Author Topic: Back-end for longitudinal feedback system  (Read 302 times)


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  • Institute: Synchrotron-light for Experimental Science and Applications in the Middle East
Back-end for longitudinal feedback system
« on: July 02, 2022, 02:32:20 PM »
Dear Experts,
This Nashat Sawai from SESAME synchrotron, it is first time posting here  :D
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

Benoît Roche

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Re: Back-end for longitudinal feedback system
« Reply #1 on: July 19, 2022, 05:05:49 PM »
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.