Design of optics for the Final Focus Test Beam at SLAC

The goal of the Final Focus Test Beam experiment (FFTB) is to produce an electron beam spot of 1 μm by 60 nm in transverse dimensions. Considering its future application to the TLC (TeV Linear Collider) the beam optics are designed so that the beta functions and the pole-tip field of the final quadrupole are the same as the TLC parameters. Previously, a very flat beam was regarded as suitable for the TLC. Thus, a method with single-family sextupoles was sufficient to correct the chromaticity. Recent studies however, reveal that e⁺ e^--pair productions during beam collision generate a huge amount of background. In order to get out of the background, the `crab-crossing´ scheme is necessary. As a result, the optimum aspect ratio of the beta functions is reduced to less than 100, and chromaticity corrections for both planes become inevitable. In the design chosen, a new chromaticity correction scheme with noninterlaced two-family sextupoles is used. Optimization of the system is described, and tolerances and tuning methods are considered