IBSCATTER with ILMATRIX gives wrong Horizontal Emittance

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IBSCATTER with ILMATRIX gives wrong Horizontal Emittance

Post by astecjames » 12 Apr 2021, 10:20


I am trying to model a ramping booster using an ILMATRIX + SREFFECT element with IBS effects included via the IBSCATTER element.

In all cases I have tried, the horizontal emittance seems to scale, if at all, inversely proportional to the bunch charge. If I track using element-by-element tracking I get the expected scaling.
Strangely, the vertical and longitudinal emittance scale correctly. This is also true if I include COUPLING in the SREFFECTS element.

I have included an example of the ILMATRIX based tracking, and a few pictures, comparing the ILMATRIX (dashed lines) vs. element-by-element (solid lines) tracking, to show the scaling going wrong only for the horizontal plane.
I tried moving around the order of the elements, but nothing seems to change the results.

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Re: IBSCATTER with ILMATRIX gives wrong Horizontal Emittance

Post by michael_borland » 21 Apr 2021, 16:10


I would not expect IBSCATTER to work with ILMATRIX, since IBSCATTER needs to perform integrals over the lattice to get the IBS growth rates. Sorry that the code doesn't detect this situation. Some day I hope to solve it. Probably the best approach for now is to use linear matrices or, if you have the computing power, element-by-element tracking.


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