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General Discussion / Do you have fast magnet (bandw...
Last post by Benoît Roche - May 10, 2022, 03:15:59 PM
At the ESRF we use what we call "magnetic shakers". It is more or less a special magnet with a high bandwidth (a few MHz). To have such a high bandwidth we need a ceramic vacuum chamber with titanium coating in order to reduce the eddy currents. This is the same kind of vacuum chamber used for the injection kickers. The magnet itself is a coil with just a few loops.

My question to everyone is: do you have a similar device in your ring? If yes, what do you do with it? And how do you call it?

Of course you may have strip-line kickers (for a bunch-by-bunch feedback), which have a much higher bandwidth (of the order of 1 GHz). So you may ask what is the purpose of a fast magnet with a lower bandwidth. The main advantage of this fast magnet (or shaker as we call it) is that it is roughly 10 time more powerful than a strip-line kicker for the same amplifier power in the DC -> few MHz regime.

We use this device mostly for 3 purposes:

  • Transverse betatron excitation for tune measurement and beam emittance blow-up (high amplitudes are required for beam dynamics studies),
  • Compensate the perturbations induced by the injection kickers during refills,
  • Protect the machine when a interlock occurs: before killing the beam, we increase the vertical beam profile as much as possible by resonant betatron excitation to protect the vacuum chamber and collimators from the energy deposition due to electrons hitting these elements.

I would be happy to know if similar devices exists in other institutes. Thanks
Need help? / Re: Strange vertical 50Hz nois...
Last post by Laura - May 09, 2022, 11:26:09 AM
Good idea, I will try next week (shutdown)!
Need help? / Re: Strange vertical 50Hz nois...
Last post by Benoît Roche - May 09, 2022, 11:05:19 AM
Just an idea: maybe it could be an "impurity" which is in the vaccum chamber between the button and the vaccum chamber a create a non-infinite resistance. Sometimes the impurity creates the short-circut, sometime it does not.

It does not explain everything (why the perturbation is only in the vertical plane? why 50 Hz?), but it is easy to check with only a multimeter (without beam).
Need help? / Re: Strange vertical 50Hz nois...
Last post by Laura - May 05, 2022, 11:34:25 AM
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!
Need help? / Re: Strange vertical 50Hz nois...
Last post by Ji-Gwang Hwang - May 05, 2022, 08:35:44 AM
 Hello Laura,

It is good to hear that you did the test with accelerometers. In general, the sensitivity of the accelerometers (depending on the model and frequency) is an order of magnitude better (less than 100 nm) than the BPMs (~ 1 um). This could explain the discrepancy between the two monitors.

If the vibration amplitude is changing daily (especially more in summer), the cooling system would be the source since the water flow/pressure is variating to fight against the temperature raising in the tunnel or circumstance. But I am not sure whether the cooling water could drive the 50 Hz noise. In my case, the compressor of the chiller was working with that frequency which is equivalent to the frequency of the main powerline in Germany.

Best regards

Ji-Gwang Hwang
Need help? / Re: Strange vertical 50Hz nois...
Last post by Laura - May 04, 2022, 09:04:04 AM
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.
Announcements / Open for doctoral student posi...
Last post by Ji-Gwang Hwang - May 03, 2022, 02:38:30 PM
We have recently opened a doctoral student position to work on beam diagnostics/dynamics:


Feel free to ask any questions.

Ji-Gwang Hwang
Need help? / Re: Strange vertical 50Hz nois...
Last post by Ji-Gwang Hwang - May 03, 2022, 02:33:16 PM
 Dear 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.

Best regards

Ji-Gwang Hwang
General Discussion / Re: SINGLE ELECTRON MEASUREMEN...
Last post by Ji-Gwang Hwang - May 03, 2022, 01:42:04 PM
Similar work has been done in Metrology Light Source for a primary radiation source standard but with a different approach (scraping from high-current to a single electron and cooled photodiode).

See Figure 12 c of Publication in PRST-AB:

It looks like the previous measurement from MLS has a better signal-to-noise ratio.
What would be the advantage to use the high-efficiency PMT?
Announcements / Open post doctoral positions a...
Last post by nicolas.hubert - April 19, 2022, 05:21:24 PM
We have recently opened at SOLEIL 2 postdoctoral positions to work on the design of some SOLEIL-Upgrade diagnostics:

•   Photon BPM:

•   Optical diagnostics for the new booster:

Don't hesitate to apply!

Nicolas HUBERT
Head of Diagnostics and Timing Group
Synchrotron SOLEIL – Accelerators & Engineering Division
L'Orme des Merisiers BP 48
91192 Saint AUBIN - FRANCE