A conductor assembly for transmitting power includes a former that defines a shape, a superconductor material disposed around the former, and a thermally insulating jacket (TIJ) disposed around and spaced apart from the superconductor material. An outer surface of the superconductor material and an inner surface of the TIJ can define an annulus through which a coolant can flow. The conductor assembly can also include an external layer, disposed around an outside surface of the TIJ, to provide structural support to the conductor assembly. The conductor assembly can also include an electrical insulation layer disposed around the outside surface of the TIJ or around the superconductor material.

The sheath (3) is a material, which includes an aluminium (Al) matrix, in which nanometric aluminium oxide particles (Al.sub.2O.sub.3) are homogenously dispersed, the content of Al.sub.2O.sub.3 is 0.25 to 5 vol. % and the balance is Al. It is preferred that Al.sub.2O.sub.3 originates from the surface layer present on Al powder used as feedstock material for consolidation. The superconductor based on magnesium diboride (MgB.sub.2) core (1) is fabricated by powder-in-tube or internal magnesium diffusion to boron technology, while the tube is the Al+Al.sub.2O.sub.3 composite, which is a product of powder metallurgy. A loose Al powder is pressed by cold isostatic pressing, and then the powder billet is degassed at elevated temperature and under vacuum, and then is hot extruded into a tube. A thin diffusion barrier (2) tube filled up with a mixture of Mg and B powders or Mg wire surrounded with B powder is placed into the Al+Al.sub.2O.sub.3 composite tube under inert gas or vacuum. Such composite unit is cold worked into a thin wire and then annealed at 625-655° C. for 8-90 min, what results in a formation superconducting MgB.sub.2 in a wire's core (1).

The sheath (3) is a material, which includes an aluminium (Al) matrix, in which nanometric aluminium oxide particles (Al.sub.2O.sub.3) are homogenously dispersed, the content of Al.sub.2O.sub.3 is 0.25 to 5 vol. % and the balance is Al. It is preferred that Al.sub.2O.sub.3 originates from the surface layer present on Al powder used as feedstock material for consolidation. The superconductor based on magnesium diboride (MgB.sub.2) core (1) is fabricated by powder-in-tube or internal magnesium diffusion to boron technology, while the tube is the Al+Al.sub.2O.sub.3 composite, which is a product of powder metallurgy. A loose Al powder is pressed by cold isostatic pressing, and then the powder billet is degassed at elevated temperature and under vacuum, and then is hot extruded into a tube. A thin diffusion barrier (2) tube filled up with a mixture of Mg and B powders or Mg wire surrounded with B powder is placed into the Al+Al.sub.2O.sub.3 composite tube under inert gas or vacuum. Such composite unit is cold worked into a thin wire and then annealed at 625-655° C. for 8-90 min, what results in a formation superconducting MgB.sub.2 in a wire's core (1).

A persistent current switch includes a superconducting wire, a heater, and an insulating member. The superconducting wire includes a substrate and a superconducting layer provided on the substrate. The superconducting layer includes a first principal surface facing the substrate and a second principal surface on an opposite side of the first principal surface. The heater is disposed only on the second principal surface side with respect to the superconducting layer. The insulating member is provided between the second principal surface of the superconducting layer and the heater.

A persistent current switch includes a superconducting wire, a heater, and an insulating member. The superconducting wire includes a substrate and a superconducting layer provided on the substrate. The superconducting layer includes a first principal surface facing the substrate and a second principal surface on an opposite side of the first principal surface. The heater is disposed only on the second principal surface side with respect to the superconducting layer. The insulating member is provided between the second principal surface of the superconducting layer and the heater.

A superconducting device includes a superconducting cable having a plurality of superconducting tapes in a plurality of phases, including a first phase, and at least one further phase. One or more superconducting tapes of the first phase is in electrical contact with one or more superconducting tapes of the at least one further phase through at least one resistive barrier that prevents current from passing between the first phase and the at least one further phase in the absence of a voltage between one or more of the superconducting tapes of the first phase or the at least one further phase. The first phase is electrically connected in series to at least one further phase.

A superconducting device includes a superconducting cable having a plurality of superconducting tapes in a plurality of phases, including a first phase, and at least one further phase. One or more superconducting tapes of the first phase is in electrical contact with one or more superconducting tapes of the at least one further phase through at least one resistive barrier that prevents current from passing between the first phase and the at least one further phase in the absence of a voltage between one or more of the superconducting tapes of the first phase or the at least one further phase. The first phase is electrically connected in series to at least one further phase.

An oxide superconductor according to an embodiment includes an oxide superconducting layer includes a single crystal having a continuous perovskite structure containing at least one rare earth element selected from the group consisting of yttrium, lanthanum, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium, barium, and copper, containing praseodymium in a part of the site of the rare earth element in the perovskite structure, and having a molar ratio of praseodymium of 0.00000001 or more and 0.2 or less with respect to the sum of the at least one rare earth element and praseodymium; fluorine in an amount of 2.0×10.sup.15 atoms/cc or more and 5.0×10.sup.19 atoms/cc or less; and carbon in an amount of 1.0×10.sup.17 atoms/cc or more and 5.0×10.sup.20 atoms/cc or less.

An oxide superconductor according to an embodiment includes an oxide superconducting layer includes a single crystal having a continuous perovskite structure containing at least one rare earth element selected from the group consisting of yttrium, lanthanum, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium, barium, and copper, containing praseodymium in a part of the site of the rare earth element in the perovskite structure, and having a molar ratio of praseodymium of 0.00000001 or more and 0.2 or less with respect to the sum of the at least one rare earth element and praseodymium; fluorine in an amount of 2.0×10.sup.15 atoms/cc or more and 5.0×10.sup.19 atoms/cc or less; and carbon in an amount of 1.0×10.sup.17 atoms/cc or more and 5.0×10.sup.20 atoms/cc or less.

A superconducting power cable system, including: a superconducting power cable including a cryostat, a first cooling station, a second cooling station, wherein the superconducting power cable extends between the first cooling station and the second cooling station, wherein the first cooling station is configured to pump cooling fluid into the cryostat in a first direction towards the second cooling station and the second cooling station is configured to pump cooling fluid into the cryostat in a second direction, opposite to the first direction, towards the first cooling station, an access pipe assembly arranged between the first cooling station and the second cooling station, the access pipe assembly extending into the cryostat for tapping cooling fluid flowing from the first cooling station and the second cooling station from the cryostat, and a return pipe structure arranged externally to the superconducting power cable, the return pipe structure connecting the access pipe assembly to the first cooling station and to the second cooling station, and providing a respective return cooling fluid line from the cryostat through the access pipe assembly to the first cooling station and to the second cooling station.