Critical current densities in Nb3Ge between 14 and 21 K

Self field critical current densities of thick Nb3Ge films have been measured in the liquid hydrogen temperature range 13.8 - 21 K. Bulk critical current densities Jcabove 1.6 × 10⁶A/cm²were observed at 14 K falling linearly at higher temperatures. The behavior extrapolated to zero critical current gave a critical temperature Tc∼ 19.2 K which is ∼1.5 K lower than the onset Tcdetermined from the a.c. magnetic susceptibility. The samples were long sections of copper tubes, which had been coated on the inside with Nb3Ge by a chemical vapor deposition process. Jcfor various high Tcmaterials are compared including calculations of adiabatic stability. Nb3Ge holds promise for a dc superconducting power transmission line operating near 14 K.