Here below the instructions for the cavities locking

Preliminary steps

• Open a terminal
• go in the folder wich contains the two scripts by typing: "cd /olusers/virgorun/ISC/LSC"
• start ipython

Run of the locking scripts

• for the North Arm type "run narm _lock.py"
• for the West Arm type "run warm_lock.py"

Then you acces to the following functions:

• {N or W}ARMlock() to lock the arm
• {N or W}ARMunlock() to unlock the arm
• {N or W}ARMdrift_ctrl(1) to switch on the drift control
• {N or W}ARMdrift_ctrl(0) to switch off the drift control
• {N or W}ARMhandoffB4() to pass from the lock in transmission to the lock in reflection

To lock the cavity in transmission:

1. {N or W}ARMlock()
2. {N or W}ARMdrift_ctrl(1)

To pass from the lock in trasmission to the lock in reflection

1. {N or W}ARMhandoffB4() with the cavity locked in trnsmission

To unlock the cavity (either from the lock in transmission or reflection)

1. {N or W}ARMunlock()

Note that: to simplify the things today I renamed the functions in order to be coherent between the two arms. I tested only the script of the North arm, I could not test the script for the west arm because there was an ALS acrivity

Below the list of the activities communicated in control room:

- SQZ cabling inside the detection lab (in progress);

 - ALS alignment by Matteo, Raffaele and Romain (in progress);

- mechanical works around SQZ area by LAPP team (in progress);

Today, I covered the WI CH CO2 bench with a pellicle layer as a temporary solution to protect the optics from the dust.

The final plexiglass cover will be installed in a few weeks.

it seems the unlock of PSL/IMC has been triggered by the mechanical resonnance of the PMC piezo.

Plot 1 PMCREF_I features a quiet period then a noisy period which ends with a large glitch which causes the unlock.

plot 3 is a zoom which shows a preliminary glitch before the large one

plot 2 is a zoom of the preliminary glitch:

we see the EOM_CORR is ~ 0,2 Vpp, that is 120 Vpp on the crystal (the PA83 amplifier which drives the crystal is limited to 120 V). It means 120 V * 9mrad/V = 1,08 rad pp at 9 kHz, this is a frequency variation of 9,7 kHz

the PMC error signal sees ~1 V pp (according to a 1.5 Vpp Error signal and a PMC pole of 781 kHz. This would mean

that either the frequency of the laser is sweeping by 520 kHz (this is not visible on the ML_PZT nor on the ML_FREQ_I_MONIT) or that the PMC is shaked around the laser frequency.

If the latter the doppler effect on the transmitted beam is a phase mdulation of pi/781kHz*520 kHz = 2 rad_pp at 9 kHz, this is 18 kHz.

The 18 kHz are managed by the IMC loop and would give rise to 9 kHz on the EOM and 9 kHz on the ML_pzt ( 1 mVpp * 10 * 1.2 MHz/V = 12 kHz).

Therefore it seems the PMC is shaked around the ML frequency due to some instability in t e PMC loop.

9 kHz is close to the mechanical resonnance of th ePMC piezo. It would worth to measure the PMC OLTF and check that the electronical compensation of the resonnance is still well tuned.

The two spectrograms compare seismic noise in the range 46 to 50Hz at NEB and WEB between March and now. Figure 1 is refers to March, Figure 2 is now.

We notice:

• NEB: a significant reduction of the intermittent noise associated to the Boiler (consequent to springs installation). There is still a small residual.
• NEB: the intermittent (faint) noise from the chiller is no more visible (no intervention done)
• NEB: the water pump noise is probably still there (but we need a switch off to certify that the line at 48Hz is effectively the water pump)
• WEB: the intermittent noise associated to the Boiler is no more visible (consequent to springs intallation)
• WEB: the intermittent noise assocated to the chilleris still visible, but is seems associated to just one of the tw chillers....
• WEB: the water pump noise is reduced (consequent to replacement of noisy pump).

State of Virgo: Unlocked.

ITF Mode: Upgrading.

Quick Summary: IMC locked; SWEB & SNEB in-air, SDB2 loops open; all suspensions loops closed; SR-BS Valve close; TCS CO2 lasers off; INJ_MAIN in pause, all the other automation nodes OFF.

Activities ongoing since this morning: mechanical works around SQZ area by LAPP team.

Today we tried to improve without success the alignment of the north arm. At the end of the process we realized that the angular position of the bench was different respect to the one used in the last lock (28th septemer). 

We moved the bench in the position of the 28th septemer and  we realized that between the old configuration and the new configuration appeared higher peaks. Moreover observing the SNEB_B7_Cam1 we restarted to see a beam. Thus we select a SNEB angular position with the beam centerd in the camera and we restarted to have transmission peaks with the usual height (about 0.2mW) figure1. At that point we locked the arm without problem using the narm_lock.py script.

Today we passed part of the SVS cables, starting with the ones for the AEI squeezer, from EE room to DET lab clean area. The work will be continued tomorrow.

Since yesterday afternoon the particle counter in DET lab has been moved inside the new clean area on a temporary position to monitor the dust contamination during QNR installations.

see 46557

ML_DC_Monit_FS monitors the ML power before the long fiber

Figure 1 shows that during the time when PMC only was locked (IMC unlocked) the increase in noise in the PMC channels corresponded also to an increase in noise in the master laser DC monitor (but not in the frequency monitors). 

Figure 2 and 3 if you compare the normalized spectrogram of the PMC error signal and of the master laser DC monitor, the increase in noise happen at the same times. So clearly they have a common origin.

This raises two questions:

• What is exactly the sensor for the PSL_ML_DC_MONIT_FS channel, and where is that sensor located in the optical path?
• Is there any feedback applied to the master laser in this configuration (PMC locked, IMC locked)?

If there is no feedback applied, then it points to the master laser as the origin of the problem (or whatever that is between the master laser and the ML DC monitor). Or that the electronics that are providing the feedback are creating their own time varying noise, which could be tested by physically unplugging the cables from the master laser.

while trying to understand the 49632

I have noticed that the PMC seems quite misaligned.

~ 6 % in the TEM01 mode. It is worth to realign it since it makes the PMC more sensitive to any coupling

Here it will be described the procedure applied to reach a lockable arm starting from 'no flash' state.

First of all, the mirrors (BS, WI, WE) have been placed at the same values recorded by the optical levers at the time of the latest 'flashing' state. One can find the good gps plotting the trend of the channel SWEB_B8_DC_max.

In the table: the values at the good gps; the current values at the beginning of the alignment; the additional offset to apply to the LC set points. N.B: inserting the good recorded values as new set points in the DSP cards does't work, because those numbers are not the only offsets. There are also the offsets added by the automatic alignment system, recorded in internal variables. One has to add the difference between the current and the requested values of the signals in the data, and check that the signals at the end are correct.

During the restoring of the old position, a first flash was seen (fig 1). At this point, the normal procedure of random search of higher flashes started. In order to be more efficient, it can be useful to look at the image of flashes on the camera. Also looking at the reflection of the input mirror on B4 camera could be useful: it should be not far from the center. But also a 'blind' search, as I did yesterday, usually can easily lead to improve the flashes at least up to 0.1 on SWEB_B8_DC. Since I was not able to do that, I asked to do a scan of SWEB position. The result was the desired one: flashes of more than 0.1 were obtained (fig 2).

At this point, the information from WE camera was talking about a vertical misalignment. The flashes were still maybe too low to be locked, so a further attempt to improve the cavity alignment was done. Unfortunately, from this condition the adjustment of a single mirror never works: any single change leads to a lowering of the flashes. Any possible improvement needs always a combination of motions. The possibilities are two:

1) the beam direction is correct, but the optical axis is shifted;

2) the beam is pointing out of the END mirror center.

In the first case, a combination of IN and END mirror adjustment is needed (even up to several urad for both). In the second case,  all the three mirrors has to be moved (up to several urad too).

Yesterday I tried a different vertical orientation of the beam (BS_TX), the amplitude of the flashes was doubled, but a further step did not give any improvement (fig 3). The flashes were high enough to try a lock, and in fact the lock was acquired and the automatic alignment made the final step: BS_TX was put back to the position before the step of fig 3 (which was evidently a wrong choice), and a shift of the optical axis was performed (fig 4).

Below the list of the today's activities:

- mechanical works around SQZ area by LAPP team (in progress);
- ALS alignment on SWEB by Matteo, Raffaele and Romain (in progress);
- SQZ cabling inside the detection lab (in progress);

Electricity
from 12:23UTC to 15:10UTC we ran under diesel generator because of a failure from the electricity company, now the situation is back to the normal working condition.

SUSP
At 6:49UTC & 9:20UTC the WI local control had been opened by the guardian, controls closed.

Yesterday during the activity described in log 49700 we had the occasion to test some noise feature of the 4-channel power supply module (PCB mod,482C05).

The module we tested is located at NEB (ENV rack) and it is currently used to power the meggit accelerometer on the ALS bench, channel ENV_NE_ALS_ACC_Z.

We had another meggit accelerometer that we positioned (vertically oriented) on the floor next to the Guralp (see this image).  In this location the seismic noise is farily quiet.

At first we powered the meggit accelerometer with a battery-powered 1-ch power supply (PCB model 480E09), and obtained a seismic spectrum that matches well with the nearby Guralp: see Figure 1, where channel ENV_NEB_ACC_V is our meggit sensor, while ENV_NEB_SEIS_V is the Guralp velocimeter vertical channel.

Then, we powered the same meggit sensor on the 4-channel power supply module, and the spectrum changed significantly: some new structures appeared with significantly larger level. These structures are similar and coherent with the noise measured by the accelerometer on ALS bench. The structures in the meggit accelerometer are a factor of 10-20 smaller than the ALS accelerometer. This is shown in Figure 2: the blue line is the ALS accelerometer, in orange is our meggit placed next to the Guralp in the pit

Finally, to check that the noise measured by the ALS accelerometer can be trusted as real seism, we powered the ALS accelerometer with the trustable 1-ch battery power supply, and the signal remained the same, except for the 50Hz harmonics that disappeared. This is illustrated in Figure 3.

Concluding:

• there is a noise cross-talk among the 4-channels of the PCB mod.482C05. This cross talk is at the level of 5-10% and seems large with respect to the max. cross talk declared by the vendor (-72 dB --> 0.025 %)
• we have to check if this is a problem of just this NEB module (by the way, recently purchased)
• this power supply has also adds a noise at 50Hz and harmonics (this was already studied in elog 48478 - for the wilkoxon power supply - and attributed to the non differential output).

Yesterday after the realignment of the WEST arm made by Paolo and Julia we tried to lock the WEST arm in trasmission using the B8 photodiode.

At the first lock attempt we opened the controls of the WI. Then we relized that something was wrong:

the two signals LSC_Warm_ENBL and LSC_Warm_TRIG were allways high (see fig 1)  regardless of the height of the peaks. 

We tried for half an hour to solve the problem without succes. To solve it fastly we tried to restart the ISC_Lsc process.

After the restart the trigger worked properly again and we managed to lock the cavity before in transmission and then in reflection. When we unlocked the cavity at the end of the ALS activity the two triggers remained high.

This morning we investigated agian the issue and we realized that in the script warm_lock.py:

1. the function HandoffB4() disables the two triggers for the guided lock 
2. the unlock function did not restore them

To solve the problem I added the following lines in the unlock function

    LSC.B8_GL_DC_TRIG_HI = -2
    LSC.B8_GL_DC_TRIG_LO = -2

Might be worth to measure the PMC OLTF to check it is still well adjusted together with the mechanical resonnance compensating electronic filter.

Yesterday we performed some tests on the Guralp sensor at the NE building.

These tests were triggered by Paolo. He observed that the seismic noise detected by the NEB guralp sensor worsened and changed since December 2019 till the end of the O3 run and never recovered to the "good level" measured in April 2019. The seismic noise worsening/changes occurs above ~30Hz, and specifically they happened on Tuesdays, the  Dec 10, Jan 14, Feb 11, and March 17. This analysis is illustrated in the first attached document.

We first suspected the LN2 truck going to NEB every two weeks for refilling the external tank. But, the arrival and departure times of the truck, that  are clearly identifiable in the suspension signals, demonstrate that the truck already left NEB when the noise in the Guralp arose.

Note the guralp sensor is placed in a corner of the tower pit floor, covered by an insulating box. See the attached picture.

First, we did  an Huddle test putting one meggit accelerometer at 1m distance from the Guralp sensor (see the picture). We trust the meggit accelerometer to have a flat acceleration response from a few Hz to some hundred Hz. We measured a transfer function between the two sensors along the three directions, orienting the meggit in turn along the vertical, then N, then W, using one viton cube support.  These TF are reported in figures 2, 3 and 4 respectively for the vertical, North and West axis.

The vertical TF looks fairly smooth up to 100Hz. The North and West axis TFs instead start losing coherence above 50Hz. This is associated to excess noise in the Guralp signal, evidenced by the red curve in Figures 3 and 4.

secondly, we checked what happens to the Guralp signals when gently kicking the guralp box, like it might have happened during cleaning operations of the pit.

We observe that, once the signals has recovered from the transient, the quiet guralp signals above ~50Hz look quite different: some stationary spectral noise structures changed amplitude. Figures 5 and 6 (linear scale)

This might resemble what Paolo observed.

Concluding:

• We make the hypothesis that the sensor has been hit occasionally during cleaning operations during O3, each time faking a noise increase or noise change in the signals.
• ... indeed, as just found out, all the identified dates correspond to cleaning operations at NE (reported in the cleaning operation logbook https://wiki.virgo-gw.eu/Commissioning/Operations/CleanFirm)
• This might be a symptom of the sensor masses being not centered (centering the masses is not straightforward and we are working to set up the operation)
• The observed noise (ref. to Paolo attached document) are to be considered not due to a real seismic source, but just sensor noise.
• The sensor cannot be trusted above 30Hz. Indeed, the Guralp sensors specs. guarantee its operation only in the range up to 50Hz.
• We need to improve the sensor installation, in such a way to protect it from accidental kicks.

During the night of Oct 13 - Oct 14, the PMC was locked but the IMC was unlocked.

To find if the laser noise increase as it does repeatidly when the IMC is locked we cannot look at the EOM correction, as there is no correction sent with the PMC locked only. But we can look at the PMC error signal.

Figure 1 shows the trend data, and one can see that the RMS increase by about a factor of 2 for a few minutes repeadily. The increase is much less visible than when the IMC is locked, but this is just because the PMC signals is much more noisy when the IMC is not locked and the additional loop on the master laser is locked.

Figure 2 shows the PMC signals in 4 conditions

• Purple - PMC only locked and noise is low
• Brown - PMC only locked and noise is high
• Green - PMC and IMC locked and noise is low
• Brown - PMC and IMC locked and noise is high

On figure 3 and 4 I have made spectra of the PMC signal (one per minute, with log spaced frequency) and shown a spectrogram normalized by the median over time for the data for the night of Oct 13-14, where the noise elevation can be seen.

Note that this type of analysis needs to be done quickly. The high sampled data (>100kHz) remains on disk only for ~10 days.

/users/mwas/detchar/protoFastUnlock_20201013

Below, we summurize speed variations of engine driving fans for supply and return at central building:

In Fig.1, we observe a slight variation of the temperature inside the central hall (top panel) and a temperature reduction of ~0.2 degree measured by different probes when the inverter is set to 40 Hz  (middle panels).
As reported in Fig. 2 (middle panel), the inverter velocities 40 Hz and 35 Hz produce an acoustic noise reduction of a factor  ~1.4 and 1.5  with respect to nominal condition (50 Hz) in band 1-16 Hz, respectively. Regarding the acoustic RMS  in frequency band in 16-512 Hz, it  worsens at 35 Hz but it is worth to underline that other possible noise sources can fall in this band.
In the seismic spectrogram (Fig 3), we see a couple of lines changing frequency:

16.5 Hz --> 15.3 Hz -->13.5 Hz  when the inverter frequency goes from 50Hz-->45 Hz-->40 Hz

8.3 Hz-->7.5Hz-->6.7 Hz-->6 Hz  when the inverter frequency goes from 50Hz-->45 Hz-->40 Hz--> 35 Hz

The acoustic spectrogram (Fig 4) shows the hall microphone signal durin the test in the frequency  band 1-20 Hz. We observe the noise progressively reduced in  frequency bands 2-4 Hz  and 10-20 Hz. Instead, in the band 4-10 Hz the reduction of inverter speed does not always correspond to a reduction of the acoustic noise.