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Good idea, I will try next week (shutdown)!

Well, the step I observe with BPMs is 4 um so I should be able to see it with accelerometers!
Also, sometime it is a jump: it does not go back to the previous location...
I will keep you updated!

Hello Ji-Gwang,
Indeed we also suspect some cooling system but we have not been able to identify it. We put some accelerometers in the tunnel on the block and on the girder and in both case we see this strange frequency but we could not identify the source, moreover the frequency is there either we observe or we do not observe vibrations in the BPM data. As you suggest we can try to do some tests with accelerometers during shutdown switching off each of the element to see if the movement measured with acceleromters stop in some case.
Thanks!
Laura

The second graph is what we see when both BPM and corrector were out of the FOFB loop: we could still see the noise and, since they were not in the loop, the jumps were not corrected (i guess). If you zoom at the jump you would see the same 50 Hz pattern (as in the third plot, unfortunately I don't have a zoom of this specific graph).
The first plot is how the noise appear usually when the BPM and the corrector are in the loop.
I think this is a noise that somehow enter in the BPM and then the FOFB try to correct and propagate it through the sector.
The last plot is an FFT of the noise. The 50Hz line appears broader.
What I don't understand is that it appears only in vertical... If it was some random noise leaking in the buttons/cables it would be in both planes.
I am quite lost 

Hello,
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,

Laura

Hello,
At ALBA we have in total 120 BPMs (Libera Brilliance) in the storage ring and we use 88 for feedback to have squared matrix, since we have 88 correctors (WEPD23 https://www.slac.stanford.edu/econf/C140914/papers/wepd23.pdf).
They are doing quite well after ~ 10 years operation but this year fans started to fail consistently and we decided to perform a full replacement campaign.
We are also testing 2 Libera Brimmiance+ and Libera Spark+Pilot-tone in some special BPMs.
In the Booster, we have 44 BPMs, 24 of them are equipped with a Libera Brilliance but we really only use 8. One BPM (the first after injection) is equipped with a Libera Spark Single pass and we use it for Linac to Booster injection efficiency measurements.
In the Linac and in the transfer lines we iindeed use Libra Spark Single Pass (Upgrade of BPMs and SRMs for the ALBA Booster to Storage Ring transfer line, DEELS 2017 https://www.synchrotron-soleil.fr/fr/evenements/deels-diagnostics-experts-european-light-sources).