutter. In this case we can see a first glitch on SDB1_OMC1_T1 when the shutter starts to move, and a second glitch about 35 seconds later when the shutter stops. The power on B1s reaches zero about 22 seconds after the first glitch. In this case the line at 1721 Hz on SDB1_OMC1_T1 disappear right after the second glitch, meaning that the shutter motor is properly stopped (Fig.4). Thus, it looks like the end limit sensor is still working for the shutter closing. The issue seems to be only for the opening.

The first lock at 16h00-UTC was luky as  the OMC lock noise disappeared just after the OMC lock with B1_PD3_Audio (plot) but not the others ones  (ie 21h50m-UTC one)

Here we report a few more observations concerning the excess noise causing problems to reach DC readout.

The excess noise is visible on the audio channels of several photodiodes (Fig.1 and Fig.2): B1s, B1sP and B1_PD3 (which are on the same service mezzanine) as well as on the B1p_PD1 audio channel (however in this later case, only lines are present, while for B1s and B1_PD3 there is a clear impact on the noise floor).

As reported already by Diego, an extra noise is also present on the SDB1_LC_TX_err and SDB1_LC_TY_err signals at the same time as the noise is present on the photodiodes. This SDB1_LC_TX/TY_err signals are constructed from the SDB1 B5 QD2 H and V signals, which also see the extra noise. This observation concerning the SDB1 local control was already true yesterday (Fig.3)

Both the spectrum of the B1_PD1 audio channel, and those of SDB1_B5_QD2_H/V signals are clean when we are in CARM_NULL_1F (Fig.4).

The extra lines on B1p_PD1 and the extra noise on the B5 QD2 signals show up as soon as the OMC shutter is open (Fig.5). The lines showing up on B1_PD1 are at the same frequency as the lines seen on B1s (Fig.6), although the B1s noise floor changes when the lock of the OMC is acquired.

The following plots shows a 300s FFTTime of the SDB2_B1p_PD1_Audio, SDB2_B1_PD3_Audio and the  SDB2_B1s_PD1_Audio channels during the OMC lock acquisition where the purple rectangle highlights  the periods with the presence of unexpected lines

• successfull OMC lock
  • 2024-04-01-00h45m00-UTC : FFTTime plot
  • 2024-04-04-13h34m00-UTC:  FFTTime plot,
    • this FFT plot compare the ASD  of the related channels (Audio and sample) for 2 periods: when some lines are present(purple)  and a quiet period(blue}
  • 2024-04-07-19h41m00-UTC:  FFTTime plot
  • 2024-04-09-20h43m00-UTC:  FFTTime plot
    • this FFT plot compare the ASD  of the related channels (Audio and sample) for 2 periods: when some lines are present(purple)  and a quiet period(blue}
  • 2024-04-14-10h52m00-UTC:  FFTTime plot :
    • During the OMC temperature scan, there is a period (blue rectangle) where the lines amplitude increases in the SDB2_B1s_PD1_Audio channels and appears in the  SDB2_B1_PD3_Audio channel
    • this FFT plot compare the ASD  of the related channels (Audio and sample) for 2 periods: when some lines are present(purple) and a quiet period(blue}
  • 2024-04-16-00h09m00-UTC: FFTTime plot
    • same statement for the blue rectangle as the previous event
  • 2024-04-17-03h40m40-UTC: FFTTime  plot
    • same statement for the blue rectangle as the previous event
  • From all these plots it seems that
    • there is a noisy time period (purple rectangle) when the OMC shutter is opened . This time period has increased with the time  and seems to start to reduce (see last event)
    • when the noisy time period is long, during the OMC temperature scan  a more noisy period occurs (blue rectangle

• unsuccessfull OMC lock
  • 2024-04-16-21h24m20-UTC: FFTTime plot
    • the noise does not disappear but seems to increase according to the OMC temperature analysis (blue rectangle) to remain when the OMC is locked
    • this FFT plot and its zoom compare the ASD  of the related channels (Audio and sample) for 2 periods: at the beginning when the OMC shutter is opened (purple) and when the OMC is locked with B1_PD3 (blue) : the noise has increased when the OMC is locked with B1_PD3
  • 2024-04-17-00h14m00-UTC: FFTTime plot
  • For reasons unknown today, the noise present when opening the OMC shutter does not disappear and moreover increases triggering the unlocking of the OMC

For debugging purposes, the channels Audio and DC related to the B1_PD3 and B1s_PD1 photodiodes acquired at 100KHz are now stored with the "_FS" suffix and available in the RAW_FULL stream .

• operations complete at 2024-04-17-15h25m26-UTC

Below the list of the channels, acquired by the SDB2_DBOX_RightDown - SDB2_MezzPD2  mezzanines at 100KHz and stored with the  "_FS" suffix:

 V1:SDB2_B1_PD3_Audio_raw_FS              nData= 100000 min= -6.11e+03  mean=-4.89e+03  max=-3.56e+03 rate= 100000Hz
 V1:SDB2_B1_PD3_DC_raw_FS                 nData= 100000 min= -3.55e+03  mean=-3.31e+03  max=-3.07e+03 rate= 100000Hz
 V1:SDB2_B1sP_PD1_Audio_raw_FS            nData= 100000 min= -2.69e+05  mean=-2.67e+05  max=-2.65e+05 rate= 100000Hz
 V1:SDB2_B1sP_PD1_DC_raw_FS               nData= 100000 min= -3.62e+03  mean=-3.38e+03  max=-3.14e+03 rate= 100000Hz
 V1:SDB2_B1s_PD1_Audio_raw_FS             nData= 100000 min=  6.12e+04  mean=  6.2e+04  max= 6.28e+04 rate= 100000Hz
 V1:SDB2_B1s_PD1_DC_raw_FS                nData= 100000 min=  1.54e+04  mean= 1.57e+04  max=  1.6e+04 rate= 100000Hz

While investigating the problem with the lock in DC readout, we noticed that the B1_PD3 audio channel was much noisier than usual for all frequencies above 100 Hz, and also the OMC PZT correction spectrum was much noisier. We also noticed that the power on the carrier TEM00 was lower than expected for a DARM offset of -0.20.

Then, without doing anything, we observed a sudden transient at 21h40 utc that made this excess noise disappear and the B1_PD3_DC power getting back to normal.

The attached figures are comparing the B1_PD3 and OMC corrections spectrum with the excess noise (in purple) and the situation right after the noise disappeared (blue).

It was then possible to relock in DC readout while keeping the same parameters as usual for the transition to DC readout.

This strange excess noise will be further investigated tomorrow.

We investigated the issues concerning DET_MAIN, which were reported in : https://logbook.virgo-gw.eu/virgo/?r=63964

During the night from April 14 to 15, DET_MAIN went to the UNKNOWN state after an ITF unlock. This happened two times, but the two events were actually uncorrelated.

The first time, at 22h57 utc, DET_MAIN went to the UNKNOWN state because of a failure of the injection system. As shown on Fig.1, the injected power (INJ_IMC_TRA_DC) falls to 0, while DET_MAIN was in the state SHUTTER_CHECK_OPEN checking for the shutter to be opened. Since there is no power due to the failure of the injection system, DET_MAIN is not able to recognize that the shutter is open and therefore goes to the UNKNOWN state. In this situation, putting the ITF in NI single bounce, and then requesting the DET_MAIN state "FORCE_CHECK_OPEN" would normally allow to unblock DET_MAIN (then the standard state SHUTTER CLOSED can be retored).

The second time, at 00h14 utc, the shutter has been closed, but the check that the shutter is actually closed (in the state SHUTTER_CHECK_CLOSED) fails (Fig.2 and Fig.3). This is almost certainly due to the fact that around 00h14m17 the power on B1p_PD2_DC is close to zero due to interference fringes. Therefore, as there is not enough power on the dark fringe beam, DET_MAIN is not enabled to confirm that the OMC shutter is open. In this situation, requesting with DET_MAIN the state "FORCE_CHECK_CLOSED" would probably allow to recover the standard state "SHUTTER CLOSED".

This morning, we updated the conditions on the DMS flags for the QPD_B1p/B2/B5/B4 in the configuration file of the DetMoni process.

Main novelties are:

• we are now always checking the level of corrections applied to the galvos. If the corrections exceed 9V in absolute value this will trigger a red flag, if they exceed 5V this will trigger a yellow flag.
• Most of checks on the QPD signals were performed after CARM NULL 1F. We updated the logic to start performing all the checks from LOCKING_ARMS_BEAT_DRMI_1F (when the galvo loops are actually engaged).

Activity concluded at 8h43 utc.

This morning I updated the values of the SNEB_LC angular setpoints (TX,TY) in the SNEB_LC configuration file. The motivation was to reduce the offsets needed for the drift control and restore a green flag on the DMS for SNEB_LC.

The angular setpoints were changed as described below:

SNEB_LC_TX_set: from -656 to -633

SNEB_LC_TY_set: from -254 to -258

External configuration file reloaded at 07h13m18-UTC.

At 7h28 utc, we lowered the OMC locking threshold on SDB1_B1x_DC_DARM_norm_prod from 1600 to 1000 in order to make the OMC lock more robust againts ITF misalignments.

Concerning the failed OMC lock attempt around 4:00, the issue was due to the fact that the TEM00 power was too small to reach the threshold triggering the OMC lock (see Fig.1). This observation and the fact that the dark fringe was larger than during the previous successful lock (Fig.2) suggests a problem of alignment in the interferometer.

Looking at a longer trend (Fig.3), I noticed that after the earthquake the SR_MAR_TX position is following a trend with a bigger slope. Could this be indicative of an issue ? To be confirmed by ISC experts.

DET_MAIN node has been reloaded at 14h17 utc.

We have investigated the reason why DET_MAIN got stuck in the state SHUTTER_CHECK_CLOSED on April 04, as reported in this operator entry:

https://logbook.virgo-gw.eu/virgo/?r=63848

The attached figures helps understanding the sequence that lead to this situation.

After the ITF unlocked from Low Noise 2, DET_MAIN goes to DOWN, then B1p_ENABLE, then SHUTTER_CHECK_CLOSED, which is the expected sequence.

The problem happens while DET_MAIN is in SHUTTER_CHECK_CLOSED, and trying to activate the B1s and B1_PD3 photodiodes. Unfortunately, at the same time as the B1s shutter is being opened, there is a power flash on the dark fringe (B1p is exceeding 1.2 W), and the current monitored by B1s_PD1_IBias is getting close to the saturation limit (40 mA), which is probably the reason why the safety is triggered and the Vbias of the photodiode is being switched off (and then the shutter closed back).

The consequence of this event is that DET_MAIN is stuck in a state where it is waiting for the B1s photodiode to be enabled, but it never happens because the previous attempt of activating the photodiode failed.

We have now added a notification in DET_MAIN to alert the operator in case a similar event happens again. If DET_MAIN gets stuck in the state SHUTTER_CHECK_CLOSED, it will display the following message:

"WARNING: B1s_PD1 or B1_PD3 not enabled, human action required"

This message indicates that a manual intervention is needed to activate the B1s_PD1 or B1_PD3 photodiodes (Vbias to be enabled and shutter to be opened). Instructions for the operators are going to be updated accordingly.

In order to account for this modification, DET_MAIN node is going to be reloaded by the operator at the next unlock.

The attached figure shows the lock and the scan of the OMC performed in single bounce during the maintenance.

As it already happened last week, the OMC is strongly misaligned because the zero offsets for the B5 QD2 quadrant are not appropriate any more. This measurement should now be performed with the offsets recommended for the single bounce operations (values commented in the configuration file - see attached screen shot). Instructions for the operators are going to be updated accordingly.