stupakov option in CSRDRIFT

[Philippe Piot]

Hello,
In a CSRDRIFT located just downstream of the four )last) bend of a standard chicane, I noticed that the energy spread continuously increases with the stupackov=1 option (i.e. it does not seem to taper off). In fact, arbitrarily increasing the drift length results in a larger energy spread (if I increase the length of dfinal in the attached .lte file). The toy example attached is essentially modified from the bunchCompressor example. My understanding is that the stupakov=1 option does include an attenuation of the wake (though I could not find a paper describing the model). Thank you, -- Philippe.

[michael_borland]

Philippe,

I do expect the effect to drop off with distance, but the rate should depend roughly on the overtaking length. You could check this for your case to see if it is long.
https://journals.aps.org/prab/pdf/10.11 ... B.4.070701

I extended your simulation as follows

Code: Select all

bl: line=(q,linac, chicane,500*dfinal)

then plotted Sdelta vs s using the .sig file. I get a plot wherein the energy spread increases, levels off, then begins to drop.

chicaneRun.png (10.44 KiB) Viewed 3505 times

Perhaps the wake is not only slowly diminishing in intensity, but the electron beam is slipping relative to the wake. The attached animation, showing the change in momentum for each DFINAL element, seems to support this. The bunch distribution has a strong spike, which may not be modeled well if the bin size is too large.


The Stupakov model is in
http://www-ssrl.slac.stanford.edu/lcls/ ... -01-12.pdf

--Michael