Elegant users forum

Dear all,

I have a problem about simulations concerning the vertical spot size at a screen, placed after a RF deflector. The problem is explained in detail in the annex "question.pdf".

Thank you for your attention and for any help you can provide.
Best regards,
Luca

Luca,

My first guess is that the problem comes in equation 2. This is only correct if <y t> = 0 and <y' t> = 0. I suggest checking whether these conditions hold by putting a WATCH element upstream of the RFDF element.

I can look into it further if you supply the file pls_LoEm_new_gun_80MeV.sdds .

--Michael

Dear Michael,

in annex the file "pls_LoEm_new_gun_80MeV.sdds".
I have already checked the condition that <y t> and <y' t> have to be negligible (see the annex "correlations terms.pptx").

Luca

Luca,

To simplify the comparison, I used your second example with bunched_beam and sdds_beam. I find that I get essentially identical results, but they are different from yours. I used sddsanalyzebeam to give me the sigma matrix for the beam file, then used the results of that analysis to configure bunched_beam. In particular, I included the energy chirp. See the attachment.

At this point, my suggestions are: 1) Used bunched_beam in the more complicated simulation to get a cleaner comparison to theory. It may be that the initial energy chirp or energy chirp acquired from wakefields etc. matters. 2) eliminate components of the simulation (e.g., CSR, wakes, acceleration) until you identify the source of the discrepancy.

--Michael

Dear Michael,

the problem was that I didn't include the energy chirp in my bunched beam.
Moreover, equation 2 is correct when energy chirp is negligible, but in this case it doesn't true. Therefore, in equation 2 there should be other terms (not negligible) depending on energy chirp.

Thank you for your suggestions and help,
Luca