| Magnet Unit(s) | PR02 8042 |
|---|---|
| Typical BDES | 57.654 kG |
| Typical Current | 150 A |
| Typical PS Voltage | 20 V |
| Nominal Beta X | 85 m |
| Nominal Eta X | -0.05 m |
| Nominal Beta Y | 11 m |
| Nominal Eta Y | -0.05 m |
HER QF7R is part of the collision straight focusing scheme for generating small IP beta functions.
The HER collision straight focusing scheme is basically symetric in Z with respect to the collision point.
Starting at end of arc 1 (z = -62 m) and progressing in the HER beam direction towards the IP the HER focusing elements progress in the following sequence:
There is a long (~14m) drift after the last arc magnet QDS0L. In this drift the betax value increased and the betay value gradually decreases.
QF7L (z = -46m) turns around the betax function (betax starts decreasing) and betay starts to increase.
Shortly after QF7L is QD6L (z = -44m). QD6L causes the betax function to start to increase again while betay decreases. QF7L and QF6L can be thought of as a quad doublet.
After this doublet there is another long (35m) drift. In this drift the betax function continues to increase dramatically and the betay function comes to a waist and then also starts to increase.
Both betax and betay increase after this drift up until QF5L (z = -7.6m). QF5L strongly turns around the (huge) betax function and leaves betax rapidly decreasing as betay increases further.
Just after QF5L is QD4L (z = -5.3m). QD4L strongly strongly turns around the betay function and leaves betay rapidly decreasing while betax is decreasing also (although not as rapidly as between QF5L and QD4L).
The HER beam then traverses the field free region of the LER Q2 septum quadrupole after which point the two beams share the same magnet elements.
QD1 is a permanent magnet inside BaBar (z = - 1.8m) which further focuses in the vertical plane while allowing betax to continue to decrease as well. The HER beam is "on-axis" in QD1 while the LER is horizontally offset (LER outgoing in this incoming HER perspective) by about 3 cm. The permanent magnet dipole B1 (z = -0.3m) then bends both beams onto the same trajectory for collision at the IP (z = 0.0m). This scheme allows for the small collision point beta function values of 0.5m horizontal and 0.012 m vertical.
Since the HER collision straight is basically symeteric about the IP, the outgoing focusing sequence is basically the same as the incoming sequence in reverse.