A warning appeared when finding DA

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Bingfeng
Posts: 1
Joined: 20 Oct 2020, 07:38

A warning appeared when finding DA

Post by Bingfeng » 20 Oct 2020, 22:11

Hello Michael and all,
I used the "n-line" mode to find aperture. But there is a warning appeared in some lines:
Warning: particle acquired undefined slopes when integrating through kick multipole.
And the other lines don't have this warning. I want to know what happened in those lines and whether it will affect my results.
I attached my .ele and .lte files below, Thanks for your help.
Attachments
findaper.ele
(776 Bytes) Downloaded 250 times
lattice.lte
(1.85 KiB) Downloaded 244 times

michael_borland
Posts: 1735
Joined: 19 May 2008, 09:33
Location: Argonne National Laboratory
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Re: A warning appeared when finding DA

Post by michael_borland » 21 Oct 2020, 09:05

Bingfeng,

The warning is sometimes seen when a particle is being propagated through a magnet (usually CSBEND, KQUAD, or KSEXT). It indicates that when applying kicks in the integration an exception was encountered in computing the slope; it suggests that the particle got turned around. This may result from limited accuracy in the integration, which becomes more of an issue when positions and momenta are large. It also indicates that with nonlinear elements (sextupoles and avoid), large positions can result particles seeing very large fields and hence very large kicks, a result of unphysical extension of the multipole field to arbitrarily large coordinates. It is more likely to be seen if N_KICKS is too small, but that's not the case for your run.

This is more likely to happen when running DA without any physical apertures, since in that case particles are only eliminated when they reach very large amplitudes (elegant has a built-in limit at 10m) or acquire unphysical slopes. For example, if I insert a MAXMAP element that limits the amplitudes to 0.1 m, the messages don't appear.

Bottom line: I wouldn't worry about it as long as N_KICKS is reasonably high.

--Michael

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