Abstract
Two dipole doglegs are widely used to translate the beam axis horizontally or vertically. Quadrupoles are placed between the two consecutive dipoles to match first-order dispersion and provide betatron focusing. Similarly, a four dipole chicane is usually employed to form a bypass region, where the beam axis is transversely shifted first, then translated back to the original axis. In order to generate an isochronous section, quadrupoles are again needed to tune the first-order transfer matrix element ${R}_{56}$ equaling zero. Usually sextupoles are needed to correct second-order dispersion in the bending plane, for both the dogleg optics and the chicane (with quad) optics. In this paper, an alternative optics design is introduced, which is based on a simple FODO cell and does not need sextupole assistance to form a second-order achromat. It may provide a similar function of either a dogleg or a bypass, by using two or four of such combined supercells.
Highlights
A transverse dogleg beam line or a bypass beam line is needed for many accelerator systems from the requirement on shifting the beam axis in some region, which is sometimes due to realistic constraints
In the 1970s, Brown developed a systematic approach to design secondorder achromats from investigating matrices formulas [1], which uses at least four identical cells with dipoles, quadrupoles, and sextupoles and can eliminate all geometric and chromatic terms up to second order. Wan developed another approach with Lie algebra to design achromat to arbitrary order, taking advantage of the midplane symmetry and using multipole magnets for each order [2]
Sextupole magnets implies a strict tolerance on the beam line alignments. In many of these beam lines, the electron beam is transported with a large energy spread which is in the percent level
Summary
A transverse dogleg beam line or a bypass beam line is needed for many accelerator systems from the requirement on shifting the beam axis in some region, which is sometimes due to realistic constraints. Wan developed another approach with Lie algebra to design achromat to arbitrary order, taking advantage of the midplane symmetry and using multipole magnets for each order (for example, octupoles for third-order achromat) [2] These systems are designed with dipoles, quadrupoles, and sextupoles, to zero both first-order and second-order dispersion in the bending plane, and to provide an isochronous transfer system in the bypass case. A FODO cell based optics design is described which eliminates the use of sextupoles In one supercell, both the first-order (R16 and R26) and second-order dispersion (T166 and T266) terms are closed, which guarantees no chromatic emittance growth as the beam transports through this section. Macroparticle tracking simulations have been performed in the code ELEGANT [3], to evaluate the property of this optics design
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