An iron core circuit to balance the current of insulated strands in superconducting cables

Cables of insulated strands reduces ac losses in superconducting magnets even at frequencies below 1 Hz. Their current imbalances, however, make the magnet unstable, and this problem has been discussed for the last 15 years. I have proposed to insulate the normal strands of the current leads to each other and to connect them individually to the superconducting strands of the magnet. The currents of the strands in this design are balanced well by the electrical resistance present in the current leads. This is, however, not effective at high frequencies which require high resistance. In order to balance the current of strands carrying dc and ac of higher, including commercial frequencies, I propose to pass two insulated strands through an iron core and to send currents through them in opposite directions. This current balancer has as many iron cores as there are strands. Even in a very large magnet, where the inductance variation of individual insulated strands circuits is of the order of 10 /spl mu/H and the current is about 100 A, strand currents would be balanced well with iron cores of only a few centimeters in size.