[en] Multifilamentary V₃Ga 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

[en] With an aim of developing new types of superconducting materials, Mo-N films and Mo/Si multi-layered films were fabricated by reactive and two-target sputtering methods, respectively. The superconducting properties such as T /SUB c/ , H /SUB c2/ and J /SUB c/ were examined. The crystal structure of Mo-N films changed from bcc to fcc with increasing N₂ gas flow rate during sputtering and a homogeneous fcc Mo₂N superconductor was obtained. On the other hand, the superconducting characteristics of the Mo/Si multi-layered film with a layer spacing 32.3 /SUP sf/ A were confirmed to be similar to those of amorphous Mo-Si alloys except the occurrence of anisotropic vortex pinning

[en] A superconducting material can be said to be characterized when sufficient of its properties have been measured for its response to be predicted under any conceivable experimental constraints. The experimental constraints constitute a moving target. The problems and pitfalls in making superconducting measurements on inhomogeneous superconducting materials are reviewed by reference to recent work on A15 and Nb-Ti conductors. The breadth of information available in comparative studies of inductive transitions and various types of resistive transition is assessed. The problem of the critical current criterion and its relation to a time dependent voltage-current characteristic is discussed as is the measurement and definition of the upper critical field in inhomogeneous superconductors

[en] Phonons emitted by superconducting tunneling junctions into insulator crystal substrates exhibit a sharp amplitude reduction above 85 GHz if the tunneling diodes are covered by ⁴He. This is attributed to the onset of an enhanced phonon transport into helium

[en] The energy gap spectra was observed for (TMTSF)₂ClO₄-Al₂O₃-Au junctions at 1.5 K by measuring their tunneling current characteristics. The superconducting gap was estimated to be less than 2 meV (Tsub(c) < 6K) which is much smaller than the previously reported value, 8 meV. (author)

[en] Wire breakage during fabrication of bronze process Nb₃Sn conductors has been linked to individual broken filaments within the wire. The wire breaks produce a cup and cone fracture with the tip of the cone centered on an enlarged filament rather than on the center of the wire. Samples of two different types of wire were sectioned longitudinally or cross-sectionally and examined for occurrence of irregular filaments. Enlarged and broken filaments were found and their occurrence analyzed. The enlarged heads of broken filaments are significantly harder than the matrix or the surrounding, undisturbed filaments. Broken filaments were found most frequently among filaments at the edges of filament groups near the center of the wire. Data on enlarged filament size distribution, hardness, and distribution within the wire are presented in the paper

[en] Loss measurement of superconducting cables are addressed, but only those of lengths from 1 m to 100 m. A method to measure short cables has been developed and is being improved. The method needed further improvement in order to make loss measurements of the BNL 138 kV, 4 kA, 100 m long superconducting cable now under construction. The cable system consists of two coaxial cables connected in a circular loop so that voltage and induced current can be applied simultaneously. During the ac loss measurements it will be run without high voltage. The short cable loss measurement and the 100 m cable system loss measurement circuits are illustrated. The new measurement method appears to be suitable for the BNL superconducting 100 m cable. In the case of a long cable the accuracy will be higher because of larger absolute losses, corresponding to a higher signal-to-noise ratio

[en] A computer program has been written to model thermal magnetic breakdown. It incorporates all the heat production and heat transport factors. The temperature of the defect and vicinity is calculated for increasing rf field levels until the defect grows unstably, determining the breakdown field level. Calculations are performed for a variety of circumstances to explore the relative influence of the various heat production and heat transport factors

[en] The objective of this investigation was to investigate systematically the two mechanisms of thermal transport in the cavity-cooling bath system: the thermal conductivity of the metal and heat transport across the metal to liquid helium interface. For this investigation, cavities were prepared with high thermal conductivity Nb; the thermal conductivity of this Nb at 4.2K was over 100 times higher than that of typical reactor grade Nb. To investigate the thermal transport processes, cavity surface temperature profiles were measured with dc heater power applied locally to the surface. The results agreed well with calculated equilibrium surface temperatures when reasonable values for the thermal boundary resistance between superconducting Nb and liquid He I or superfluid He II were used in the calculations. The microwave performance of the Nb cavities at X-band was considerably improved by the use of high thermal conductivity Nb; the high thermal conductivity Nb cavities consistently reached field levels over five times higher than the low thermal conductivity Nb cavities and sustained over 100 times as much dissipated power. These cavities never exhibited breakdown. Theoretical calculations showed that the performance of the low thermal conductivity Nb cavities was limited by the large temperature gradients at defects, whereas the performance of the high thermal conductivity Nb cavities was limited by transport of heat across the Nb liquid-He interface

[en] Experimental data have been obtained confirming the theoretical assumption of chaos existence in superconducting tunnel junctions (STJ) with hysteretic I-V curve (IVC) in the presence of the external microwave radiation for zero bias current. The dynamic of the chaos formation was investigated and the chaos intensity was estimated. Observation of chaotic oscillations for bias current smaller than the critical current are reported and discussed