HER SQ2L (PR02 LGPS 5203)

Lattice Description

SQ2L is one of a family of eight local skew quads (SQ4L-SQ1L and SQ4R-SQ1R) for the HER interaction point.

Skew quads 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.

HER 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 SQ3 and SQ4 skew quads are out in the arcs, and largely couple the large arc horizontal dispersion into the vertical plane. This is intended to match the vertical dispersion generated by the horizontal bending of the HER beam inside the BaBar solenoid. Additionally, four strong sextupole magnets (SD2A and SD4A) have a deliberate mechanical offset in order to introduce skew quadrupole terms SK5 and SK6. For the HER, these deliberate skew terms have no "magnet like" adjustment, but adjustment can be achieved by changing the orbit in these sextupoles.

The SK1 and SK2 skew quads are within the "straight" part of IR2, and are intended to cancel the geometric (i.e. non-dispersive) rotations caused by the off axis horizontal trajectory in the BaBar solenoid.