Numerical Investigation of Cooling Performance of Liquid Hydrogen and Helium for a 20 K HTS Toroidal-Field Coil

High-temperature superconducting (HTS) magnets for compact fusion systems operate typically at 8-20 K. Liquid hydrogen is a feasible coolant within this temperature range, offering favorable thermophysical properties and economic advantages. In this study, a 20 K operating point is considered, where liquid hydrogen is a candidate coolant. Baseline heat loads of a SPARC-scale toroidal-field (TF) coil are estimated. A coupled 3D solid heat-transfer and 1D pipe-flow model is used to compare helium and liquid hydrogen cooling with an inlet temperature of 20 K and an outlet pressure of 10 bar. Charging and pulse-operation stages are considered. Under a common temperature-rise constraint (ΔT ≤ 1 K), the minimum mass flow rate is determined. One-factor sensitivities of the peak magnet temperature and channel pressure drop are quantified. Lower minimum mass flow rates, lower peak magnet temperatures, and smaller channel pressure drops are predicted for liquid hydrogen within the stated assumptions. These results suggest that liquid hydrogen can be a viable coolant option for 20 K-class TF coils under the stated assumptions, while further design, safety assessment, and validation are needed.