| Magnet Unit(s) | 3142 |
|---|---|
| Typical BDES | -3.9994 kGm |
| Typical Current | 120 A |
| Typical PS Voltage | 35 V |
| Nominal Beta X | 37 m |
| Nominal Eta X | -0.62 m |
| Nominal Beta Y | 3.7 m |
| Nominal Eta Y | -0.006 m |
LER BCC4 is part of the collision straight bending scheme.
LER straight 2 is not straight, nor is it flat.
The "S" shaped horizontal bending scheme of the LER straight 2 arises from the need to separate the beams at the IP using bending magnets.
Four permanent magnets inside BaBar achieve this separation. B1 dipoles (at z = +/- ~0.3m) bend the two beams differently (due to their different energies) to achieve this separation. Further, QD1 quadrupoles (at z = +/- 1.8m centered on the HER trajectory) further deflect the LER beam due to the LER's ~3cm off axis trajectory at the QD1 magnets.
Matching to this near IP LER x trajectory is done with an S-Bend geometry.
Beginning inside LER incoming arc 3, this S-bend geometry is achieved using the following magnet scheme:
Just after the last ordinary arc 3 bending magnet an IR2 local dipole BBM1 at z=-63m from the IP bends the LER beam horizontally inward. This inward trajectory continues until z=-47m where dipole BCC4 bends the beam back parallel to the horizontal straightline between arc end points. At this point the beam is offset ~2.8 meters inboard. At z=-30m the beam is bent again back outward by dipole BCC1 and continues towards the centerline.
At z=-19m with LER/HER horizontal separation about 0.8m another (pair of) dipole(s) BCX2 bend the LER beam back outward but not enough to be parallel. From this location the LER beam points nominally towards BaBar.
Once inside BaBar, the LER beam is bent back (nearly straight) again by the inward QD1 quadrupole and B1 dipole, and overlaps the trajectory of the HER. The outward B1 and QD1 then deflect the LER towards the outboard side (away from the center) of the ring and a symetric scheme is used to complete the "S" bend geometry into arc 1.