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
Horizontal phase space distortion with KQUAD
Moderators: cyao, michael_borland
Horizontal phase space distortion with KQUAD
- Attachments
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- arc_new_dba.lte
- (2.22 KiB) Downloaded 282 times
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- beam_A.out
- initial particles
- (1.98 MiB) Downloaded 285 times
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- pass_dba.ele
- (1.01 KiB) Downloaded 316 times
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michael_borland
- Posts: 1933
- Joined: 19 May 2008, 09:33
- Location: Argonne National Laboratory
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Re: Horizontal phase space distortion with KQUAD
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
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