Recent Progress in Muon Collider Storage Ring Lattice Design P. Snopok, C. Johnstone Abstract— A new lattice for a Muon Collider storage ring with a design collision energy of 750 on 750 GeV will be discussed. The important building blocks of the lattice: the Final Focus Section, the Chromatic Correction Section and the Arc Module are described in detail. These components of the collider have been designed keeping in mind that the storage ring must approximately match the footprint of the Tevatron Ring in order to take advantage of existing services and tunnels. The model presented here relies heavily upon a previous, highly optimized 50×50 GeV storage ring lattice design. The current design value for β * is chosen to be 1 cm, which has the advantage of lower chromaticities and longer bunch lengths (due to the hour-glass effect) as compared to the previous standard lattice with a β * of 3 mm. I. I NTRODUCTION The idea is to design a lattice for the storage ring that fits or matches approximately the footprint of the Tevatron Main Ring tunnel with all its bends and straights. Taking into account the current status of the Tevatron project, Muon Collider might be a logical next step in utilizing the existing tunnel with its infrastructure, thus saving a large amount of expenses connected to building a new accelerator complex for muons. II. MAGNET STRENGTHS Currently we use 50% dipole packing fraction, which results for the arclength of 5.85 km (6.28 km - 432 m of straights) in the dipole field of 5.3 T. At 750 GeV the magnet strengths are reasonable, in fact, the ultimate energy might be up to 1×1 TeV. III. 50×50 GEV LATTICE We use the 50 × 50 GeV lattice [1], [2] as a baseline, and scale its components to 750 GeV according to the scheme in Fig. 1. 50 × 50 GeV is a highly optimized lattice which is in turn based on the 1×1 TeV lattice [3], so there is a strong reason to assume the 750 × 750 GeV design shares most of the advantages with its “little brother”. IV. FINAL FOCUS SECTION The low beta function values at the IP are mainly pro- duced by three strong superconducting quadrupoles in the Final Focus Telescope with pole-tip fields of 9 T. Because of significant, large-angle backgrounds from muon decay, a background-sweep dipole is included in the final focus telescope and placed near the IP to protect the detector and the low-β quadrupoles [4]. Bend starts at 35 meters, so the FF system fits the Tevatron straight section footprint. P. Snopok (snopok@pa.msu.edu): Dept. of Physics and Astronomy, Biomedical Physical Sciences Building, East Lansing, MI 48824, USA; C. Johnstone (cjj@fnal.gov): MS 221 Fermilab, P.O.Box 500, Batavia IL 60510, USA Fig. 1. Baseline 50×50 GeV lattice scheme compared to the 750×750 lattice scheme V. CHROMATIC CORRECTION SECTION Local chromatic correction of the muon collider inter- action region is required to achieve broad momentum ac- ceptance. The CCS contains two pairs of sextupoles, one pair for each transverse plane, all located at locations with high dispersion. The sextupoles of each pair are located at positions of equal, high beta value in the plane (horizontal or vertical) whose chromaticity is to be corrected, and very low beta waist in the other plane. Moreover, the two sextupoles of each pair are separated by a betatron phase advance of near π, and each sextupole has a phase separation of (2n + 1) π 2 from the IP, where n is an integer. The result of this arrangement is that the geometric aberrations of each sextupole is canceled by its companion while the chromatic- ity corrections add. The sextupoles of each pair are centered about a minimum in the opposite plane (β min < 1), which provides chromatic correction with minimal cross correlation between the planes. A further advantage to locating the opposite planes minimum at the center of the sextupole, is that this point is π 2 away from, or “out of phase” with, the source of chromatic effects in the final focus quadrupoles; i.e. the plane not being chromatically corrected is treated like the IP in terms of phase to eliminate a second order chro- matic aberration generated by an “opposite-plane” sextupole. Repetitive symmetry and the fact that the transfer map of the section is unity implies that the important aberration (x|δδ) vanishes as well. The layout of the CCS is shown in Fig. 2. VI. ARC MODULE Flexible Momentum Compaction module (Fig. 3) provides negative momentum compaction values compensating for the positive momentum compaction generated by the Chro- maticity Correction Section. The small beta functions are