S. Meguro

Technical and Cost Evaluation on SMES for Electric Power Compensation

RASMES (Research Association of Superconducting Magnetic Energy Storage) in Japan developed a road map of SMES for fluctuating electric power compensation of renewable energy systems. Based on the progress of large superconducting coils, the technical status is already established to develop the several MWh class SMES for frequency control, load fluctuation compensation, and generation fluctuation compensation. With integrated operations of several dispersed SMES systems, it is expected that the 100 MWh class SMES for load fluctuation leveling (peak cut) can be introduced in the period of 2020-30, and the first 1 GWh class SMES for daily load leveling can be installed in the period of 2030-40. From the results of Japanese national projects, experimental device developments and SMES design studies, if the output power of SMES is 100 MW, the target cost of SMES can be evaluated with 2000 USD/kW of the unit cost per output power (the unit cost per kW).

Development towards ultra-thin superconducting solenoid magnets for high energy particle detectors

Abstract Development towards ultra-thin superconducting solenoid magnets for high energy particle detector has been carried out by focusing on aluminum stabilized superconductor mechanically reinforced while keeping electrical resistivity as low as possible. It has been realized by using combined technologies of “micro-alloying” and “cold-work hardening”. Further general efforts to realize transparent solenoids are also discussed.

Development of high-strength and high-RRR aluminum-stabilized superconductor for the ATLAS thin solenoid

The ATLAS central solenoid magnet is being constructed to provide a magnetic field of 2 Tesla in the central tracking part of the ATLAS detector at the LHC. Since the solenoid coil is placed in front of the liquid-argon electromagnetic calorimeter, the solenoid coil must be as thin (and transparent) as possible. The high-strength and high-RRR aluminum-stabilized superconductor is a key technology for the solenoid to be thinnest while keeping its stability. This has been developed with an alloy of 0.1 wt% nickel addition to 5N pure aluminum and with the subsequent mechanical cold working of 21% in area reduction. A yield strength of 110 MPa at 4.2 K has been realized keeping a residual resistivity ratio (RRR) of 590, after a heat treatment corresponding to coil curing at 130/spl deg/C for 15 hrs. This paper describes the optimization of the fabrication process and characteristics of the developed conductor.

High-strength and high-RRR Al-Ni alloy for aluminum-stabilized superconductor

The precipitation type aluminum alloys have excellent performance as the increasing rate in electric resistivity with additives in the precipitation state is considerably low, compared to that of the aluminum alloy with additives in the solid-solution state. It is possible to enhance the mechanical strength without remarkable degradation in residual resistivity ratio (RRR) by increasing content of selected additive elements. Nickel is the suitable additive element because it has very low solubility in aluminum and low increasing rate in electric resistivity, and furthermore, nickel and aluminum form intermetallic compounds which effectively resist the motion of dislocations. First, Al-0.1wt%Ni alloy was developed for the ATLAS thin superconducting solenoid. This alloy achieved high yield strength of 79 MPa (R.T.) and 117 MPa (4.2 K) with high RRR of 490 after cold working of 21% in area reduction. These highly balanced properties could not be achieved with previously developed solid-solution aluminum alloys. In order to achieve higher strength than the above, Al-Ni alloys of up to 2.0 wt% Ni content were investigated. Al-2.0wt%Ni alloy achieved yield strength of 120 MPa (R.T.) and 167 MPa (4.2 K) with RRR of 170 after cold working of 20% in area reduction.

Very high critical current density of bronze-processed (Nb,Ti)/sub 3/Sn superconducting wire

From the viewpoint of fabricability, the Sn content in the bronze matrix of bronze-processed Nb/sub 3/Sn wire is limited to below 15 wt%. This limitation results in a higher matrix-to-niobium ratio of bronze-processed Nb/sub 3/Sn wire than other high-Sn-content wires, such as the tube-processed Nb/sub 3/Sn wire. This is a reason why the non-Cu critical current density (J/sub C/) of the bronze-processed Nb/sub 3/Sn wire is lower than that of tube-processed Nb/sub 3/Sn wire. Therefore, increasing the Sn content in the bronze matrix and reducing the bronze ratio is the key to enhancing the non-Cu J/sub C/ of the bronze-processed Nb/sub 3/Sn wire. A bronze-processed Nb/sub 3/Sn superconducting wire with a Cu-16wt%Sn-0.2wt%Ti matrix was successfully fabricated on a production scale. The wire achieved a high non-Cu J/sub C/ of approximately 1000 A/mm/sup 2/ at 12 T and 4.2 K.

Enhancement of Critical Current Densities by the Prebending Strain at Room Temperature for Nb3Sn Wires

The influence of a repeated bending strain at room temperature on the critical current densitiy of bronze route Nb3Sn wires was investigated. We found that the critical current Ic is significantly increased by applying a repeated bending load (pre-bending treatment) at room temperature. The maximum enhancement of Ic was approximately twice at 16 T for CuNb-reinforced Nb3Sn wires by a 0.5% prebending strain and the critical current density Jc became about 528 A/mm2 at 4.2 K and 16 T. A comparison of the stress dependent Ic values obtained before and after applying prebending treatments for CuNb/Nb3Sn wires indicates that not only the stress dependence of Ic but also the maximum Ic at the axial strain-free state are improved. The improvement of the stress dependent Ic is in agreement with the prediction made based on the calculation using the uniaxial stress/strain distribution model. Moreover, the increase in the maximum Ic may be related to the release of stress/strain states along the radial direction through prebending treatments.

(Nb,Ti)/sub 3/Sn superconducting wire with CuNb reinforcing stabilizer

An in-situ CuNb composite shows a high strength and a high electrical conductivity. Therefore, it is a suitable material for the reinforcement of Nb/sub 3/Sn superconducting wire. Many studies about mechanical and electrical properties of Nb/sub 3/Sn wire with CuNb reinforcing stabilizer have been carried out, but a fabricability of the long-length wire was not confirmed. In this study, 1 mm-diameter (Nb,Ti)/sub 3/Sn superconducting wire with Cu-20 wt%Nb reinforcing stabilizer was fabricated 22 km in length. The wire showed a good fabricability throughout the production. Mechanical properties and critical currents are evaluated in comparison with un-reinforced one.

(Nb,Ti)/sub 3/Sn superconducting wire reinforced with Nb-Ti-Cu compound

Reinforcement of Nb/sub 3/Sn wires is required for high field superconducting magnets because the Nb/sub 3/Sn superconductor is very sensitive to mechanical strain and its critical current degrades drastically at a higher absolute strain than 0.3%. Recently, Nb/sub 3/Sn superconducting wires reinforced with tantalum, Cu-Nb alloy and Al/sub 2/O/sub 3/-dispersed copper, have been developed. But, these high-strength wires do not show very high strength at an absolute strain of 0.3% because these reinforcements have a similar Youngs modulus to copper. In addition, Nb/sub 3/Sn layers of these wires experience an additional compressive strain caused by the differences in thermal contraction between reinforcements and Nb/sub 3/Sn layers. Such a compressive strain also decreases the critical current of the wire. An intermetallic compound was selected as a reinforcement for Nb/sub 3/Sn superconducting wire because such a compound is expected to have a high Youngs modulus and a similar thermal contraction to the Nb/sub 3/Sn compound. Fortunately, the Nb-Ti-Cu compound can be formed from the Nb-Ti and copper composite during reaction heat treatment for Nb/sub 3/Sn layers. Therefore, (Nb,Ti)/sub 3/Sn superconducting wire reinforced with the Nb-Ti-Cu compound has been fabricated. The wire shows a 0.2% proof stress of 400 MPa and maintains a critical current density equal to the unreinforced wire.

Development of high-strength Nb/sub 3/Sn conductor

Nb/sub 3/Sn superconducting wires reinforced with Cu-Ni/Nb-Ti composite have been developed. Nb/sub 3/Sn wires reinforced with Cu-Ni/Nb-Ti showed good mechanical and electrical properties. In this study, 1.2 mm-diameter (Nb, Ti)/sub 3/Sn superconducting wire of 13 km in length reinforced with Cu-Ni/Nb-Ti was successfully fabricated. Moreover, the effect of copper fraction to the strength of the wire was studied.

Large T/sub c/, B/sub c2/ and I/sub c/ enhancement effect due to the prebending treatment for bronze route Nb/sub 3/Sn wires

In order to develop a react-and-wind (R&W) processed Nb/sub 3/Sn superconducting magnet, we investigated the influence on the superconducting properties due to the prebending treatment. Since a reacted Nb/sub 3/Sn superconducting wire reveals a very sensitive response from stress and strain, we focus on the prebending treatment which is repeatedly applied to the Nb/sub 3/Sn wire through several pulleys in the R&W coil winding process. We found that the prebending treatment doubles the I/sub c/ value at 20 T and 4.2 K for bronze route Nb/sub 3/Sn wires. This I/sub c/ enhancement effect comes from the T/sub c/ and B/sub c2/ enhancement. It turned out that T/sub c/ increases from 17.4 to 17.9 K and as a result B/sub c2/ also increases from 23.7 to 25.2 T at 4.5 K for bronze route multifilamentary Nb/sub 3/Sn wires prebent at bending strain of 1.0% and at 5 repeated times.