Re-optimization of the Final Focus System Optics with Vertical Chromaticity Correction*

The purpose of the final focus system (FFS) of the future linear colliders (ILC and CLIC) is to demagnify the beam to the required size at the interaction point (IP). This can be done in a compact way based on a local chromaticity correction [1]. For an enlarged horizontal beta function at the IP βx*, chromaticity on horizontal plane will be smaller. We get a smaller vertical beam size, at the expense of a larger horizontal beam size, with chromaticity correction mainly in the vertical plane using fewer sextupoles: 2 or 3 instead of 5. For a new FFS design with this scheme, we’ll also not need the first peak of β, which will reduce overall vertical chromaticity. This can lead to a shorter and easier to tune FFS. Another benefit is that the beamstrahlung at the IP will be reduced.