LER SK6L (PR02 LGPS 201)

Lattice Description

SK6L is one of a family of twelve local skew quadrupoles (SK6-SK1,SK1L-SK6L) for the LER interaction point.

Skew quadrupoles introduce coupling or rotation. Like all quadrupoles, the (deflecting) field gradient is uniform across position in the quadrupole magnet's field. An upright quadrupole provides an X or Y deflection proportional to X or Y offset, with no Y deflection dependance upon X position and vice versa. A skew quadrupole (upright quadrupole rotated 45 degrees) provides X and Y deflection each of which varies with both X and Y offset.

LER has two families of skew quadrupoles: Global and IR2 local.

Global skew quadrupoles are intended to be used to tune away (cancel) unintended sources of coupling or rotation (upright quadrupole roll errors and nonzero vertical trajectory in sextupole magnets).

IR2 local skew quadrupoles are intended to be used to cancel beam rotation caused by the design off-axis and dispersive trajectory through the BaBar solenoid field.

The IR2 local skew quads are located symetrically in Z about the IP, as their names would indicate.

The SK6 and SK5 skew quads are out in the arcs, and largely couple the large arc horizontal dispersion into the vertical plane. LER SK6 and SK5 magnets are not disrete magnets, rather they are trim windings on the SCY3 sextupoles.

The SK4 through SK1 skew quads are discrete magnets within the "straight" part of IR2. However; since there is both horizontal and vertical bending in LER associated with the IP collision/separation scheme, it is difficult to assign geometric vs. dispersive roles to the LER local skew quadrupoles.

While SK4 through SK2 are "ordinary" electromagnets, the SK1 magnets are permanent magnets due to space constraints being so close to the interaction point at z= 3 m from the IP...just outboard of QF2. The SK1 skew quadrupole strength adjustment is achieve by rotating the permanent magnet assembly; trading the relative amplitudes of upright vs. skew quadrupole strength.