| Magnet Unit(s) | PR08:2012 PR08:4012 |
|---|---|
| Typical BDES | -18.354 kG |
| Typical Current | 70 A |
| Typical PS Voltage | 55 V |
| Nominal Beta X | 4.7 m |
| Nominal Eta X | 0.33 m |
| Nominal Beta Y | 25 m |
| Nominal Eta Y | 0.0 m |
QD4I is a member of the family of quadrupoles in straight 8 which generate the special lattice conditions required for the injection region.
LER injects in the vertical plane. In order to reduce the challenge of septum and kicker strength, it is desirable to achieve a large vertical beta function at the location of the injection septum. The lattice in straight 8 is designed to achieve a betay=200m at the injection point.
The quadrupoles in straight 8 are powered symetrically in Z about the injection septum which lies at the straight's midpoint.
The method employed to make this large vertical beta function is as follows:
As the lattice progresses out of arc 9 into the injection straight there is a standard QD/QF/QD triplet. These magnets are called QD4I, QF0I and QD0I. These three magnets are slightly weaker than an ordinary straight quadrupole. Following this triplet the cell length (spacing between quadrupoles) doubles, allowing the beta functions to increase.
About half way from QD0I to the straight's midpoint there is a QF called QFI. QFI turns around the (at this point large ~100m) betax function and causes the betay value to grow rapidly.
Just before the septum at the straight's midpoint the next element is QDI which turns around the large betaY but is sufficiently close to the septum to achieve the desired large betay at that location.
The QDI pair are pushed sufficiently close to the septum that the separation either side of the septum is small (~ 4m). This allows the pair to be thought of as a single QD element (two QDs in a row is unusual) and the two magnets are often refered to as QDIA and QDIB.