The beam optics after dipole is incorrect if a entire beamline model with degrader is adopted

[曾宪虎]

If a degrader is located in the beamline, the beam optics after dipole is not correct. And the energy spread is also incorrect which is decreased by the energy slit. But if I divide beamline into two parts (one part only inculdes quadrupole and degrader, another part inculdes dipole behind degreader), then the beam optics is correct. wherein, the input beam of second part is based on first part with a sampler. Therefore, I guess there are some bugs in BDSim.

Looking forward to your early reply.

Thanks,

Xianhu

[Laurie Nevay]

Dear Xianhu,

Are you using the ‘scaling’ parameter for the dipole afterwards? And, can I assume you’re also using a sub-relativistic beam (ie lorentz beta < 0.95)?

In v1.3.3 there is a bug where the dipole tracking algorithm did not scale properly with sub-relativistic beams. Also, the dipole fringe fields did not scale properly. These problems have since been fixed but a release has not been made yet. For now, I recommend checking out v1.4-rc - our current “release candidate”. It’s almost about to be released and works well.

Best,

Laurie

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[Laurie Nevay]

Offline we found that the degrader could cause geometrical overlaps when over half closed. This has since been fixed. Going through testing just now with Xianhu. v1.4 has also been released now which should fix the scaling issue with the dipole fringes.

[Laurie Nevay]

I think this is resolved now. We have repeated extensive testing on the dipole fringe fields.