Development of long continuous Nb3Ge tape conductors with high current density at elevated temperature and field

Superconductors based on Nb3Ge have been fabricated by the chemical vapor deposition (CVD) process in continuous lengths up to 20 m. This material exhibits a transition temperature K and a self field critical current density A/cm²@ 14 K and offers the possibility of high current operation at temperatures > 14.0 K. Values of Jcmeasured in high magnetic fields exceed A/cm²at 18T @ 4 K. The material development program that resulted in reproducing the excellent short sample superconducting properties on long continuous lengths of tape is described. The tapes consist of 3-6 μm of Nb3Ge coated completely around 0.64-cm-wide, 25-μm-thick substrates of Cu, Ni, or Cu-clad stainless steel. More than 150 m of this tape has been fabricated for use in winding a 1-m prototype transmission cable. AC-loss measurements on short samples of the long tapes show complete shielding of the substrate and losses which are acceptably low for power transmission applications.