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Need help? / Strange vertical 50Hz noise in one BPM
November 24, 2021, 11:30:26 AM
I am struggling with this since July: we have one BPMs that sees some strange noise only in the vertical direction. The frequency of this noise is 50 Hz.
The problem is that this BPM is in the FOFB loop and the noise is then spread around the whole sector.

We have:
- Checked and changed the associated corrector (but the noise frequency was already telling us that it was not the guilty one)
- Changed the Libera (even if the noise was only in vertical)
These modification provided no results.

Moreover this noise is not always present. We are sure that it is seen by this particular BPM since we removed corrector and BPM from the FOFB loop and we could see the noise in the vertical BPMs data even when it was out from the feedback. The other BPMs of the sector did not show anything.

I can add that this BPM is located in the middle of a standard sector (no IDs or cavities close by).
I also want to stress that this noise is observed only in the vertical direction.

Has it happens to some of you? Do you have some suggestion.

Thanks in advance,