Achromatic Low-Beta Interaction Region Design

To reach high luminosity in a collider, its beam must be focused into a small-size spot at the interaction point (IP). Achieving such a small focal spot size requires expanding the beam to a rather large size at the final focusing quadrupoles. This is space consuming and leads to large chromaticity and chromatic beam smear at the IP. Compensating these chromatic effects proved challenging because the conventional approach of using sextupole families introduces 2nd- and higher-order beam aberrations at the IP and significantly limits the colliders dynamic aperture. A new concept for an achromatic low-beta interaction region (IR) design is being developed, in which the number of aberration compensation conditions at the IP is greatly reduced by requiring certain symmetries of the beam orbital motion and of the dispersion and by using a symmetric arrangement of quadrupoles, sextupoles, and octupoles. Such a scheme allows simultaneous compensation of the 1st-order chromaticities and chromatic beam smear at the IP without inducing significant 2nd-order aberrations and therefore largely preserves the dynamic aperture. In order to reduce the IR space requirements, it is proposed to install all or most of the IR components in the bending arcs. An analytic theory for the aberration-free low-beta spatially-compact IR insertion will be developed into a publishable paper. Based on the analytic findings, a specific IR design with compensation of the nonlinear effects up to 3rd order using sextupole and octupole magnets will be proposed. Initial numerical studies of the design will be performed to verify the analytic results. Dynamic aperture, momentum acceptance, and error sensitivity studies will be initiated for comparison to other IR designs. A preview of topics to be explored in Phase II will be carried out.Commercial Applications and Other Benefits: This new approach would allow more aggressive designs of the beam focusing systems for the interaction regions of particle colliders. The resulting greater feasibility and discovery potential of such colliders would make their construction more likely. Existing colliders can also benefit from the technology that will be developed in this project.