Beatrice called me at around 3.40 LT because of the change of state of WI CO2 laser.

To restore the standard condition, I adjusted the WI chiller set point from 19.05 degrees to 19.06 degrees (2.06 UTC). The BCK chiller set point has been chaged accordingly.

After this action, power levels seemed restored (2.30 UTC). Soon after, a small adjustment of waveplate rotation was done to also recover the DAS OUT power readings on the CH PICKOFF channel (2.44 UTC).

Following the CO2 power scan done by the operator (see entry 64186), I just slightly tuned the CH powers to restore default. The action concluded at 10.03 UTC.

The goal of the shift was to perform some noise injections on the CO2 lasers by using their piezo (no need for access to the CO2 benches).

Using the calibrations performed during the maintenance [entry 63258], Matteo calculated the amplitude needed to observe in hrec the sinusoidal signal injected at 29 Hz, 68 and 85 Hz following the model reported in VIR-0911A-19. Note that the model is based on the superposition integral between the YAG and the DAS design profile but using the current applied powers. 

WI

For the WI, the voltage needs to be set on the piezo to measure 10^20 1/sqrt (Hz)) at 29 Hz is 0.006 V. A first injection has been done (at 17.25.20 GPS 1392053138, 300s )) but nothing appeared on hrec. Thus, a subsequent attempt has been done by increasing the voltage up to 0.02 V (the maximum allowed voltage to not saturate the ISSIN signal) but the line didn't appear in the sensitivity curve.

In the table below, the main parameters of the injection are reported.

NI 

For the NI,  the model predicts that with 4 V applied to the piezo, the expected values in hrec are  2.4*10^-21 1/sqrt(Hz)) at 29 Hz, 1*10^-21 1/sqrt(Hz) at 68 Hz and 8.7*10^-22 1/sqrt(Hz) at 85 Hz, to be compared with the measured ones reported in the table below. The measured values are lower by factor ~ 2 wrt the theoretical one. 

18.53 UTC: manual unlock

19.43 UTC: ITF in LN2

We repeated the noise injection on the NI at 85 Hz in LN2.

Unexpectedly in LN2 (with SR aligned), the line amplitude is lower wrt the configuration with SR mirror misaligned also in DARM (see fig.1) [ blue: SR aligned, purple SR misaligned].

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Once completed the noise injections, in agremeent with Fiodor, a common step has been applied on the ETM RH by increasing their power by 1.5 W.

To date:

NE: P_NE= 3.6W [ V=11.57 V]
WE : P_WE=4.55 W [ V=13.01 V]

At 20.07 UTC, the RH powers have been changed in:

NE: P_NE= 3.6W+1.5= 5.1 W [ V= 13.78 V]

WE : P_WE=4.55 W+1.5= 6.05 W [ V=15.00 V]

Yesterday morning, we performed some preliminary tests in preparation for the CO2 noise injection. 

As the first step, we injected a triangular wave with long period (20 s) to look at the DC gain of the conversion Piezo voltage/laser power, and to find a suitable linear response region

WI 

Amplitude : 0.1 V

Period: 20 s

We injected the trangular signal in the time interval: 09.34.50 UTC-09.36.50 UTC (see fig.1)

The laser power vs noise signal  is shown in fig. 2.

We did a similar injection on NI laser, but nothing was visible in the photodiode (ISSIN) or in the beam sampler (PRWLAS). However, after a series of checks done directly in tcs room by Beatrice, such as:

-check the status of the CO2 laser piezos

-check the cabling between the Piezo Driver and the CO2 benches,

no malfunctioning have been identified. Finally, we have found that the piezo effective gain is much lower than for WI laser. Thus, by injecting larger signal we were able to see the effect also on the NI laser.

NI 

Amplitude : 4 V

Period: 20 s

We injected the triangular signal in the time range:  10.33.54 UTC-10.35.54 UTC (see fig.3)

The laser power vs noise signal is shown in fig. 4.

To conclude, we need to proceed with a calibration of the piezo, both in amplitude and in frequency:

-apply the sinusoidal signal to the piezo at fixed amplitude for different frequencies

-apply sinusoidal signal to the piezo at fixed frequency for different amplitudes and measure corresponding signal on the photodiode.

This morning, profiting of the maintenance, I went to the TCS room to check the status of the cabling of the piezo driver in order to implement the DC power stabilization of both NI & WI CO2 lasers. Some pictures have been taken:

Fig.1: piezo driver, frontal view

Fig 2: the two cables shown in fig.1 are connected to the DAQ box 31 (channels 0 and 1).

Fig.3 Piezo driver, back view. The two cables shown in this figure are connected to the NI and WI laser benches.

Thus, from the cabling point of view, everything is fine.

The nominal and measured CO2 powers are collected in the table below:

All the powers have been reset to the nominal ones.

All flip mirrors have been re-opened at 07.32 UTC.

Since June 5th at around 15 LT, the WI CO2 main laser temperature no longer settles on the chiller set point temperature (see fig.1).

To investigate the issue, we tried to change the chiller set point temperature by increasing it but the problem persisted (see fig.2):

• June 6th: 13.57 UTC: 19.00 → 19.10 degree

• June 11th 19.36 UTC: 19.10 → 19.15 degree

One hypothesis to explain this anomalous behavior is a malfunctioning of the chiller, thus, this morning we performed a test swapping the WI chiller with the back up one.

The operation has been done at 8.55 LT (fig.3).

The test will go on all day. 

Practial info:

1) yesterday the back up chiller temprature set point has been changed accordingly to the WI one (i.e 19.15 degree)

2) during the swapping of this morning, the pump speed of the back up chiller has been set from MEDIUM to HIGH and, at the same time, the pump speed of the WI chiller has been set from HIGH to MEDIUM.

Today afternoon, the PA actuator has been moved from the TCS room to its final position on the NI tower base.

Monday, the electrical cabling will be performed.

This morning, the WI CO2 bench has been opened to replace the power reader of the WI DAS outer ring, out of service after the blackout and to replace the WI saturating thermal camera with the spare one (fig.1).

After replacing the camera:

• the proper connection to the camera has been checked following the standard  procedure

• the framing and focus of the camera on the cardboard have been adjusted.

An image of the DAS has been acquired with the outer ring at higher power wrt the nominal one (fig.2). 

The thermal camera images have been re-analyzed to identify some difference in shape/power distribution between and after the power jump of yesterday morning.
Three different set of DAS outer ring  images have been analyzed:

1. 9th May before the blackout

2. 19th May after the blackout

3. 30th May after the laser power jump

The outer ring images in the three different sets are shown in fig.1 . The RMS difference between the two normalized images have been calculated for set 1 and 2 considering it as a reference to evaluate possible changes between/after the jump . 
The same analysis has been applied to the images of set 2 and 3. In the first considered case, the RMS difference  is 0.049 and between/after the laser jump is 0.039. Thus, no significant changes are observed in the WI DAS. 
Although IR camera images cannot be directly used to derive the intensity profiles of DAS Rings on CP, they can be efficiently used to look at changes in these profiles.

This morning we noticed a jump in the WI CO2 laser power triggered by the laser temperature change (see fig.1).

The laser stabilized in a new point, so the CO2 powers have been checked by switching off one actuator at time and reset to the nominal ones.

The operation has been completed at around 10.50 UTC. We will keep monitoring the laser behaviour in the next hours.

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During the morning, Andrea acquired the thermal camera images of the CO2 actuators.

Thermal camera images acquired today have been compared with the ones acquired on 19th May (60259).
The CH+DAS OUT images on both dates are shown in Fig.2 and Fig.3 for the WI and NI with their cross-correlations, respectively.

The results are summarized below. 

WI
Displacement results in pixels: X=0.9+-1.0, Y=-0.4+-1.0 .
Displacement results in mm: X=1.4+-1.5, Y=-0.5+-1.5 .

NI
Displacement results in pixels: X=-0.5+-1.0, Y=0.3+-1.0 .
Displacement results in mm: X=-0.76+-1.70, Y=0.52+-1.70 .

It comes out that the DAS and CH position did not change on the CP.

At 15.02 UTC, the WI DAS+CH beams have been displaced vertically 0.5 cm acting on the WI HM TX by 2278 steps backward, with ITF in LOW NOISE 2 since roughly 30 minutes.

A set of images of CO2 actuators on both benches has been recorded today with the diagnostic system cameras. Images were taken since 15.26 LT. Tiff and csv files will be transferred tomorrow to the dedicated folder in data/tcs/buffer/Optris_Images/230411/NI and WI.

Profiting of the unlock, in the time interval 17.55 UTC-18.30 UTC,  the CH powers have been changed accordingly to the DAS ones. We also checked all CO2 actuator powers by switching off them one by one.

The new powers, CH and DAS,  injected into the ITF are summarized in the table below.

Today, in order to test the effect of a DAS differential tuning on the sideband overlap on B1p phase camera, we changed the power on NI DAS by +5% and on WI DAS by the same amount with the ITF in low noise 1. The power change started at 13.47 UTC and was completed at 14.07 UTC. However, inadvertently, we changed the NI OUT power by a too large amount (10% instead of 5%). The correct change (+5%) was reset at 15.13 UTC. New powers are summarized in the following table.

The ITF is left locked in low noise 1. In case of unlock, we will change the CH powers as well to ease the lock acquisition.

At around 15.00 LT, Claudia acquired the thermal camera images of the CO2 actuators (see fig.1 and fig.2 for the WI and NI, respectively). 

All images are available in /data/tcs/buffer/Optris_Images.

The CH+DAS OUT images acquired on 31st March have been compared with the ones acquired on 28th March during the maintenance (59473) for both NI and WI.

For the WI, the CH+DAS images are shown in fig.3 and the cross-correlation in fig.4.

We obtained: 

• Displacement results in pixels: X=0.5+-1, Y=0.1+-1 .
• Displacement results in mm: X=0.8+-1.5, Y=0.2+-1.5 

Concerning the NI, the CH+DAS images are shown in fig.5 and the cross-correlation in fig.6.

• Displacement results in pixels: X=-0.6+-1.0, Y=0.1+-1.0 .
• Displacement results in mm: X=-0.9+-1.5, Y=0.1+-1.5.

It comes out that the DAS and CH position did not change on both CPs.

This morning the TCS maintenance activities have been done:

1) thermal camera images to monitor the CO2 actuators (see fig.1 for NI and fig.2 for WI)

All the .tiff and -csv pictures are in data/tcs/buffer/OptrisImages/XX/230328/

 XX  is NI or WI

2)  power checks by turning off CO2 actuators one by one 

The actions have been completed at 12.00 UTC.

The analysis was done using the HWS DET data taken on March 10th, starting at 18.25 LT (see entry 59214). NI and BS mirrors were tilted by a fixed amount (5 urad) and the effect on HWS DET tilts was observed. Fig.1 reports angular signals on BS and NI during the HWS acquisition. On running CallPistTilt code to get the HWS tilt contributions, [RMS, TiltX, TiltY, time] = Call_PistTilt(30,'file','./DET/20230310T1825/Wavefront/',1,38), I found the curves shown in fig.2. 

According to the plot, once we take the average value over 5 WFs, the conversion matrix is:

The formulae for HWS DET tilts are therefore:

Tx_HWS = 6.2*NI_Ty - 33.3*BS_Tx

Ty_HWS = 6.9*NI_Tx - 43.6*BS_Tx

Taking into account the fact that CallPistTilt divides the WFs by 2 (since it is meant to deal with double pass measurements), the actual tilt gain from NI to HWS is pretty close to the magnification (~13), as expected.

Notice that apparently we do not see any effect from BS_Ty. This corresponds to WFs such as the one in fig. 3. A deeper investigation will follow.

We started to relock the interferometer at 20:04:53 UTC.

We reached CARM_NULL_1F at 21:20:47 UTC, here a few remarks:

• we locked ALS in the usual way, after the software upgrade; after one unlock the first time we tried the handoff to the beating signals (20:16:28 UTC), no issues were observed;
• the DRMI was quite difficult to relock, it usually needed the SR TX+ misalignment to speed it up;
• we had to retune the PRCL gain in the three STEPs of the lock acquisition, and CARM_NULL_3F, as it was quite high;
• we observed the announced variations in the IMC transmitted power, quite well reproduced by B4_DC and B7/B8_DC (Figure 1);
• having a OS target = 0.5 Hz we were often crossing 0, also with very high SRCL_SET ~= 22; we increased the setpoint to 4 Hz with some effects, with SRCL_SET again oscillating at low frequency;
• also the SR alignment, especially on TX, was not stable, oscillating at around 3 mHz (Figure 2); we tried to check and improve the loops but we did not spend much time on it after reaching the thermalization, in order to allow the TCS activity;
• BS_TX was basically mimicking SR_TX;
• we unlocked at 22:36:55 UTC (the lock lasted 1h16m), during the preliminary TCS activities.

We left the ITF configured as during this lock, but some time should be devoted into a more careful check on the SRC conditions.

During the writing of the entry and the discussion on the actual feasibility of the TCS activity (it was decided to postpone it) we collected other unlocks: one at CARM_NULL_3F (120 Hz on DARM, 22:49:41 UTC), more than one of ALS (22:53:37 UTC, etc.). We changed the thresholds on ALS_WARM.

Once the activity in the INJ lab finished around 20.00 UTC, ISC team started the relock of the ITF (59255). CARM_NULL_1F was reached at 21:20 UTC, but the lock did not seem really stable.

Before performing any action on DAS powers, we preferred to check their status.

At about 22.45 UTC the values as seen by the CO2 PICKOFFs were in pretty good agreement with the reference settings:

The DAS differential tuning activity is postponed to tomorrow morning shift.

The goal of the shift is to measure how much the DAS and the CH compensate each other.

14.05 UTC all NI CO2 actuators closed, and NI DAS powers set to only compensate the NI CP cold lens, as reported in the table below:

17.11 UTC ITF put in single bounce NI and NE and WI misaligned by ~ 20 urad TY.

We decided to spend some time in a calibration of the tilt signal of the HWS by tilting the North ITM and the BS.

17:25 UTC HWS-DET acquisition started (/data/tcs/buffer/HWS-RC/DET/20230310T1825/).

17.46 UTC HWS DET acquisition stopped.

17.47 UTC NI CH flip mirror closed (it was opened by the automation at 17:15 UTC).

19:14 UTC new HWS-DET acquisition started to make the CH-DAS measurement. (/data/tcs/buffer/HWS-RC/DET/20230310T2014).

19:25 UTC NI CH flip mirror open, with about 80 mW in the CH beam.

21:10 UTC NI DAS power increased to standard values:

• INNER: 295 mW
• OUTER: 3.15 W

23:23 UTC HWS measurement still ongoing, will stop by itself at around 3:00 UTC.

Figure 1 shows NON-Gaussian weighted curvature and RMS measured so far on the HWS (not projected on the ITM). A deeper analysis will follow.

Today at 10.15 UTC we checked the set of powers of the CO2 actuators on CPs, performing some small adjustment of the readings to the nominal values. Measured values are summarized in the following table:

All values were reset to nominal.

Soon after the activity reported in 59194, electronic crew went to the CO2 benches to replace the flip mirrors cables.
Now the flip mirrors can be opened/closed from the TCS room. In this occasion, the NI DAS and CH thermal camera images have been acquired after the movements performed this morning (59194).

The DAS images acquired today are shown in the attached fugure. 

To be compared with the images reported in 59182.

Today we took a set of images of the TCS CO2 actuators using the thermal cameras installed on the benches (see entry ). The images  are meant as a reference for future steering of actuators. 

Taking the snapshots required a direct access to the benches due to the fact that we are not able at the moment to flip the dianostic system mirrors remotely. However, the benches have been opened for a short time in the least invasive manner we could. The flips have been operated using the button on top of the flip body. The enclosures of both benches have been closed immediately after the images were taken. Figure 1 shows the pictures of the NI actuators (taken at around 14.30 LT), while figure 2 shows the same for the WI bench (at about 15.00 LT). Images are also saved as temperature profiles.

The quick access offered also the possibility to directly test the remote connection of the diagnostic system flip mirror on the WI bench, that in the past tests seemed insensitive to attempt to flip from the TCS room with the supplied remote button (that was instead successful for the NI flip). The tests suggested the problem is in a bad electrical contact of the SMA/jack adapter temporarily installed to connect the flip to the cable. The adapter has been removed to perform further checks.