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
It is a bit different issue but I have observed the 50 Hz ground motion in our optical table with a vibration sensor. We found that the source was small chillers installed onto a vibration damped carriage. The 50 Hz noise disappeared (please see the attached figure) when the chillers are off for the summer shutdown. It may possible to check the motion with a vibration sensor. Then, it would be clear that the motion is real or artefact.
At ESRF we have been exploring the possibility to do single-electron control and measurement with the use of 4 screens in TL2 and a simple and low-cost Photon Multiplier Tube (PMT) installed in the visible-light laboratory (ID04). We could inject 1-2-3-4-5 electrons the EBS ring. The first direct application was the measure of the beam purity during MDTs. We are going to install a Pico-Harp and a Time-Correlated-Photon-Counter (TCPC), for a bunch-purity measurement that may allow to cover up to 10e-11 dynamic range during User-mode operation (USM). Find attached the first measurements. If you have any question or suggestion, please comment.
It is indeed quite puzzling. Also it seems that it is not a pure 50 Hz sine wave perturbation, but rather a square signal with varying duty cycle. This suggests that it is not just a coupling with mains power supply.
Can you try to capture the signal seen by each channels (Va, Vb, Vc, Vd) to see if it is present on all of them, or just two? Does the sum signal also have this behavior?
Last post by Laura - November 24, 2021, 01:24:31 PM
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