Recycler Chromaticities and End Shims for NOvA at Fermilab

TL;DR

This paper presents a redesigned lattice for the NOvA Recycler ring at Fermilab, optimizing chromaticity correction and beta-functions through end shim modifications to improve beam injection and stability.

Contribution

It introduces a novel end shim design for permanent magnets that achieves desired chromaticity and tune requirements with feasible quadrupole strengths and reduced beta-functions.

Findings

Successfully redesigned end shims meet chromaticity and tune goals.

Reduced maximum beta-functions from 80 m to 55 m.

Validated beam injection scenario via dynamic aperture tracking.

Abstract

In era of NOvA operation, it is planned to slip-stack six on six Booster proton batches in the Recycler ring for a total intensity of 5 1013 protons/cycle. During the slip-stacking, the chromaticities are required to be jumped from (-2,-2) to (-20,-20). However, they can only be adjusted to (-12,-12) from (-2,-2) using existing 2 families of powered sextupoles. On the other hand, the presently designed Recycler lattice for Nova replaces the 30 straight section with 8 D-D half FODO cells . We use 3 quads in a half-cell to obtain the working point under the limit of the feasible quad strength, and the maximum beta-function in this section cannot be less than 80 m. In this paper, we re-designed the end shims of the permanent magnets in the ring lattice with appropriate quadrupole and sextupole components to meet both chromaticity and tune requirements. We are able to use 2 quads in a half cell in RR30 straight section within feasible quad strength. The maximum beta-functions are also lowered to around 55 m. The dynamic aperture tracking has been done using MAD to simulate the scenario of beam injection into the Recycler ring for Nova.