Elegant users forum

Hello,

I have run elegant to correct a trajectory along the linac. Installation errors of all components — including bends, quadrupole magnets, RF cavities, and BPMs — have been considered in the simulation. My concern is how to properly handle BPM-related errors. When BPM installation errors are taken into account, the orbit position measured by the BPM includes not only the actual beam offset but also the error introduced by the BPM misalignment itself.Before performing trajectory correction, should I do anything with the BPM errors (which are randomly generated based on a Gaussian distribution, RMS 0.5 mm)? When I perform trajectory correction (one-to-one) directly with BPM errors included, the beam emittance increases significantly after correction(from 0.5 mm·rad to 1.2 mm·rad). How can I mitigate the emittance growth caused by BPM misalignments during correction?

Thank you very much for your help!
Best,
Zhenbiao

Zhenbiao,

Operationally, the way to handle this is to perform beam-based-alignment (BBA) so that you know the BPM offsets relative to nearby quadrupoles. In a simulation, you can mock this up by assuming that the BPM offsets are small. How small is determined by the anticipated accuracy of the BBA.

--Michael