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AdV-COM (AdV commissioning (1st part) )

fiori - 16:06 Wednesday 25 October 2017 (39867)

peaks

The following plots compare Hrec structures at four times: one time with good sensitivity sept 23 (30Mpc), two times with worsened sensitivity before the venting (sept 30 and Oct 8) and then last night (Oct 24 at 22:30).

Figure 1: 50-100Hz, Figure 2: 100-170Hz, Figure 3 (170-240) Figure 4 (240-290) Figure 5 (290-600) Figure 6 (zoom-in 400-450).

A few peaks disappeared with respect to before venting:

peaks at 255Hz and around 260Hz and something around 280Hz disappeared (these peaks were coupling acoustically in CEB and at least some of them were found to be due cooling fans) - see it in Figure 4.

A few peaks disappeared or moved with respect to before venting:

410Hz and 440Hz disappeared, but new ones appeared at 401Hz, 420Hz, and around 450Hz. - see Figure 6

A few peaks appeared or enhanced with respect to before the venting:

new peaks around 55Hz (Figure 1)
new (and ehanced) peaks around 200Hz (Figure 3)
several enhanced peaks but also new peaks between 300 and 600Hz (Figure 5).

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Comments to this report:

fiori - 16:23 Wednesday 25 October 2017 (39868)

Bruco coherence tables of last night (here the link to the full set of channels, and to the restricted ENV set) indicate that at several peaks between 200 and 600Hz there is large coherence with PRCL and input angular noise signals (not much with SSFS).

Figure 1 compares the coherence last night and on Oct. 8th. The coherence increased on the same peaks but the sensing did not, which might indicate an increase of coupling of common mode noise to ITF (?)

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mwas - 11:23 Thursday 26 October 2017 (39881)

The coupling of common noise (laser frequency) has indeed increased by a factor ~2.5.

This can be seen also in the noise budget: figure 2 before the interventions, figure 1 after the interventions.
The noise budget looks at the 1111Hz line amplitude seen in DARM to scale the noise projection. And the SSFS noise projections clearly goes up by a factor 2.5.
The SSFS sensing quantum noise also goes up, compare figure 3 and 4. This explains the broad band ~0.4 coherence between DARM and PRCL from 200Hz to a few kHz (figure 5).

Figure 6, using yesterday's BPC noise injections. The peaks above 100Hz that are coherent with PRCL, are well explained by a direct BPC coupling, and not going through the PRCL path.
On the contrary, for the ~47Hz line and ~56Hz lines, the noise is well explained by lines being present on the PRCL error signal and being fed back to the PR mirror.

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