Comparative Study of Epoxy-Wollastonite Composites and Sn55PbAgSb Solder for Helium Cooling Channels in Toroidal Field Coil Casings

Abstract

To address the thermal management challenges under extreme operational conditions of tokamak toroidal field (TF) magnets, this study systematically compared the cryogenic performance of epoxy-wollastonite composites (EWC) implemented in ITER and Sn₅₅PbAgSb solder (SPAS) applied in EAST for helium cooling channels, based on the Comprehensive Research Facility for Fusion Technology (CRAFT) TF coil casing. Through finite element heat transfer modeling at 4.2 K with heat flux ranging from 1 W/m²to 30 W/m², the results demonstrate that cooling channels fabricated with SPAS solder exhibit a 2.12–5.32% reduction in the average cold-side temperature (T_cs) compared to EWC, with the performance gap narrowing to 0.23% at ultra-low heat flux conditions (1 W/m²). The mechanical testing under 77 K cryogenic conditions demonstrates superior crush resistance in EWC (no defects at 400 kN) compared to solder-based counterparts (crack initiation observed at 200 kN). The findings establish a material selection protocol: SPAS is optimal for high heat flux regions to enhance thermal dissipation, while EWC is preferred in mechanically critical zones to ensure structural integrity. These results offer actionable engineering guidelines, balancing thermal efficiency and mechanical robustness for future fusion reactors.