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
MHz-bandwidth magnets are widely used in Hadron machines as well as therapy machines for a fast switching (for machine projection) and a fast kicker magnet. This is also necessary to inject or extract beams to/from a ring. But these kickers are using a ferrite core since this can achieve the field requirement.
M.J. Barnes: https://cds.cern.ch/record/1334789/files/141.pdf
Recent progress in material research, particularly on Magnetic Alloy, allows accessing that bandwidth (a few MHz) for the core, which is used for a magnetic-alloy-loaded cavity.
C. Ohmori: https://journals.aps.org/prab/abstract/10.1103/PhysRevSTAB.16.112002
Thanks a lot for your answer, the links are very interesting.
In fact my question was more about the use of such a magnet not as a kicker to inject or extract beam, but more as a correction magnet or for machine physics studies. We also have kicker magnets for the injection scheme, and in fact the design is very similar to our shaker. For the kickers we also use a core made of the material called 8C11, and to be honest I don't know how it compares to the Magnetic alloy you mention.