Superconducting magnets used for plasma confinement in magnetic fusion energy systems operate at cryogenic temperatures. The support structures used to hold them in place act as a heat leak path from room temperature areas to the superconductors. This results in the need for additional cryogenic refrigeration capacity, which is expensive. High-strength, low thermal conductivity, radiation-tolerant materials are needed, particularly below the toroidal magnets where the gravity loads are greatest. Open-cell metallic foams can be made from high-strength, damage-tolerant, and radiation-tolerant materials such as tantalum or niobium. The high porosity of the foam (typically >80 vol%), combined with the tortuous path of the foam structure, results in very low thermal conductivity. Samples of structural open-cell foam will be made from various materials with various relative densities. The thermal conductivities and mechanical properties of the materials will be measured. Using those data, a low-conductivity support structure for the thermal isolation system will be fabricated. All cryogenic systems (not just those used in magnetic fusion confinement) are ultimately connected to a support that is at ambient temperature, and the structures along the connection path represent a heat leak path. By developing a structural insulator that is suitable for use with these systems, the material can be used in many different applications ranging from magnetic fusion confinement to particle accelerators for high-energy physics to superconducting power distribution systems to medical imaging machines.
