Method of fabricating superconductive electrical conductor

A method of fabricating a superconductive electrical conductor of Nb.sub.3 Sn type comprising the steps of:

• covering an elongated core member made of Nb with a covering member consisting of a third element for improvement of a critical current of Nb.sub.3 Sn contained in the superconductive electrical conductor;
• covering said elongated core member covered with said covering member with a first tubular matrix made of any one of a Cu-Sn alloy and a combination of Cu with Sn to form a first composite wire element;
• reducing said first composite wire element to a predetermined diameter to form a second composite wire element;
• assembling a predetermined number of said second composite wire elements in a second tubular matrix made of any one of a Cu-Sn alloy, Cu and a combination of Cu with Sn to form a third composite wire element;
• reducing said third composite wire element to a predetermined diameter to form a fourth composite wire element;
• assembling a predetermined number of said fourth composite wire elements in a third tubular matrix made of any one of a Cu-Sn alloy, Cu and a combination of Cu with Sn, and subsequently reducing said third tubular matrix having therein said fourth composite wire elements to a predetermined diameter to form a multi-core composite wire;
• and
• subjecting said multi-core composite wire to a diffusion heat-treatment to form an intermetallic compound of Nb.sub.3 Sn and said third element in a peripheral portion of said Nb core member.