Sbend overlapping

[Hayg Guler]

Dear all,

we are running bdsim for new machine (ERL, Perle @ Orsay) and we face some error coming from element overlapping.

Element definition in gmad file :

BCHICC_0: sbend, angle=-0.2617993878, fint=0.0, fintx=0.0, hgap=0.0, l=0.151727274;

error message :

Error: the combination of length, angle and horizontalWidth in element named "BCHICC_0" will result in overlapping faces!
Please reduce the horizontalWidth

Thanks

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[Laurie Nevay]

Hello Hayg,

Thanks for posting an issue. By default, the horizontalWidth parameter is 0.5 m. This is controllable as an option acting as a default for all elements if not specified. It’s also controllable with the same parameter in the element definition. So:

option, horizontalWidth=0.3*m; 

will be the default for all elements (not just sbends). And

BCHICC_0: sbend, angle=-0.2617993878, fint=0.0, fintx=0.0, hgap=0.0, l=0.151727274, horizontalWidth=0.3*m;

would be used to just specify that single sbend. Any parameter specified in an element definition supersedes the default from the corresponding option.

In your case, the angle for the bend is quite high relative to the length of the sbend. The code correctly points out that we can’t make a bend of this length and angle as well as be the default 0.5m without the front face and back face crossing each other. The default geometry for an sbend is a C-shaped yoke with the yoke on the inside of the bend (all controllable). If you specify a smaller horizontal width it will work. The picture below is with horizontalWidth=0.3*m.

Also, feel free to email me (laurie . nevay @ cern.ch) if you want to discuss about using BDSIM for PERLE - would be happy to discuss.

Cheers,
Laurie

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