Hiroshi Tateishi

Fiber-reinforced-superconductors for a 15 T-class high-field pulsed magnet and their conceptual design

The authors are developing a novel type of Nb/sub 3/Sn superconductor with high elastic modulus fibers for application to high field pulsed superconducting magnets, called the fiber-reinforced superconductor (FRS). They describe the conceptual design of a conductor for a pulsed magnet using FRSs and present superconducting characteristics for monofilamentary FRS samples. Each monofilamentary FRS supports hoop stress under operation of the magnet. Short lengths of monofilamentary FRSs using tungsten fiber were prepared by RF-magnetron sputtering. Critical current measurement up to 15 T and a uniaxial strain test at 10 T have been carried out. The data support the conceptual design of the 15-T-class pulsed superconducting magnet using FRSs.<<ETX>>

Mechanical properties of a niobium-tin superconductor reinforced by tantalum cores

We have been developing fiber-reinforced type of niobium-tin superconductor for large scale high field magnets. In this conductor, each niobium-tin filament has a tantalum core. Tantalum is selected as material for the core since it has good ductility with mechanical strength and hence a conventional drawing method can be applied to fabricate a conductor. Stress-strain characteristics and the irreversible strain limits of the conductor with different heat-treatment conditions are measured. Combining these results, discussions about the mechanical properties of the conductor are presented.

Properties of fiber-reinforced niobium-tin superconductor fabricated by bronze process

We are developing a fiber reinforced type of superconductor for large scale, high-field magnets. Formerly we used the sputtering process to develop a niobium-tin conductor reinforced with a tungsten fiber and showed that this type of conductor has excellent stress tolerance. For practical applications however, a conventional fabrication process like bronze process is desirable. Hence we have tried to fabricate a fiber-reinforced type niobium-tin conductor utilizing tantalum fiber as the reinforcing member, In this conductor, each niobium-tin filament has a tantalum core of about 20-/spl mu/m diameter, We adopted tantalum as the core material since it has both good ductility and mechanical strength comparable to stainless steel, This conductor showed a reasonable critical field of about 22 T and good mechanical strength compared to a niobium-tin conductor fabricated by the conventional bronze process.

Influence of Ta-reinforcement geometry in Nb/sub 3/Sn wires

We have been developing tantalum-fiber-reinforced bronze process niobium-tin wires for use in large-scale high field magnets. They are fabricated by conventional drawing. We manufactured two kinds of the wires with different geometries but similar volume ratios. We have investigated their characteristics and have clarified that there are some differences in their superconducting critical current, critical magnetic field, critical temperature, and the influence of their heat-treatment conditions.

Properties of multifilamentary Nb/sub 3/Sn fiber-reinforced superconductors for high field pulsed magnets

We are developing Nb/sub 3/Sn fiber-reinforced superconductors (FRS) for high field pulsed magnets. Multifilamentary FRS are fabricated by sputtering niobium and bronze around 22 tungsten fibers of 20-/spl mu/m diameter. The conductors are then heat-treated in an electric furnace and are solder-filled after plating copper chemically. Critical current densities of FRS have been measured up to 14.5 T. We have investigated the effect of heat-treatment conditions, tin concentration of bronze and titanium addition into niobium. Tensile stress-strain measurement showed that FRS has excellent stress toughness.<<ETX>>

DC and pulse operations of 4 MJ pulsed superconducting magnet and its stress analysis

4 MJ pulsed magnet was tested in dc and pulse operating modes, It was successfully charged up to 5940 A ( 4.6 MJ, 6.9 T) at 0.15 T/sec and discharged at 3.5 T/sec without quenching. Strains due to hoop stress were measured and analysed using a spring model. It is pointed out that they do not necessarily propagate from turn to turn and hence the strains measured at the outer support band may be small. A residual compressive force in the magnet windings was also analysed. Ac losses were measured using a 3 MJ pulsed magnet having almost the same structure and conductor as 4 MJ magnet and shown to be fairly small.

AC losses of NbTi superconducting wires with fine filament

An investigation was conducted of the AC losses in coils with NbTi superconducting wires. The authors used the multiple-stacking procedure to prepare the wires, which varied in filament size from 10 mu m to 0.07 mu m. Three kinds of wires with 0.07- mu m filament were specially fabricated to estimate the proximity effect on AC losses. The distances between the filaments of these wires were 21 nm, 42 nm, and 70 nm, respectively. AC losses were measured for small coils at 60 Hz. The proximity effect was observed for the wires with 0.07- mu m filament when the distance was 21 nm. Conversely, when the distance was 42 nm, the loss decreased to the small value of 11 kW/m/sup 3/ at 0.5 T and 4.2 K. >

NbTi Superconducting Wires for AC Use

NbTi superconducting wires with very fine filaments were developed for AC use. Critical current density shows a large value of 1×104 (A/mm2) in a low magnetic field when the filament size is 0.07 µm. Upper critical field decreases from 11 Tesla for 0.6 µm and reaches 9 Tesla for 0.03 µm. 5 KVA coils using these wires were successfully operated under alternating currents.

Energy transfer experiments between 3 MJ and 4 MJ pulsed superconducting magnets

The pulsed power supply system for a 3 MJ pulsed superconducting magnets by using an energy storage magnet and a transfer circuit was constructed. It is composed of both 3 MJ and 4 MJ pulsed superconducting magnets (named PSM-3 and SMES-4, respectively) and the energy transfer apparatus which consists of the chopper circuit with a capacity of about 5000 kW. The reversible energy transfer experiments between SMES-4 and PSM-3 were carried out, and with the SMES-4 charged up to 4.24 MJ initial energy, the PSM-3 was successfully charged up to 2.45 MJ (4950 A, B m : 5.94 T) in 1.5 seconds and also up to 2.9 MJ (5400 A, B m : 6.48 T) in 3.0 seconds. The maximum delivery power was about 3270 kW. The energy transfer efficiency in one way transfer was about 93 %, and the current ripple was less than 0.01% of a rating current. The two pulsed magnets showed very stable performances during the energy transfers.

Titanium or tantalum additions to Nb/sub 3/Sn layers from reinforcement fibers in fiber-reinforced-superconductors

Fiber-reinforced-superconductors (FRS) of Nb/sub 3/Sn were prepared using titanium and tantalum fibers. Their superconducting characteristics were estimated by separating the effects of prestrain from them. The results have shown that the tantalum fiber functions both as a reinforcement for FRS and as a source that supplies tantalum elements to improve the high-field properties of Nb/sub 3/Sn. The characteristics were degraded inversely when a titanium fiber was used. In the case of preparing a FRS using a titanium-added niobium target, the characteristics improved. The discrepancy in global pinning force between monofilamentary FRS and multifilamentary FRS is also shown.<<ETX>>