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Detector Characterisation (Broadband noise)
mwas - 6:11 Wednesday 05 June 2024 (64426) Print this report
Bump around 48Hz since last maintenance

Figure 1 since the last maintenance the BNS range has been at ~45Mpc instead of ~55Mpc

Figure 2 There is a line at ~48Hz that is 10 times higher than before the maintenance, and a broad bump +/-20Hz around it. This is probably related to the cross-bar of one of the suspensions.

There is the WI DSP that had a timing issues starting during the maintenance . Then intervention of Valerio has removed the timing issue as seen by the DAQ, but after it the calibration processes started complaining there is a timing issues with the WI. It needs to be understood if this is related to the excess nose around 48Hz and how.


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mwas - 9:15 Wednesday 05 June 2024 (64429) Print this report

Another thing that happened during the maintenance is that the north end building has been cleaned: . Could have something been damaged, or a cable disconnected during the cleaning that causes the 48Hz bump to be high?

direnzo - 9:22 Wednesday 05 June 2024 (64431) Print this report

Unfortunately, a dedicated BruCo run with all the channels highlighted no significant coherence for Hrec at the frequency of the line and bump: link to results. Also for the cross-bar resonance mode itself, we usually don't see any coherence during usual operation conditions.

rolland - 9:25 Wednesday 05 June 2024 (64430) Print this report

About the red calibration flags on WI, since yesterday slightly after 16h UTC: they indicate that there is 50 µs munsynchronisation of the WI DSP (see the jump in the bottom left plots of figures 1 and 2, and figure 4). This is the case since when Valerio synchronized the WI DSP to fix the red timing flag (see figure 3).

--> for calibration point of view, the WI DSP must be resynchronized before the next Calibration data taking (tonight).

--> WI  is also actuated for the 50 Hz damping loop, but it is not clear if this issue of synchronisation  could generate such a bump around ~48 Hz.


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fiori - 9:40 Wednesday 05 June 2024 (64432) Print this report

The excited peak pair, 48.08 and 70.02 Hz, best match the crossbar modes of the WE, as measured with magnetic injections.

Here the table from VIR-0300A-24:

tower 1st mode 2nd mode
NI 47.65 70.8
NE 47.75 70.6
WI 48.75 71.4
WE 48.1 70.3

I remind the direct measurement done by Paolo in O3. They roughly match the above, except that NE (47.75 Hz here, around 48.4 Hz in O3).

Paoletti, Tringali, Fiori - 14:13 Thursday 06 June 2024 (64447) Print this report

We found the source of the 48Hz bump.
It comes from a WE motor crate, the one that drives the MH.MA.1 and MH.MA.2 motors. We don't know why this new coupling mechanism has occured since Tuesday, but removing the mains cable from an unpowered crate was sufficient to eliminate the noise.

We leave the power cord reconnected but the front panel switch in the OFF position (it is equivalent).

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direnzo - 10:25 Friday 07 June 2024 (64454) Print this report

I'm just adding a few pointers to help understand why this issue occurred. In fact, the same exact problem already happened on October 11 2023. These are the relevant logbook entries: #62060, #61792, #61959

Paoletti, Tringali, Fiori - 10:31 Friday 07 June 2024 (64453) Print this report

During yesterday's investigation, we injected a far-field magnetic sweep with the aim of cross-checking and identifying each resonance frequency of the crossbars.

Here is what came out:

NEB 48.16 Hz 70.55 Hz    
WEB 48.09 Hz 48.38 Hz 70.24 Hz  
CEB 47.52 Hz 47.74 Hz 48.34 Hz 48.63 Hz

It is interesting to see that after the “disconnection” of the WEB motor crate (and disappearance of the noise) there remains something in Hrec that seems to be associated with CEB (47.52 Hz and 47.74 Hz) and WEB (48.09 Hz). This is an indication that we might gain something more in terms of Mpc if we could find and reduce some other sources.

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