6.3.1 Far-Backwards Lattice

[simonge]

Briefly, what does this PR introduce?

Originally instigated by moving the B2eR magnet out of the cryostat, this geometry matches the most recent lattice of the accelerator in the far backward region.

What kind of change does this PR introduce?

• Bug fix (issue #__)
• New feature (issue #__)
• Documentation update
• Other: __

Please check if this PR fulfills the following:

• Tests for the changes have been added
• Documentation has been added / updated
• Changes have been communicated to collaborators

Does this PR introduce breaking changes? What changes might users need to make to their code?

No

Does this PR change default behavior?

Changes the path of electrons in the far-backward region. This will break the Low-Q2 Tagger reconstruction, simple retraining of the network should be sufficient after this is eventually merged.

[simonge]

@nat93 @adamjaro Please could you check the quadrupole fields have been calculated correctly from the tables, I don't think the x/y divergence plots I see quite match those you both previously shared.
https://github.com/eic/epic/blob/6.3-Lattice/compact/fields/beamline_18x275.xml#L22

[ajentsch]

@simonge have the quad fields been confirmed yet? I will approve once your question has been answered by either @adamjaro or @nat93 to make sure things are correct.

[ajentsch]

@simonge have the quad fields been confirmed yet? I will approve once your question has been answered by either @adamjaro or @nat93 to make sure things are correct.

Also, you may need to pull the latest version of epic because there are some new magnet XML files I put together. I made some new changes today. You should wait until those are approved, and merged, and THEN pull that new version in, and add your changes to the additional XML files for the magnets.