Elegant users forum

Hello,

I'm confused about some tracking results.We generate initial particles with gaussian distribution,ultra-low emittance 80pm,0.4% energy spread,etc...Then we let the particles pass through a simple DBA,the horizontal phase space is very odd.However,when we change the elements CSBEND to SBEND,KQUAD to QUAD,and default_order=1 in run_setup,the result seems to be better.After communicating with others,we think the element KQUAD and CSBEND may produce chromatic-like effect on the emittance. Could you explain this two different results?

Thanks!

Tian

Tian,

The &sdds_beam command in your .ele file references beam_A.out, which you didn't provide. I used the initial particle file you provided instead.

I found several problems with the tracking setup, having to do with not specifying the "N_KICKS" parameter on the CSBEND, KQUAD, and KSEXT elements. The defaults are rarely sufficient and it up to the user to set these appropriately. For your case, I suggest 100 for CSBEND, 30 for KQUAD, and 10 for KSEXT.

The other issue is that the beamline has non-zero chromaticity, so a beam with non-zero energy spread is expected to grow in emittance. Of course, using first-order matrix based tracking will not show this.

--Michael