D.G. Howe

Multifilamentary V 3 Ga wire: A critical review

Initial studies of V 3 Ga conductors formed by the bronze technique coincided with early work on Nb 3 Sn conductors; however, due to several technological difficulties, emphasis to date has been on commercial production of Nb 3 Sn composites. The superior critical current density of V 3 Ga in high magnetic fields (H> 10T), however, favor this conductor in selected applications. Improvements in critical current density have been achieved by using a modified bronze technique whereby the filaments as well as the Cu matrix are alloyed with Ga. Recent studies of the temperature and magnetic field dependence of the critical current density as well as stress effects, and third element additions are presented. Superconducting applications which may benefit from the use of V 3 Ga wire will be emphasized.

Improved critical current capability of V3Ga formed in a V-6Ga/Cu-15 Ga composite

Single filament V/sub 3/Ga composite wires were prepared by imbedding cores of pure V and V--6.1 at.% Ga in a Cu--15.4 at.% Ga matrix. The parabolic growth rate of V/sub 3/Ga was enhanced by alloying the core, and the superconducting critical current density was nearly doubled. At 4.2 K J/sub c/ exceeded 10/sup 5/ A/cm/sup 2/ in transverse magnetic fields up to 140 kG. (auth)

Processing and properties of superconducting V3Ga composites

A processing technique to form V3Ga in composite wires of V and a Cu‐15.4 at. % Ga alloy is outlined. The structure sensitivity of the superconducting properties of V3Ga are demonstrated through quenching curve data. Improved Jc(H) properties are obtained with decreasing reaction temperatures, superconducting layer thickness, and wire core diameter.

Critical current properties of multifilament V 3 Ga wire at temperatures above 4.2 Kelvin

Studies of the superconducting properties of V 3 Ga formed in composite wires by solid state reaction are presented. Multifilament wires were fabricated containing nineteen V-6.1 at.%Ga filaments or thirty V-8.0 at. %Ga filaments in a Cu-17.5 at .%Ga matrix. A study of J c as a function of magnetic field and temperature on these wires is reported. At a temperature of 8.6 K, and in a magnetic field of 10 Tesla, a J c of 4.2 × 105amps/ cm2was measured for the thirty filament wire. This is significantly higher than the J c of commercially available V 3 Ga tape Or Nb 3 Sn wire, These studies indicate that not only does our V 3 Ga wire exhibit high magnetic field properties Superior to those for commercially available wire at 4.2 K, but it also retains its superior J c values at temperatures in excess of 11 K.

Stress effect on I/sub c/ of multifilamentary V/sub 3/Ga wire

Measurement of stress effects on the critical current Ic of multifilament V3Ga wire are reported, and the cryostat for performing these studies is described. Measurements were taken at 4.2 K in a magnetic field of 9.0 T and for stress values up to 5×108 Pa. Noticeable degradation of Ic did not begin in the wires reported here until stress values of 3.0×108 Pa. The first effect of stress was to produce a measurable resistance in the wire below Ic. A discussion of this low‐current onset of resistance is given which suggests that improved stress characteristics in A15 wires may correlate with the reduction or elimination of this resistance.

Stress effect on Ic of multifilamentary V3Ga wire

Measurement of stress effects on the critical current Ic of multifilament V3Ga wire are reported, and the cryostat for performing these studies is described. Measurements were taken at 4.2 K in a magnetic field of 9.0 T and for stress values up to 5×108 Pa. Noticeable degradation of Ic did not begin in the wires reported here until stress values of 3.0×108 Pa. The first effect of stress was to produce a measurable resistance in the wire below Ic. A discussion of this low‐current onset of resistance is given which suggests that improved stress characteristics in A15 wires may correlate with the reduction or elimination of this resistance.

Pulsed magnetic field losses and critical current densities of V3 Ga and Nb3Sn multifilament superconductors

Abstract Pulsed magnetic field loss measurements have been performed on special V3Ga filament superconductors, which are known to have very high critical current densities, and on a NB3Sn filament superconductor. The dependence of the hysteresis losses on the diffusion heat treatment parameters for the V3Ga layer formation is reported. To analyse the results, the hysteresis losses of hollow superconducting filaments in parallel and perpendicular magnetic fields were calculated. From E.J. Kramers theory of flux pinning we postulate that, for a given material, upper and lower intrinsic limits of the hysteresis losses are due to the flux line shearing effect. A part of the results was presented at the ICEC 7.

Critical current properties of V3Ga with third element additions

Abstract Critical current densities of over 1.7 × 10 6 Acm −2 at 10T and 4.2K have been achieved in multifilamentary V 3 Ga wire produced by a modified bronze technique. Attempts to further improve this value were made by adding a third element, either Ti or Zr, to the V-Ga alloy filaments along with Al to the Cu-Ga matrix. The effects of reaction temperature and layer thickness with the third element additions were qualitatively similar to those measured for wires without third element additions, ie lower reaction temperatures and smaller layer thickness gave higher J c values. At low reaction temperatures, these composite wires with third element additions exhibited slower growth rates and lower J c values than those obtained for V-Ga cores in a Cu-Ga matrix, at higher temperatures just the opposite was true. In all cases, however, the J c values obtained were lower than the best we have been able to achieve using V + Ga filaments and Cu + Ga matrix under optimum conditions.

Recent developments on processing and properties of V 3 Ga composite wires

The addition of small amounts of third elements to V-Ga alloy rods have resulted in improvements in ductility. Cerium, yttrium, and titanium additions have been studied. Cerium (0.2atomic%)and yttrium (0.2 atomic%) additions reduced the microhardness from 180 to 160 KG/mm2. Lower mlcrohardnesses in alloy rods facilitates the metallurgical processing to small filament diameters used in multifilamentacy V 3 Ga wire. The effects of these alloy additions on V 3 Ga wire formed by the modified bronze technique are presented. Progress is reported on the development of high critical current density V 3 Ga wires using the V-Ga/Cu-Ga modified bronze process.

Metallurgical and superconducting properties of multifilamentary V 3 Ga wires

Multifilamentary V 3 Ga wires containing small additions of yttrium have been produced commercially for the Naval Research Laboratory by Airco Superconductors Inc. These conductors containing 55 and 3025 filaments were metallurgically processed through a combination of hot extrusion and wire drawing. The yttrium additions were found to soften the vanadium alloy and consequently enhance the size reductions necessary to produce the wire without detrimental effects to previously achieved growth rates and critical current properties.