S. Pourrahimi

Improved high field performance of Nb-Al powder metallurgy processed superconducting wires

Improved overall critical current densities Jc’s were achieved with powder metallurgy processed Nb‐A1 which combined reduced powder sizes and increased nominal areal reductions R. Increased Jc values were obtained for a variety of different heat treatments. For a Nb‐8 wt. % A1 wire with R=3.4×105 a very short treatment at 1100 °C followed by a 750 °C treatment gave (at 4.2 K)Jc>104 A/cm2 at 19 T; a 900 °C treatment followed by a 750 °C treatment gave Jc=104 A/cm2 at 18 T and, at 2 K, Jc was greater than 104 A/cm2 at 20 T; and a treatment of 800 °C for 8 h gave (at 4.2 K)Jc=104 A/cm2 at 17.5 T.

Nb-Al powder metallurgy processed multifilamentary wire

Powder metallurgy processed Nb-Al wire with overall critical current densities, J c , at 4.2K up to 104A/cm2at 19T has been investigated in more detail, Kramer plots and directly measured H c2 values of samples with different heat treatments show an increase in H c2 at 4.2K up to 24.5T. Test coils, using long lengths of wire, and tested in fields up to 15T, show J c values equal to those of short samples. Multiple strand hydrostatic small scale extrusions were made. A number of third element additions including B, Mg, Co, Cr and Ni in fine powder form were incorporated in the P/M processing but these did not improve J c . ac losses were measured and used to determine J c at 10w fields. The high field ac losses are lower than that for any In Situ or powder processed Nb 3 Sn wires.

Nb/sub 3/Al wire produced by powder metallurgy and rapid quenching from high temperatures

Powder-metallurgy-processed Nb-25-at.% Al wires were annealed at temperatures just below the melting temperature. Depending on anneal conditions, the entire Nb-Al part of the wire could be rapidly quenched as a metastable Al Nb(Al) solid solution with an Al concentration exceeding 23 at.%. This A2 phase is sufficiently ductile to be bent without incurring damage. A second anneal at 950 degrees C converted the A2 into A15. J/sub c/ was 10/sup 4/ A/cm/sup 2/ at 22 T, and T/sub c/ was 17.8 K. The rapid quenching of Nb-Al powder metallurgy processed wire is a possible alternative to obtain improved high-field properties. >

600 MHz spectrometer magnet

An NMR-grade superconducting magnet has been constructed which operates in persistent mode at 14.25 T at reduced temperature. The stored energy is 840 kJ. The magnet incorporates niobium-titanium and niobium-tin multifilamentary conductors. In the persistent mode all windings are in series with superconducting joints between sections. Six of the joints are hybrids, niobium-tin joined to niobium-titanium. The niobium-titanium windings reached short sample without training. The niobium-tin sections suffered two training quenches before reaching 14.25 T. >

Scaleup of powder metallurgy processed Nb-Al multifilamentary wire

Powder metallurgy processed Nb-Al superconductIng wires were fabricated from billets up to 45 mm o.d. with nominal areal reduction ratios, R, up to 2 × 105, Nb powder sizes from 40 to 300 μm from various sources, Al powder sizes from 9 to 75 μm, Al concentrations from 3 to 25 wt % Al and with a wide range of heat treatments. All the compacts used tap density powder in a Cu tube and swaging and/or rod rolling and subsequent wire drawing. Both single strand and bundled wires were made. Overall critical current densities, J c , of 2 × 104A/cm2at 14 T and 104A/cm2at 16 T were achieved for 6 to 8 wt % Al in Nb.

Thermal and Hydraulic Measurement in the ITER QUELL Experiments

The Japan Atomic Energy Research Institute has a collaboration with the European Union, the United States of America and the Russian Federation for the International Thermonuclear Experimental Reactor (ITER). In the engineering design activity for ITER, a test coil named QUench Experiments on Long Length (QUELL), using 91 m and 1/5-size ITER superconducting conductor, was fabricated by JAERI. The performance tests were carried out at the SULTAN facility in Switzerland where quench propagation, thermal and hydraulic characteristics were determined and development and test of new quench detection system were conducted. The thermal and hydraulic behavior was not known well. This conductor has a central channel to reduce the pressure drop. In order to investigate the thermal and hydraulic characteristic of the conductor, the pressure drop has been measured at 5–13 K and 2–11 g/s, and the friction factor of the central channel was calculated. In heat slug propagation, an inductive and resistive heater on the conductor has been used and the velocity of the heat front and input energy are estimated from the temperature change of conductor.

Conductors for a 1 GHz superconducting magnet

The development of a high resolution high-field 1 GHz NMR spectrometer has been undertaken by Battelle Pacific Northwest Laboratories (BPNL). In preparation for the design of the superconducting magnet for that instrument, BPNL sponsored a program to measure the properties at high field (up to 23.5 T) and low temperature (1.8 K) of a number of commercially available superconductors. Lengths of these conductors were obtained and tested as short samples and in small coils. The critical current densities, index values and strain dependence of these properties were characterized. The potential applications of these conductors in construction of a 1 GHz NMR magnet are discussed. >

21 Tesla powder metallurgy processed Nb 3 Sn(Ti) using (Nb-1.2 wt%Ti) powders

Powder metallurgy (P/M) processed Nb 3 Sn(Ti) wires were made with alloyed Nb(Nb-1.2wt%Ti) powders using a Cu-45wt% (Nb-1.2wt%Ti) composite. Nominal areal reductions of about 104were used and Sn was introduced by means of a central Sn core. With a Sn-5wt%Cu core a critical current density J c = 104A/cm2at 4.2K was measured at 19.7 tesla. Further additions of Ti were made using Sn-xwt%Ti cores furnished by M. Suenaga of Brookhaven National Laboratory. Values of J c (4.2K) = 104A/cm2at 21.4 tesla were achieved. These values are larger than those obtained with Cu-45wt%Nb P/M processed wires. The effects of prestrain are compared with unalloyed Nb P/M processing. Higher values of J c are obtained in strain-free wires and/or at temperatures below 4.2 K. Electron microprobe measurements of the Ti distribution throughout the single core wires are also presented.

Powder metallurgy processed Nb 3 Sn employing extrusion and varying Nb content

Extension of powder metallurgy (P/M) processing of Cu-Nb-Sn is described for small scale industrial uniaxial extrusion ( R \leq 10^{4} ) and for small scale hydrostatic extrusions for areal reductions R = 2000. Successful 2.5 cm o.d. uniaxial P/M processed extrusions at 950 and 250°F were obtained. Model cold hydrostatic extrusions of single tin core and multitin core wire are described. The effect of Nb content for Cu-x wt% Nb, where 36 \leq \times \leq 60 was examined. Increased over-all critical current densities, J c were obtained with increased Nb content up to 50 wt% Nb. For proper comparisons, values of J cm (where the prestress is removed), are given for several compositions. Improvement in J c for T \leq 4.2 K is also presented. Incorporation of Tl in Nb 3 Sn by means of Sn-Ti core processing results in further increases in J c . The low R and large initial powder sizes result in relatively thick Nb fibers which are not completely reacted. The present extrusion P/M processed wires demonstrate several practical approaches for development of high performance materials. Optimization should yield high values of J c at 20 tesla.

Submicron filament multistrand powder metallurgy processed Cu-Nb-Sn wire

Submicron size ultrafine Cu-Nb-Sn superconducting wire has been fabricated by the powder metallurgy process simulating large scale industrial fabrication using the bundling technique. Starting copper and niobium powders ranged from 250 to 500 μm. Both external and tin core processed wires were fabricated with overall current densities of J_{c} \sim 2-3 \times 10^{4} A/cm2at 14 T, demonstrating that both particle size and billet can be scaled up to large scale fabrication.