Optical design of the CEBAF beam transport system

Abstract

Modifications to the Continuous Electron Beam Accelerator Facility (CEBAF) beam transport system design are described. These include detailing of injector optics and inclusion of an isosynchronous injection chicane in order to avoid bunch lengthening during injection, use of a 'staircase' spreader/recombiner design in order to reduce error sensitivity, use of 1 GHz RF separators for separation and extraction of multiple beams to reduce emittance dilution, and modification of the beam transport system to accommodate a fifth recirculation of the beam. The isochronicity of the injector chicane design and the choice of a lower frequency for the RF separator extraction system have made the machine phase space design values inherently more achievable. The staircase spreader/recombiner design has reduced sensitivity to lattice errors by a factor of two. This gain in reduced sensitivity is offset by the increased lattice error sensitivity of the five-pass design over that for the previous four-pass design. >