In a superconducting system, the primary current leads establish a bridge between ambient and cryogenic environments. The leads conduct both electrical and thermal energy between the two terminations. Thermal and electrical losses across these conductors represents a significant efficiency penalty to the overall system. Optimization of current leads using conventional materials such as copper makes use of the Weidman Franz Approximation. This approximation stipulates that for a given material, the ratio of thermal to electrical conductivity is proportional to temperature and the Lorentz number, and is therefore independent of material^[1]. Published research suggests that heterogeneous or anisotropic materials such as stochastic metal foam or pressed graphite may deviate from the Weidman Franz Approximation and thus offer an improved ratio of electrical to thermal conductivity^[2].

The present research provides experimental results for conventional conductors, stochastic foam, and pressed graphite as potential cryogenic current leads. Electrical conductivity was measured across a range of temperatures between ambient and 77K. Thermal conductivity was measured using the one-imensional fin equation across a representative sample. The results provide both an insight into potential material advances for current leads, and an experimental basis for testing advanced materials such as nanotubes or printed materials with unique structures. The results also highlight the challenge in accurately measuring key physical properties across cryogenic and transition temperatures. The majority of cryogenic literature takes the Weidman Franz Approximation as a given, but it will be shown that significant deviations are possible when measured experimentally.