Preparation and critical currents of vapour-deposited Nb3Sn compound

Conclusion The presented results have shown that by optimizing some of the basic technological parameters of the chemical vapour-deposition process it is possible to increase substantially the critical currentI _c and the Nb₃Sn layer thickness of the produced superconductor without any other technological treatment.The critical currentI _c reported byEnstrom et al. 7] concerning the pure reaction atmosphere without doping gases, is about 13 A/mm (per 1 mm of the tape width), in our case it is 62 A/mm in transverse magnetic field of 5 T. We have shown that as far as the Nb₃Sn tape length of the order of 100 m is concerned, it seems more advantageous to work with Nb/Sn chlorides ratio for the region of 0·55 to 0·87 in contrast to the value of 0·33 reported byEnstrom et al. 7]. As we have already mentioned, further increase of theI _c andJ _c values may be achieved by means of doping gases injection into the reaction atmosphere or by additional heat treatment 11] etc.As it is also reported byEnstrom et al. 7], by doping the gaseous ambient with 0·1% CO₂, the increase ofI _c from 13 A/mm to 84 A/mm in the magnetic field of 5 T may be obtained. As the preliminary results of our investigation have shown, an increase from 32 A/mm to 106 A/mm by using the doping gases may be achieved for the tape travelling velocity of 4 m/h, the Nb/Sn chlorides ratio equal to 0·55 and the substrate heating current of the value of 4 A.We expect that by optimizing the technological parameters mentioned above together with following doping and additional heat treatment, we may obtain a substantial increase in theI _c andJ _c values.