My idea was to use our collective knowledge to help the CERN people to "hunt the hump".
So, if you have an idea on what the hump could be, on how the cause of the hump could be found, please join in!
We start with what we already know about the hump:
- The hump is so called because it causes a hump space on the tune graph, which is a FFT transform of the beam oscillations;
mainly on the vertical one.
In plain English, this means something is jiggling the beam up and down.
- If we know the cause of the hump, it is probably not hard to reduce the hump (e.g. by shielding something).
- The hump decreases the quality of the beams (increasing lifetimes), so we really want to get rid of it.
- Collimator settings are complicated by the hump, but they do not cause the hump.
- It must be something that has a magnetic field to move protons (a motor, for example).
- It is a "noisy" sound, not a clear tone (otherwise it would be a peak, not a hump).
- Its frequency varies from 2.6kHz to 3.7kHz (that is .23 to .33 times the rotation frequency of the beam of 11.2 kHz).
- The frequency moves up and down over this range every 7-10 minutes (depending on something).
- It is still there if SPS is off.
- In theory, the frequency could be an integral multiple of 11.2 kHz higher (but they think that's unlikely).
- Shape of the hump (look at the bottom graph around .25): https://ab-dep-op-elogbook.web.cern.ch/ ... Id=1068503
- Several measurements, concluding that SPS is not the cause and that it moves up and down in 10 minutes; scroll down to 12:02: https://ab-dep-op-elogbook.web.cern.ch/ ... Id=1025745
- Hump disrupting collimator setting process: https://ab-dep-op-elogbook.web.cern.ch/ ... Id=1025709
- Here they programmed the tune device to follow the hump (look at 12:40), and compared it to a water pump: https://ab-dep-op-elogbook.web.cern.ch/ ... Id=1025669
Note that the hump moves here every 7 minutes, instead of 10.
If somebody has an idea, please post! Maybe together we can help them with finding this nasty problem.