Electro-magnetic design and analysis of themagnetic system for the low energynuSTORM

The LEnuSTORM initiative at ESSnuSB requires a racetrack storage ring that can confine 600 MeV/cmuon beam with ±10% momentum spread while relying as far as possible on normal conductingmagnets. We opted for a dual approach in our design project: (i) an iron-dominated H-type dipoleaccelerator magnet, able to deliver the sought reference bending field, and (ii) a complete ring latticethat minimises particle loss for on- and off-momentum beams. Using CERN-ROXIE we optimised a 2-dimensional cross-section for a 400 mm-diameter aperturedipole. With 5 A/mm2 copper cables (10 008 A total) the magnet produces 1.516 T in the Good-FieldRegion while holding the integrated B-field error below the order of 10−3 over a 150–160 mm radius.The iron yoke saturation stays around 1.9 T, ensuring small head-room for current trimming withoutdisrupting its linear properties and thus degrading its quality. The ring optics were developed in MATLAB as well as in MAD-X. The main difficulty in designing thering optics with normal-conducting dipoles was suppressing the dispersion function efficiently. Hence,several designs have been considered and presented, each outperforming the others in various areas.The smallest beam size was obtained for the on-momentum design and had a maximum of 52.77 mmwhich accounts for 99.55% of the particles. To account for particles with moment deviation, a seconddesign is presented. This design is stable for particles with a moment deviation up to 6% but onlyaccount for 97.73% of particles when considering the beam size. Both of these design have a tightmagnetic configuration, leaving little room for sextupole correction at a later stage. Hence, a thirddesign is presented, using a DBA-cell the dispersion is suppressed at the end of the arc while containinglarger drift spaces between the magnets to accommodate sextupoles. However, this comes at the costof a larger beam size of 85.6 mm, which account for 92%. Each of the designs requires various amountsof super-conducting quadrupoles to maintain stable beam oscillations throughout the ring.