Last post by cozkan - August 11, 2022, 06:54:15 PM
Hello, Does anyone have any experience simulating the effect of the thermal heatload on the surface of a monochromator crystal? We would like to couple this with focusing xray optics to simulate its impact. This could be with SHADOW, for example. Thank you.
At ESRF we used to have (in the previous machine) a longitudinal feedback with a QPSK modulator as backend. It was an home-made system, and I'll be honest it was a bit complicated and it was not very easy to adjust the different delays etc..
A few months before the end of the previous machine we tried to simplify a lot the backend. We wanted to have something very easy to maintain and install in case we need it for our new machine. If I remember well we just used a mixer with a LO at 4 times the master source frequency, and a bandpass filter from Mini-Circuit. We did only a few tests and it seems that working well. The comparison with the QPSK modulator was quite satisfying.
Then we installed our new machine and it was decided to not have a longitudinal feedback anymore. Today it is not required at all.
So it seems to me that a very simple, home-made backend can be used. However I don't have a lot of experience with it, so maybe there are some performance issue that I am not aware of.
Last post by Nashat1985 - July 02, 2022, 02:32:20 PM
Dear Experts, This Nashat Sawai from SESAME synchrotron, it is first time posting here Currently, we are working on the design and implementing longitudinal feedback for our storage ring, we run a 500 MHZ RF system.
we already have some components for feedback and still missing the other components such as the Backend and cavity kicker, we intend to use the i-Tech Libera bunch-by-bunch processer, does anybody have used Libera electronics for longitudinal feedback ?! what is the typical setup for modulator/backend? should we use DSB or do I need QPSK modulator? Your comments and feedback are greatly appreciated regards Nashat
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.
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
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
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).
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.