Space charge when splitting lattice into files

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astecjames
Posts: 5
Joined: 04 Apr 2014, 04:27

Space charge when splitting lattice into files

Post by astecjames » 30 Sep 2020, 12:45

Hi,

I have a beamline with a compressing dogleg, and some LSC-induced energy spread growth in the line *after* the dogleg, when I am at maximum compression. This is expected.
However, if I split my lattice into (say), DOGLEG.lte, POST-DOGLEG.lte etc. and track using the output of the previous lattice section as the input to the SDDS_BEAM command, I no longer see LSC-induced energy-spread in the post-dogleg section. All other parameters stay the same except the longitudinal ones, that would be expected to grow due to LSC. CSR and other effects are off (but do not change the basic result).
"Split" and "Single" Lattices are identical (combining all "Split" lattices, does give the "Single" lattice).

Is there something wrong with what I am doing? Or is there a method I can call to "fix" this?

I have included a plot, illustrating the issue (hopefully it is clear what is going on!). The location of the splitting between lattice files is highlighted.

Thanks for any help you can provide,
James
Attachments
split_single_lsc_problem.png

astecjames
Posts: 5
Joined: 04 Apr 2014, 04:27

Re: Space charge when splitting lattice into files

Post by astecjames » 02 Oct 2020, 04:18

Hi,

Apologies, but I have fixed my own stupidity here. I was using CSRDRIFTs (since I have a 2-dipole chicane), and the LSC works in the CSRDRIFT after the dipole in the SINGLE lattice case. In the SPLIT lattice, (since there are no dipoles in the POST-DOGLEG.lte) file, CSRDRIFTS do not work in terms of LSC. Changing the drifts to LSCDRIFTS and now I get the expected energy-spread increase.

However, another question: Is there any way to enable LSC for CSRDRIFTS even if there is no CSR-emitting elements in the lattice?
My code generates the lattices programmatically, and it's not trivial to switch between LSCDRIFT and CSRDRIFT only after a dipole (which is why I was using CSRDRIFT everywhere). I realise this is my problem and not yours, but... :lol:

Cheers,
James

michael_borland
Posts: 1794
Joined: 19 May 2008, 09:33
Location: Argonne National Laboratory
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Re: Space charge when splitting lattice into files

Post by michael_borland » 06 Oct 2020, 14:20

James,

My suggestion is to use the &transmute_elements command, as in

Code: Select all

&transmute_elements name=D*, type=CSRDRIFT, new_type=LSCDSRIFT &end
combined with &alter_elements to set any parameters you need on the LSCDRIFT elements, e.g.,

Code: Select all

&alter_elements name=D*, item=BINS, value=100 &end
--Michael

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