An innovative superconducting magnetic cage concept for compact plasma with high NWL: design and analysis

This paper presents the electromagnetic and structural assessment of the magnetic cage for the Volumetric Neutron Source (VNS), featuring 12 Toroidal Field Coils (TFC), 6 Poloidal Field Coils (PFC), and a Central Solenoid (CS). The set of analyses presented here aims to validate this architecture at a pre-conceptual design level. A key aspect of this design is the placement of the PFCs inside the toroidal chamber, in contrast to ITER external PFCs configuration. This arrangement significantly reduces the required poloidal current, enhancing plasma control while introducing structural and manufacturing challenges. The toroidal field coil system has been designed using the MADE algorithm, defining a consistent winding pack (WP) layout and conductor arrangement. A novel in-situ winding strategy is proposed to address assembly constraints. The TF coil structure assumes HTS tapes or react-and-wind Nb3Sn strands, with 316LN stainless steel selected as the casing material based on mechanical and thermal performance criteria. The electromagnetic analysis, based on a numerical model in ANSYS APDL, evaluates the magnetic field distribution and Lorentz forces acting on the coil system. Structural assessments, including stress and deformation analysis, confirm that the TF casing can withstand operational loads, with equivalent stresses remaining within allowable limits except for minor localized regions. The study also considers cooldown effects and dead weight loads, ensuring structural integrity across different operational phases.