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[en] Qualitative pattern of thermal and hydrodynamic phenomena during the electrical explosion of thin metallic wires with clean and naturally contaminated surface is discussed. The results of experiments in compression of plasma resulted from the explosion of such wires in BIN high-current generator (250 kA, 400 kV, 100 ns) are compared and conclusion is made about coincidence of discharges through the contaminated wires and dielectrical filament. 10 refs.; 3 figs
[en] We study the effect of a fluctuating magnetic field, which is one of the technical problems for trapped magnetic fields in a bulk superconductor, to realize a practical bulk superconductor rotating machine. Previous research and other's research has shown that fluctuating magnetic fields reduce the strength of trapped magnetic fields in superconducting bulk modules [1, 2]. This deters development of applications of AC rotating machines because superconducting bulk modules are always exposed to a fluctuating magnetic field. Therefore, it is necessary to develop a method to control decrease of the trapped magnetic field. We propose a method to use the shielding ring of a superconducting wire to achieve this goal and the effects are confirmed experimentally . We are now building test equipment for examining the performance of a shielding ring in a bulk rotating machine. This paper reports the test result for the shielding ring applied to the bulk superconducting rotor that is a part of the test equipment.
[en] Due to the technological progress of the author's company over the last ten years we have succeeded in manufacturing long lengths of NbTi ultra fine filamentary wires for which the 50 Hz losses are greatly reduced. The conductors have many new prospective uses and this necessitates the reconsideration of the design of electrotechnical machines. One should take into account cryogenics and the very particular features of superconductors at the beginning of machine design. In this paper, the authors give the main features of the 50 Hz single-phase transformer constructed in their laboratory and the main cryogenic and electrical results that they have obtained, such as produced weight, limitation of fault current to a few percent of the rated current, room temperature efficiency better than 97% for active power of 70 kW
[en] Exploding wires are used in many high-energy applications, such as initiating explosives. Previous work analyzing gold wire burst in detonator applications has shown burst current and action metrics to be inconsistent with burst phenomenon across multiple firing-sets. Energy density better captures the correlation between different wire geometries, different electrical inputs, and explosive initiation. This idea has been expanded upon, to analyze the burst properties in power-energy space. Further inconsistencies in the understanding of wire burst and its relation to peak voltage have been found. An argument will be made for redefining the definition of burst. The result is a more broad understanding of rapid metal phase transition and the initiation of explosives in EBW applications.
[en] The linear stability of an array of a large number of thin wires is considered. The wires form a cylindrical surface, accelerated toward the axis under the action of a current. Stability equations are derived and a complete classification of the modes is presented. In agreement with Felber and Rostoker [Phys. Fluids 24, 1049 (1981)], it is shown that there exist two types of modes: medial modes, with deformation in the rz plane, and lateral modes, with only azimuthal deformation. For a given axial wave number, k, the most unstable medial mode has all the wires moving in phase similar to an axisymmetric mode for a continuous shell, whereas the most unstable lateral perturbation has opposite displacements of neighboring wires. Lateral modes are of particular interest because they may remain unstable for parameters where medial modes are stable. Numerical analysis of the dispersion relation for a broad range of modes is presented. Some limiting cases are discussed. It is shown that k1/2 scaling holds until surprisingly high wave numbers, even exceeding the inverse interwire distance. In the long-wavelength limit, the wires behave as a continuous shell with strong anisotropy of the electrical conductivity, i.e., high along the wires and vanishing across the wires. The results differ considerably from the modes of a thin, perfectly conducting shell. In particular, a new open-quotes zonal flowclose quotes mode is identified. copyright 1999 American Institute of Physics
[en] In this paper, issues related to the optimization of superconducting passive interconnects are discussed. Results of the microwave optimization of bends, via connections and crossings of superconducting microstrip lines (SMSLs) are reported. The optimum design of the SMSL cross gives more than 95% of transmission and can be well used in a two-bus cross design with up to 14 signal wires. The results have been confirmed by time-domain simulations and measurements
[en] Models of imploding wire arrays usually assume an expansion and instantaneous ionization of the array material with the subsequent implosion proceeding as a distinct array of individual plasma elements or as a cylindrical shell. Experimental evidence indicates that precursor plasmas form and implode ahead of the array, x-ray pulse lengths are longer than 1D models predict, and part of the array mass is left behind. Interferometry with 10 to 1 magnification is used to probe the initial plasma formation processes. Results on Al and C loads indicate that neutral Al vapor cores or solid C cores persist for up to 400 to 600 ns into the current pulse, and that precursor plasma formation is possible. These results predict similar behavior for the first 40 to 60 ns on current generators with I per wire ∼1.4 MA/μs
[en] A theoretical discussion is presented on the energy loss in a multifilamentary superconducting wire when an applied transport current and an external transverse magnetic field are varied simultaneously with a repeating pulsive wave form. In the present calculation, the effects of the 'uniforming time constant' is taken into account, together with the field dependence of the critical current density of superconducting filaments. The present analytic expression for the energy loss of multifilamentary wire is available to the whole range of the external magnetic field. It is shown that the contribution of the dynamic resistance loss to the total loss is strongly dependent on the position of the wire inside a coil. (author)
[en] The quantization of the magnetic fluxoid in the unit cells of a network of superconducting wires gives rise to a system with competing length scales determined by the resulting fluxoid lattice and the underlying network. This system provides an excellent experimental model for studying questions concerning the concept of commensurability, and the first emphasis of this thesis is on the formation of commensurate states in disordered and quasiperiodic geometries. Measurements of the resistive phase boundary Tc(H)|R reveal cusp-like structure signifying the existence of commensurate states at particular values of the applied field. The authors find that sufficient disorder in the tile areas will destroy all commensurate states in any network, and they accurately describe this behavior using the intuitive open-quotes J2 modelclose quotes in which one considers only the effects of supercurrents generated to satisfy fluxoid quantization (i.e., the London approximation). However, a disturbance of the local tile ordering destroys only certain types of commensurate states. They find that commensurability is not universally predicated by the presence of inflation symmetry in the lattice, but instead is more closely related to the Fourier transform of the lattice geometry. These experimental results in two dimensions are similar to analytical results for one-dimensional systems. Because the description of the superconducting networks using linearized Ginzburg-Landau theory is identical to a Schroedinger equation, these systems can be used to study the nature of electronic ground states on a two-dimensional lattice in a magnetic field. The second emphasis of this thesis addresses this problem in width-anisotropic square networks. They find that network anisotropy induces localization of the superconducting order parameter in one direction at incommensurate fields while in the perpendicular direction the order parameter remains extended