model of ring by several ilmatrix elements？

[li.chao]

Dear Michael ,

I am modelling a storage as two ILmatrix elements and the twiss parameters of there two ilmatrix elements are the same.
For a test set, I keep dispersion, dispersion prime and chromaticity to zero for simplicity.
Then I have two lattices as
lattice A: ring = ilmatirx
lattice B: ring = (ilmatirx1, ilmatirx2)
and conditions as nu1 + nu2 = nu, L1 + L2 = L are met,
where nu1,nu2, nu are working point of the ilmatirx1, ilmatirx2, ilmatirx respectively.
In the attached elegant files, the definition of the lattice can be found there.
I expect latticeA and latticeB produce the same tracking results, where as they does not.

Through the results I found two things:
1. in lattice latticeB, the particle longitudinal phase space (dt,p) slowly shift to the positive side.
2. the bunch length from these two lattice does not agree.

Would you please help to figure out which part of my files are wrong?

yours Chao

[michael_borland]

Chao,

I think it is just the L parameters on your ILMATRIX definitions are not quite right. If I add ILMAT1.L and ILMAT2.L, I get 2303.999099999, not 2304.

--Michael

[li.chao]

Dear Michael,

Thanks for your reply. I realized that I probably asked wrong questions in my last post. To make less confusion, I deleted the last post and summarize my question in this post. The question is in elegant computing, what these two elements (ibsscatter and TSCscater) do to affect particles.

1 IBSCATTER element
Ref. to this paper https://journals.aps.org/prab/pdf/10.11 ... B.8.081001.
I would like to know if IBSCATTER did the similar calculation as shown in the paper above. 1) from the ith IBSCATTER element to (i+1)th element, with the lattice function in between get the ibs growth rate, Eq.(4). 2) take the transient beam parameter from tracking at the ith IBSCATTER element as initial value to solve the Eq(1)~Eq.(3) to get the beam parameter at (i+1)th IBSSCATTER element. 3) The beam parameters given by IBSCATTER actually stores the value obtained from step 1) and 2). Is it? If so, how to connect beam emittance from IBS effect to value from beam distribution (rms emittance)? If it is not, would you mind to correct me and explain a little bit more?

2 TSCATTER,
It seems like that this element can not be used together with beam tracking. The touschek_scatter command let code track particles whose dp>dp_m, of course taking the touschek scattering effect at TSCATTER element. The simulation repeats n times, where n is the number of TSCATTER elements. In this sense, the loss rates at these TSCATTER element can be found.

Please correct me or give me some more comments. Will be very helpful for a better understanding and looing forward to your reply.

Thanks again.
yours Chao

[michael_borland]

Chao,

The IBS simulation method is summarized in
https://accelconf.web.cern.ch/IPAC2015/ ... pma012.pdf
The calculation of the emittance growth rates is based on Piwinski's method. This is computed in segments of the lattice and then applied to the particle distribution either as random scattering or a smooth inflation factor. If tracking is carried out for many damping times, the beam will come to an equilibrium between IBS and quantum excitation on the one hand, and radiation damping on the other. If you just want to quickly compute the equilibrium, use the program ibsEmittance.

It is correct that the TSCATTER element can't be used for ordinary tracking. It is only used to determine loss rates and locations. More details are in https://journals.aps.org/prab/abstract/ ... .13.074201

--Michael

[li.chao]

Dear Michael

Thanks for your explanation. I also checked the elegant source code about the IBS and TScatter element.
As you described, it is clear.

Thanks again.
yours Chao