Charge studies

[simona.bettoni]

Dear all,
I would like to simulate the change of the beam parameters when I vary the charge of the machine having RF structures, a compressor, and other structures.

I optimized 3 linacs (L1, L2, HE) in cascade, each of them with some difference (at least in the previous phase of the design), and at the end a chicane and other structures (EC). If I run the models seprately using the final distribution of a section as the starting one of the following one:
L1
L2
HE
and HE + EC
I see very reasonable numbers in term of final bunch length and energy spread.

The problem is that now I would like to fix the machine at the setting of 5 nC, and see what happens to the beam at much lower charge (ideally 0 pC, but let's say few pC to be physical).

At the beginning I tracked the distribution with the different charges down to the entrance of EC (where the fiducialization will play the major role), but the problem is that I should say to Elegant: "Run with the charge Q_nominal and set the machine, keep the machine, and use another distribution and not only a different charge without altering the machine settings."

I tried then something different: I composed a model with the three linacs in cascade and I added the EC. I used then &vary_element to change the charge. When I try to run it, I see that the simulation crashes because the bunch length is longer than the wakefield already also for the Q_nominal, and I do not understand why.

Could this check on the charge may be done in a smarter way? Giving to Elegant for each charge also a different initial distribution coming from the upstream linacs (beam loading different so different chirps)? Is ok the procedure of the full model? Something I missed?

I upload the files, so that it is possible to see what I am doing.

Thanks a lot for any suggestion,
Simona.

[simona.bettoni]

Correct version of the files attached.

[simona.bettoni]

I solved the issue. It was simply a wakefield file which was defined in a small range of time. All good.
Kind regards,
Simona.