Virgo Logbook

AdV-ISC (Alignment control scheme conceptual design)

casanueva, mantovani - 16:30 Thursday 31 May 2018 (41625)

CMRF evolution

We have taken a look to the ratio between the amplitude of the 3345 Hz line at the SSFS and at Hrec. Figure 1 shows a comparison of this ratio in the last 25 days and during O2. We can see a trend of increase of a factor almost 4 so far. Figure 2 shows a 2D plot of the range against the ratio between the lines. HOwever, the correlation between both is not clear.

It is very difficult to correlate this trend with a particular parameter, so we will continue with the investigations.

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Comments to this report:

mwas - 14:04 Friday 01 June 2018 (41645)

Looking at the height of the 1111Hz and 3345Hz lines on short time scales, they are clearly moving up and down in DARM together as they should given they are both frequency noise lines. See #41547 for an earlier example.
See figure 1 and 2 for examples, clearly the 1111Hz line has much better SNR.

Figure 3, looking at the spectrum of the height line at different times. It is often without clear features. But for a time two nights ago and last year during O2 (red and gold lines), there were clear lines at 0.42Hz and 0.85Hz and a bump at 1.52Hz.
I wonder if that points towards an angular degree of freedom. Also after the large improvement in alignment control yesterday (blue line), the fluctuations below 0.1Hz decreased by a factor few (blue is better than black or red). This could mean that the alignment control is better, but that there is some hidden offset (at least from the CMRF point of view).

Looking at the correlation between the line height and angular signals, there is some relation with the IMC alignment.
Figure 4, shows the spectrum of the line height, with a bump at 0.7Hz, figure 5 this bump is present in the IMC quadrant signals, and it is even coherent figure 6.

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mwas, masserot - 17:05 Friday 01 June 2018 (41656)

To ease investigation of correlation between frequency noise coupling and alignment (or other) signals, we have added the demodulated magnitude of the 1111Hz and 3345Hz lines seen in LSC_DARM and LSC_PRCL to the frame.

In particular LSC_DARM_FMOD_LINE_mag_100Hz is a good channel to look at and could be used for alignment tuning by minimizing it.

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