The SOLEIL II upgrade relies on a lattice combining 7BA and 4BA High-Order Achromat (HOA) cells. Strict compact- ness constraints and energy efficiency objectives have driven the adoption of permanent magnet based technology for the main bending and focusing elements, while quadrupole correctors, sextupoles, and octupoles remain resistive to pre- serve operational flexibility. This paper presents the latest progress in the design, optimization, and prototyping of the SOLEIL II magnet system.

The SOLEIL II sextupoles are equipped with additional windings to provide normal and skew dipole corrections. Accurate modeling of these combined-function sextupole magnets are particularly challenging due to magnetic saturation, hysteresis, and internal cross-talk between channels. Based on 3D magnetic simulations, polynomial, interpolation-based, and neural-network models were developed to reproduce the saturation and cross-talk effects. These nonlinear models were validated on the first prototype magnet, providing preliminary confirmation of their reliability and demonstrating the feasibility of implementing sextupole-corrector magnets in the SOLEIL II storage ring.