Abstract
We present a new symmetry-based concept for an achromatic low-beta collider interaction region design. A specially designed symmetric chromaticity compensation block (CCB) induces an angle spread in the passing beam such that it cancels the chromatic kick of the final focusing quadrupoles. Two such CCBs placed symmetrically around an interaction point allow simultaneous compensation of the 1st-order chromaticities and chromatic beam smear at the IP without inducing significant 2nd-order aberrations to the particle trajectory. We first develop an analytic description of this approach and explicitly formulate 2nd-order aberration compensation conditions at the interaction point. The concept is next applied to develop an interaction region design for the ion collider ring of an electron-ion collider. We numerically evaluate performance of the design in terms of momentum acceptance and dynamic aperture. The advantages of the new concept are illustrated by comparing it to the conventional distributed-sextupole chromaticity compensation scheme.
Highlights
In order to achieve the highest possible luminosity in a collider [1,2], the colliding beams must be focused to a small spot at the interaction point (IP)
A specially designed symmetric chromaticity compensation block (CCB) induces an angle spread in the passing beam such that it cancels the chromatic kick of the final focusing quadrupoles
We proposed a new symmetry-based interaction region concept for a high-luminosity collider ring design
Summary
In order to achieve the highest possible luminosity in a collider [1,2], the colliding beams must be focused to a small spot at the interaction point (IP). The size of the required beam expansion is determined by the desired degree of beam squeezing at the IP and the focal length of the FFB, which is closely related to the space between the IP and the nearest focusing quadrupole. A commonly used chromaticity compensation technique is to install same-strength sextupoles in pairs with ÀI (minus the identity) transformation between them to cancel their nonlinear kicks [3,8] This approach does not treat all of the sextupole-induced 2nd-order effects. The symmetries of the beam orbital motion and dispersion combined with a symmetric quadrupole and sextupole arrangement in the CCBs allow simultaneous compensation of the 1st-order chromaticities and chromatic beam smear at the IP without inducing significant 2nd-order aberrations and helping preserve the ring’s dynamic aperture. The IR design is mirror symmetric with respect to the IP
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