Activities communicated to the control room:

• Confined space safety training

• NI CP mount assembly (Travasso)

• TCS Chiller assembly & test (Zaza)

I confirm that NI tower is still safe wrt laser hazard

This morning from 10:30h to 11h LT we went to the laser lab to realign the beam onto the PMC. We slightly improved the power transmitted by the PMC (Fig. 1) looking at the reflection of the cavity and trying to minimize the 01 mode on the oscilloscope. Afterwards, we flipped down the mirror at the end of the Laser Bench to allow to beam to reach the BPL loop so we can work on it in the next days.

Since May 17 the gravimeter was not reachable from remote. This has been fixed today. Attached are two pictures of the gravimeter (Fig.1) and the laser box (Fig.2).

The issue was with the USB-to-RJ45 adapter, which for some reason was not working properly (the network communication LEDs were off, and the network interface was also disconnected from the console). After unplugging and reconnecting it, the connection was restored, but it went down again a few minutes later. The procedure was repeated, and the connection was re-established. Now, after returning, the machine appears to still be up and running.

Measurement continued through the Cascina holiday, and approximately 48 hours of data was stored.

I evaluated the ASD peak heights for the 1 Hz comb and 50 Hz power line hourly, and plotted their median, max, and min values.

To eliminate calibration uncertainty, the values are expressed in counts.

The median value of the 1 Hz peak was highly stable, whereas other metrics showed temporal variation.

Graphs show data of the accelerometer installed (vertical) on the floor next to the Gravimeter. Fig.1 shows that the noise conditions is more or less stable over 24 hours. Figure 2 compares the spectral noise with one accelerometer sensor (vertical) on the CEB floor (near Guralp). The Fiber lab floor is noisier above 10Hz and below 1Hz.  

related logbook: https://logbook.virgo-gw.eu/virgo/?r=69040

We measured magnetic field at WT 900m, where less instrumental noise is expected. 
We used a portable setup with Bartington Mag-03 MC100 + Nanometrics Centaur.
These data; time series, ASDs, and spectrogram are plotted here. We can see the 1, 2, 3, ... Hz comb noise stationally. 

(NOTE: Calibration should be confirmed)

The slave laser remained stable over the weekend, so this morning we continued working on the alignment.
We seeded the Neovan with the SL and everything was as we let it on Friday afternoon.

We first attempted to optimize the alignment using the mirror in front of the Neovan while monitoring both the transmitted power and the beam profile on AMP_cam.

Since the improvement remained limited and the AMP NF was still significantly away from what it was before, we decided to realign the SL beam towards the Neovan using LB_M04 (the second mirror after the SL) hoping for both effect on the shift and the tilt of the beam inside the neovan. This proved to be very beneficial for both the output power and the beam profile. We managed to recover 0.38 V on AMP_DC.

We then adjusted the Neovan pumping diodes to investigate whether the situation could be further improved. We decreased the current of all four pumping diodes by 0.1 A and obtained a better output beam shape together with a lower temperature of the Neovan head, while maintaining good output power (Figure 1).
New pumping diode current values: 4.8 A.

Overall, we now measure 0.37 V on AMP_DC, compared to 0.34 V previously, and the low-frequency noise is reduced (Figure 2).

The beam shape also looks improved (Figures 3 before and figure 4 after).

Having recovered both good output power and a good beam shape, we proceeded to work on the PMC alignment.
We realigned it and now measure 0.52 V at the output, compared to 0.49 V previously (Figure 5).

While normalizing PMC_TRA and PMC_REFL with AMP_DC, the throughput initially appeared lower. However, after further inspection, it seems that about 3.7% is still coupled into the TEM01 mode. This should recover once the system is fully thermalized. The mismatch is instead around 1%.

We also computed the throughput using PMC_REFL in the unlocked and locked states. We now estimate throughput losses of 20%, whereas they used to be around 22%.

It should be noted that, since the IMC transmission signal is currently unavailable, we could neither work on the PSTAB nor easily verify the alignment in the AOM. These checks will need to be performed later. However, only minor adjustments were required for the alignment towards the PMC.

We let everything locked for the coming days for thermalization. Fine alignment of the PMC as well as check of the order 1 in the AOM will be done on wednesday. 

YAG beam is blocked into LaserLab, with IMC unlocked and SIB1 valve closed. There is  no main laser beam in the interferometer.

CO2 lasers are switched off as well as the green ones. 

Confirm that there is no laser hazard to enter the NI tower.

fter discussing it with Walid in the morning, we decided to intervene on the SL fiber alignment to see whether we could recover power at the slave output and improve the cavity alignment toward the Neovan.

We started by switching off the SL and taking additional references of the beam going from the ML toward the neovan (in reflection of the SL), since we had previously observed that the Neovan output power was quite good when it was seeded only by the ML.

We then worked on the alignment inside the SL cavity by acting on the vertical and horizontal axes of both fibers, recovering the alignment with the lenses, trying to maximize the output power. We managed to recover about 0.34 V, starting from 0.32 V. We could not go higher and get back to the 0.38V because both axes of the lens on the western side had reached the end of their coarse adjustment range.

From there, having only 10% missing, we started to check the alignment toward the Neovan, and it was better than what we had yesterday. We had to slightly adjust the tilt by acting M0.4 (second mirror at SL output).
We injected the SL into the Neovan and slowly increased its power using the IPC between the two.

We eventually recovered 0.35 V on AMP_DC, which is better than what we had before. From the AMP diagbox QPD signals, the beam appears to be mainly shifted horizontally compared to its previous position (figure). In addition, the temperature of the Neovan head is slightly higher, around 31°C instead of 30°C.

We did not try to realign the PMC for now, but looking at the peaks on PMC_TRA, it appeared to be misaligned, as expected given the signals on the AMP QPD.

For the weekend, we decided to flip the mirror between the SL and the Neovan and reduce the current of the Neovan pumping diodes to avoid the head to overheat. We will monitor the thermal behavior of the SL over the weekend.

The next steps are to reinject again the SL into the Neovan, check whether a slight alignment of the beam inside the Neovan could further increase the output power, and realign the PMC in order to eventually try locking it.

ITF found DOWN in UPGRADING mode.
- Slave laser pumping realignment (Melo, Gosselin)
- NO other activities communicated to the control room.

Some results:

• Figure 1 shows and overview of microphones and accelerometers on the LB and EIB benches during the test period. A significant reduction of vibration noise on the LB occurs in correspondence of the switch off of the NEOVAN head chiller at 13:09. There is also a correspondent reduction of acoustic noise on LB. No effect is seen on the nearby EIB.
• Figure 2 is the same but up to 10kHz, showing that both the NEOVAN chiller and the HVAC also contribute noise up to some kHz. At 14:50 about the Neovan chiller has been turned back on (as confirmed by the INJ team).
• Figure 3 zooms on the region around 50Hz which shows a noise associated to the Neovan electronics chiller (on-off sequence 13:39-13:52)
• Figure 4 zooms on a drifting vibro-acoustic noise line starting at approx  500Hz, which never disappeared during the test. Its frequency drift visually correlates, with some delay, with the temperature inside the Lab and the EIB (Figure 5).
• Figure 6 is the same set of spectrograms in the low frequency (below 5Hz): acoustic spectra are "polluted" by some burst noise which might also be associated to people who was working on the platform at that time (nobody was entering the Lab instead) 
• Follows a set of spectra comparing the noise associated to single devices which were swithed off:
  • HVAC noise - Figure 7 (the off time corrsponds to also the CEB HVAC off): we remind that during this test the Towers HVAC in CEB was on and its noise was sensed inside the laser lab.
  • Neovan head chiller (Termotec) - Figure 8: the noise contribution is evident between 100 Hz and  1kHz. It could be the noise noticed in https://logbook.virgo-gw.eu/virgo/?r=68639.
  • Neovan electronics chiller - Figure 9: it contributes with a line at about 47 Hz (also in Figure 3). This noise is sensed louder by NN geophones on the EEroom floor (look at the red colored spectra which are in units of acceleration - m/s2). 
  • Main chiller (OMI) - Figure 10 - no noise evidence from this chiller.

20/05

Yesterday, while relocking the SL, we noticed that the reflection was quite low: 0.22 V instead of the usual 0.38 V.
When the NeoVan was seeded only by the ML, we obtained higher power than when it was seeded with both the ML and SL.
The SL PUMP DC signals, which monitor the pumping diode power at the output of the fiber in the SL head, were also higher.

This indicates a general misalignment of the SL cavity that needed to be cured. 

Since the temperature of the NeoVan was increasing, we decided to slightly reduce the pumping diode current overnight while keeping the SL running, hoping that thermalization during the night would improve the situation.

21/05

No thermalization effect was observed overnight.

In the morning we held a meeting with Walid and Margherita to analyze the situation. We agreed that the beam of the pumping diodes needed to be realigned inside the crystals. Since the power was already quite high, we were expeting a slight misalignment that could be recovered by ajusting the lenses in front of the cavity (at least as a first try).
We then went to the laser lab in the afternoon to perform the adjustment. By tuning the vertical and horizontal position of the lenses, we managed to recover the reflection signal up to 0.32 V.
We did not fully recover the nominal value, which was quite expected since we only had a limited number of degrees of freedom available compared to the full possible misalignment that may have occurred.

We also measured the slave locking bandwidth (14:51:02) and found 1.15 MHz, significantly lower than the 2.1 MHz measured last time we did it. This further confirms the presence of a misalignment of the cavity. 
Also, visually, we observed that the beam was not propagating correctly through the optics toward the NeoVan, so we decided to flip the mirror located between the SL and the amplifier. 

Peltier situation:

When the safety interlock triggered on 08/05, the PID temperature controllers did not stop sending correction signals. This was verified this morning by manually triggering the safety system.

Our hypothesis is that, during the afternoon of the 08/05, without cooling from the chiller on the hot side and while the system was still attempting to cool the crystal, the Peltier element of Crystal 1 was receiving 2A and experienced an overall temperature increase. This eventually resulted in a general temperature rise of both peltier, both crystals and likely the whole cavity. 

Activities communicated to the control room:

WE vacuum control unit and CEB cryotraps maintenance (Erbanni, Francescon, Macchia, Pasqualetti)
SL electronics checks (De Rossi, Gosselin, Lagabbe, Spinicelli)
Finalization of the changes to the main building's air conditioning system (Infrastructure Group)