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Detector Characterisation (Spectral lines)

mwas - 11:53 Tuesday 10 December 2024 (65760)

~120Hz bump is related to SWEB / B8 DC

Figure 1. Bruco finds a low level coherence between SWEB B8 DC and Hrec at ~120Hz

Figure 2 and 3 show that noise at ~120Hz increases both on B8 and in Hrec at similar times over a week long period, but the time correlation is not very clear.

Next steps should be to check if there are recent environmental noise injections in the WE building which could find a coherence around 120Hz, and to perform noise injections into SWEB local controls around 120Hz to check if a resonance at 120Hz could be excited.

It may actually be an old problem. At the end of O3 there was a bump at ~125Hz that appeared and was related to SWEB signals: https://logbook.virgo-gw.eu/virgo/?r=48854

Based on O3 data it might have a smaller sidebump at 110Hz https://logbook.virgo-gw.eu/virgo/?r=48745

Images attached to this report

65760_1733816360_Screenshot from 2024-12-10 07-27-44.png

65760_1733816443_Screenshot from 2024-12-10 07-37-49.png

65760_1733816451_Screenshot from 2024-12-10 07-37-55.png

Comments to this report:

mwas - 20:40 Friday 13 December 2024 (65803)

There was a test done to study the 120Hz on B8 DC / Hrec yesterday by adding an alignment offset into the soft (minus) mode of the west arm alignment in the vertical direction.

Figure 1 shows the trend of data during that test with WE MIR Y AA the offset in the vertical position of the beam on the mirror. There is an unlock in the middle of that time series.

Figure 2. shows the spectrogram of DARM for that day, and between 18h00 and 18h30 the bump at 120Hz disappears when there is a negative offset on WE Y.

Figure 3 looking at spectra of h(t) the change in the bump is less clearly visible

Figure 4 looking in the B8 DC spectrum both in LN3 and in CARM NULL 1F there are clearly changes in the height of the 120Hz bump. The relation is not very clear with WE Y, but the bump tends to be smaller for negative offsets on WE Y.

To understand better this relation the position on the WE mirror would need to be scanned in CARM NULL 1F over a wider range and also in the horizontal direction.

Images attached to this comment