In case someone in the future wants to connect the opening and closing of work permits. The NI tower permit to work has been closed using an independent logbook entry https://logbook.virgo-gw.eu/virgo/?r=69393

While the IMC and the RFC were locked and the BPC was following the IMC, we tried to change the setpoints of the AA control loop. We changed the setpoints of the MCT_{h/v}_SET and {N/F}F_AC{h/v}_SET channels.
While changing the FF_ACv_SET setpoint toward negative values, there were a clear improvement RFC_TRA power, however, the Ioop became unstable because the sensing matrix changed with the setpoint.

The next figure shows the evolution of the IMC_TRA and RFC_TRA while we were changing the diffferent setpoints

After the test, we set back the RF quadrants setpoints to 0, and the setpont the end mirror quadrand to -0.1 vertical and +0.45 horizontal. Then, we tuned the INJ_IMC_SET in order to minimize the coupling with PMC.

Below the list of the activities communicated in control room:

• standard maintenance in the morning with cleaning operation of the experimental areas and CEB + MCB bridge crane maintenance;
• test on the electrical generator of the TB;
• NI payload balancing and first contact peeling;
• PAY WI intehration;
• visual inspection of NCal at WE by Benoit.

Afternoon operations:

NI tower: final cleaning, wafer positioning, flange closing (Francescon, Gargiulo, Menzione)

WI tower: payload integration (Benedetti, Majorana, Menzione, Zaza)

In this entry, we report the results of the mechanical transfer function measurements performed on the NI and WI instrumented baffles.

As a reminder, the measurement setup consisted of a triaxial accelerometer installed on the baffle in two different positions, referred to as TOP and BOTTOM, using a custom adapter.
A monoaxial reference accelerometer was sequentially installed in three locations: R1, horizontal position below the baffle; R2, vertical position close to the baffle; and R3, horizontal position on the vacuum vessel.

Due to the threaded mounting of the triaxial accelerometer, the final sensor orientation was slightly different between the TOP and BOTTOM installations and was therefore not perfectly aligned with the nominal vertical-horizontal reference frame. The only direction that can be directly compared between all measurements is the sensor axis aligned with the adapter, which is approximately perpendicular to the baffle surface:

• NI instrumented baffle
  •  top acc position--> z-axis
  • bottom acc position--> y-axis
• WI instrumented baffle
  • top acc position--> y-axis
  • bottom acc position-->z-axis 

Figures 1–12 show the comparison between the quiet and injection spectra for all the investigated configurations. The shaker excitation significantly increases the vibration level over the ambient noise background, clearly revealing the frequency bands where the mechanical resonances of the instrumented baffles are excited.
A transient is visible in the quiet acquisition of the WI BOTTOM configuration with the reference accelerometer installed below the baffle (R1), Figure 10. Despite the increased background level, the injected signal remains clearly distinguishable and does not affect the estimation of the transfer functions.

Based on these measurements, the mechanical transfer functions were estimated for all the investigated configurations. The complete datasets are provided in the attached ASCII files (*_transfer_function.txt).

Figures 13–24 show representative transfer function measurements for the sensor axis aligned with the adapter axis. The top panel compares the ASDs measured by the reference accelerometer and by the triaxial accelerometer along the selected axis. The second panel shows the coherence, while the third and fourth panels report the transfer function magnitude and phase, respectively. Red markers identify the transfer function and phase values corresponding to frequency bins with coherence > 0.4.

Candidate resonance frequencies were identified using selection criteria based on the transfer function magnitude, coherence, and phase evolution around the candidate peaks. The complete list of the identified peaks for each measurement configuration is provided in the attached ASCII files (*_candidate_modes.txt).

Today, we performed the following actions on the NCals:

• At NE:
  • At 14:46 UTC, we add the NCal_NW_5V channel which monitor the 5V for the North-West power supply.
  • We disconnect/reconnect a few time (until 15:15 UTC) the 5V cable from the back of the North-West power supply in order to remove the observed glitches on the position sensors and temperature probes. This seems to improve the situation.
• At WE, (from 3:30 to 5 pm UTC):
  •  We checked the WNN, WEN, WSN microphones. WEN, WSN were restored by plugging the cables on the DAQbox (they were disconnected for some test a while ago). Since the "East" microphones were removed long ago, the WNF microphone has been connected to replace the WEN microphone. The gains of all microphone boards have been checked to be 40 db. The offsets of the DAQ boxes configuration have been adjusted to center the signals around zero (as well for NE microphones).  
  • The temperature probes of the WEN et WWN box have been fixed by changing the connectors (the small cables are mislabeled) on the DAQbox. The corresponding gains have been checked.
• At the end, all rotors were restarted at their nominal rotation speed.

The Virgo interferometer when locked has a 100kW 1064nm beam circulating beam, which seems like a high power from which scattering can be dangerous to the eye. However that high power is only achieved thanks to the extremely low scattering of the main optics.

Viewports are located at a large viewing ange from the mirrors with angles greater than 10 degrees, the BRDF of the LIGO mirrors has been studied in detail https://arxiv.org/abs/2201.05640. With BRDF of 8e-4/theta^2 at large angles with theta in degrees, and total integrated scatter of less than 10e-6 for angles between 1 degree and 75 degree. The viewports are located at a distance of about 1.5 meters from the mirror. Hence based on the BRDF  the 1064nm laser power density at the viewports is 100e3 W * 8e-4/(10 deg)^2 / 1.5m^2 = 0.35 W/m^2, and decreasing further as in practice the closest viewports to the beam have a viewing angle of 19 degrees (photon calibrator), and most viewports are at even larger angle. 

This should be compared to the maximum permissible exposure of 50 W/m^2 for long term exposure to 1064nm light according to IEC60825. So the power density at the viewports is over 100 times below the maximum permissible exposure (MPE). 

Scattered light at large angle is due to the sum of scattering from many scattering points, the scattering may interfers coherently creating a speckle pattern where in some directions the different points add up coherently while in others the interfer destructively. The resulting random power distribution has the mean of 0.35 W/m^2 with fluctuation distributed exponentially, which means that for example the probability of having a power density 10 times higher than the mean at given point in space is exp(-10) = 4.5e-5. Thus taking into account a very improbable speckle the power density would remain more than a factor 10 below the MPE. Note however that scale of the speckle pattern should be small, for interference between two point sources located 5cm appart (size of the beam on the mirror) and viewed at 1.5m (distance to the viewport), the interference fringe spacing is 1064e-9*1.5m/5cm = 32um. Hence in practice the human eye will see the average power with microscopic variability of the power density.

The 1064nm main laser should be classified as a class 1M laser at the level of the viewports of the core optics vacuum chambers. This applies to the input and end mirrors, as well as BS and SR where the power density on the optics is orders of magnitude lower.

This property is independent of the quality of the optics, if for some reason an optic has an increased scattering, the recycling gain of the interferometer will decrease keeping the scattering power density constant. Scattering is in any case the dominant source of loss in the interferometer, hence the power conversation dictates that from 17W of input laser power, 4W is lost by scattering at each mirror of the two arm cavities. The large angle scattering from point defects can be well approximated by a uniform angular distribution, hence at the viewport the power density can be estimated as 4W /2/pi / 1.5m^2 = 0.28 W/m^2, finding again a similar value to the computation based on the BRDF. Scattering cannot increase above that value as only 17W of laser power is available at the interferometer input.

ITF in UPGRADING, DOWN

no activities reported to the control room

The following report has been submitted to the On-call interface.

On-call events -> Electricity

Title: ENEL GE1 Network Alarm

Author(s): dandrea

Details:

I received a call from the alarm system on the power grid about a lack of ENEL grid on the GE1 that powers the central building and the control building.
I intervened on the site and found the rescue generator set in operation, as it did not have the ENEL reference voltage.
A fuse had blown on the control board which I promptly replaced and the system returned to normal operation.

* Note that any files attached to this report are available in the On-call interface.

ITF found DOWN and in UPGRADING Mode.
All times are UTC.
Below the list of actiities comunicated to the Control Room.
07:08 - 07:35 PAY: NI electrical checks with payload integrated with the superattenuator, works on the platform (Gherardini, Pinto, #69369).
07:25 - 10:25 PAY: WI payload assembly in CEB Clean Room (Dicorato, Puppo, Ricci, Travasso).
13:37 - 13:57 Inspection of CEB IR Cameras (Boldrini, Spinicelli, #69375).

We surveyed the NI and WI tower to take note of possible safety issues concerning the viewports used for the PAY cameras.

We restored the position of the NI_Cam and enveloped both the camera and the viewport with a black aluminum sheet. That viewport has been secured and no light from the YAG will be able to exit the tower through it.

For the WI_Cam, the situation is a lot different (pictures 1,2). The camera is fixed on a metal bar, propped against the tower and resting directly on the SLED box. The viewport itself is completely exposed, which will be a safety concern once the YAG circulates again in the WI tower.

We'll take steps to address these concerns as soon as possible.

A comb of line spaced by 50Hz is present in the PSTAB spectrum, and the projection of those lines in the sensitivity show that the 250Hz line, and maybe some other are dominating the contribution of 50Hz harmonics to the sensitivity. The real solution will be to have fully differential calbing from the PSTAB photodiodes, instead of single ended calbing inside the vacuum as is currently the case. In the mean time, a feed forward of the 50Hz and its harmonics could be tried to reduce those lines. 

https://git.ligo.org/virgo/commissioning/commissioning-tasks/-/work_items/8

Paola has kindly explained how the 50Hz feed-forward into DARM is implemented in the DSP and I have replicated the method in Acl. The environmental channel is bandpassed around 50Hz and then a variable delay+gain filter is applied to the environmental channel with two continuously updated parameters. The filter gain is a simple product by a parameter, and the dephasing is formed by implementing an (s-s0)/(s+s0) filter manually in Acl retaining in a separate channel the previous value of a channel.

To obtain error signals for those two parameters the PSTAB channel after after adding the  feed-forward correction  is band passed at 50Hz, and multiplied by the environmental channel band passed around 50Hz and filtered by the dephasing filter. After low passing the result this yields the error signal for the gain parameter of the feedforward. 

To obtain the delay parameter error signal, the environmental channel is first filtered by a pole at 1Hz, to dephase it by 90 degrees before multplying it with the PSTAB channel band passed at 50Hz and low-passing. In this way the other quadrature of the demodulation of the PSTAB by the environmental channel is obtained.

To test the Acl implementation Alain has setup a test process Acl17_INJ in the test instance of VPM: https://vpm.virgo.infn.it:40010/main.html?subsystem=Tests&process=Acl17_INJ

To access the data from it one needs to change the Cmdomain using the command "cmdomain CascinaTest" before starting dataDisplay, and then choosing the FbmMainTestUsers online server.

Figure 1 shows that after fixing many mistakes the 50Hz feed-back works in a test, reducing the 50Hz line in the target PSTAB channel by two orders of magnitude. FF_product_I/Q are the two error signals, while FF_gain and FF_z0 are the two variable parameters of the feed-forward filter. The adjustment of those filters is done using a simple pure integrator of the error signals, and the adjustment loop UGF is around 0.2Hz, I haven't tried to increase the UGF further.

One important aspect was to do the demodulation for calculating the FF_product_I/Q error signals after applying the dephasing signal to the environmental channel, so that the loop automatically tunes the demodulation phase. Initially the loop was not working at all, as the 50Hz line in the PSTAB channel was ~90 degree out of phase with the line in the environmental channel, which was swapping the two error signals.

This could be tested at some point on the actual PSTAB, starting from next week, to see if that idea works in practice. The code naming need to be first cleaned up, added into the ISYSnoise process to include it into the existing PSTAB_NOISE channel, and eventually replicated for all of the lines in the 50Hz harmanics comb.

During the recovery of the Injection system in May, we had to search manually for a new alignment of the IMC cavity, in order to continue with the all the other checks.

However, with the chosen position we had quite large offset on both DC QPD (MC transmission) and RF QPD (Dihedron reflection) in addition to the one on the longitudinal lock. Moreover, we usually apply offset on the erorr signals after the sensing matrix (IB_{TX, TY, TZ}, MC_{TX, TY}), thus generally mixing the offset on DC and RF quadrants.

As first step to improve the working point, we tried to zeroing the RF signals (INJ_IMC_QD_{NF,FF}_I_{H,V}) by manually mixing all the AA offset ( IB_{tx,ty,tz}_set and MC_{tx,ty}_set). In addition, we were also brought back the beam on the MC close to the position of last March (looking at INJ_MCT_{h,v}_err). The results are shown in fig. 1: reducing the offset on the RF quadrants reduced the frequency to amplitude coupling (new IMC_SET offset is now -1.5) and clearly improved the alignment of the RFC. In addition, not completely unexpected, there was a change on the PSTAB photodiodes, that induced a small improvement on the PSTAB correction noise.

We then modified the AA loop on ACL in order to better take into account the offset on the DC quadrant ({NF,FF}_AC{h,v}_SET, MCT_{h,v}_SET) and recomputed the AA matrix accordingly. We closed the AA in full bandwith at the end of the work (fig.2).