Virgo Logbook

Injection system (Laser power stabilization)

lagabbe, gosselin, melo - 19:07 Wednesday 04 March 2026 (68817)

Alignement of the PMC cavity

Probably due to the blackout of March 1, the laser beam on laser bench was slighly misaligned with the PMC cavity, which worsens the laser power stabilization loop and add some noise on the laser power noise.

On wednesday March 4 around 15:10 UTC, we re-aligned the incoming beam of the cavity by adjusting the orientation of one of the mirrors before, LB_M12.

The 2 figures show the time series and the spectral desities of the power stabilisation photodiodes. After realigning the PMC cavity, its output power increased a bit, as seen in the time plot. And the laser power noise was reduced, especially at low frequency below 2Hz, as shown in the FFT plot.

As seen in the FFT plot with the signal taken before the blackout. The current noise level is slighly higher then before the blackout, and some "sidebands" at 1 Hz around the 50 Hz signal appeared. This may be caused by the eletric system, but we don't know yet their origin.

Images attached to this report

68817_1772646481_2026-03-04_PMC_before_blackout_FFT.png

Comments to this report:

lagabbe, gosselin, melo - 19:13 Wednesday 04 March 2026 (68820)

The 1Hz "sidebands" observed in the laser power signal comes from the power subbly of the central building. Especially in the ENV_CEB_UPS_CURR_R channel. These sidebands were not present before the blackout.

Images attached to this comment

68820_1772647652_2026-03-04_CEB_UPS_after_blackout_FFT.png

68820_1772647727_2026-03-04_CEB_UPS_before_blackout_FFT.png

Paoletti - 23:27 Wednesday 04 March 2026 (68822)

The IB tower magnetometers show the strongest 1 Hz comb magnetic component, indicating a possible source in the nearby area (LL or INJ_EE_room) powered from a single UPS phase (R phase).
The same 1 Hz comb is visible in the CEB magnetometers and in the External Magnetometer, even though the latter is located at a significant distance from the CEB.

It is also worth noting that the UPS is located very close to the IB tower, a configuration that may account for the higher magnetic level measured by the tower magnetometer.

Images attached to this comment

Paoletti - 9:14 Thursday 05 March 2026 (68824)

Curiously, the same 1 Hz comb appears in the current of all three IPS phases, with an amplitude similar to the peaks seen in the UPS line’s R phase.

Nothing relevant is present in the MCB monitors.

Images attached to this comment

Tringali - 10:14 Thursday 05 March 2026 (68825)

A similar feature was observed in the past from the cooling system of the CO2 main lasers, which produced a 1 Hz comb visible in the UPS current and voltage monitors. This comb disappeared when the chillers operated in “power-save” mode. The signal observed here could therefore be related to a similar mechanism.

It would be useful to verify how the devices were powered back on and check which operating mode they are currently in.

Past investigations:

https://logbook.virgo-gw.eu/virgo/?r=63358

https://logbook.virgo-gw.eu/virgo/?r=63357

https://logbook.virgo-gw.eu/virgo/?r=40113

spinicelli - 12:36 Thursday 05 March 2026 (68828)

Indeed, that effect was visible in the past also on the INJ/PSL signals (fig.1) but with a much smaller effect compared to what is seen now(fig. 2).

This may be due to the fact that, starting from 22nd of October 2024, we are using one of the chiller borrowed by TCS team for the Neovan electronics (located in EEROOM). Thus, a check of the settings of this chiller is planned for today.

Images attached to this comment