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Messages - Benoît Roche

Hello Nashat,

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.

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.
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).
Need help? / Re: Strange vertical 50Hz noise in one BPM
November 24, 2021, 01:47:49 PM
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?
Need help? / Re: Strange vertical 50Hz noise in one BPM
November 24, 2021, 12:17:09 PM
Hello Laura, I hope you are doing well.

I don't remember having a 50 Hz noise perturbation that was not a real perturbation on the beam, here.

Nevertheless, can you describe a little more your graphs? In particular we can see jumps on the second graph, it is not clear to me if those are related to the noise you have.
Thank you Laura for the details of ALBA BPM system, it is now added to the beginning of this topic.

Thanks Lorraine, I added your contribution to the list.

I see that you plan to upgrade the performances of your Fast Orbit Feedback quite a bit! Increasing the correction bandwidth by a factor 7 is not negligible.

It's a good time to join your team to work on this new and exciting project  ;)
General Discussion / BPM system in different institutes
September 08, 2021, 01:24:17 PM
The idea of this topic is to make the most exhaustive list of the BPMs system in all institutes.

Please indicate what your BPM system is as a reply in this topic, and I will include it in the list.

Later, we could do the same kind of list for other systems (emittance monitors, bunch-by-bunch feedback, XBPM, ...), but for the moment let's start with the most wildly used system in storage rings.

BPM system:120 BPMs (Libera Brilliance) in the storage ring
44 BPMs in the booster, 24 of them are equipped with a Libera Brilliance.
A few Libra Spark Single Pass for the Linac and transfer lines
Upgrade of BPMs and SRMs for the ALBA Booster to Storage Ring transfer line, DEELS 2017
Commissioning of the ALBA Fast Orbit Feedback system, IBIC2014, WEPD23
88 Libera Brilliance among the 120 used for fast orbit feedback to have squared matrix, since we have 88 correctors.
Libera Brilliance are doing quite well after ~ 10 years operation but this year (2021) fans started to fail consistently and we decided to perform a full replacement campaign.
Testing 2 Libera Brilliance+ and Libera Spark+Pilot-tone in some special BPMs.
One BPM (the first after injection) is equipped with a Libera Spark Single pass and we use it for Linac to Booster injection efficiency measurements.
Diamond Light Source
BPM system:172 BPMs on storage ring (168 orginally); Libera Brilliance + Libera Electron
References: Performance of the FOFB with DDBA in Diamond Light Source, IPAC2017, TUPIK113
Diamond Light Source Electron Beam Position Feedback: Design, Realization and Performance, ICALEPCS2009, THB003
Comments:For D-II, number of BPMs on storage ring increases to 252 and we intend to use pilot tone with analog front end in-tunnel and digital signal processing using mTCA platform in the Control and Instrumentation Areas [Diamond-II CDR ].
BPM system:192 Libera Brilliances and 128 Libera Sparks ERXR (iTech) for the Storage Ring
75 Sparks for the Booster
References:Strongly increased Performance and Functionalities of the ESRF BPMs with the Libera system (ESLS 2010)
Complete Test Results of New BPM Electronics for the ESRF New LE-Ring (IBIC2018)
Comments:SR Fast Orbit Feedback only using the 192 Brilliances (but work in progress to include the 128 Sparks)
General Discussion / Welcome
September 01, 2021, 09:01:48 AM
Welcome to the Beam Diagnostics Forum!

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