In a system of thin alternating layers of superconductors and insulators the equations describing static and dynamic fluxon solutions are derived. The approach, represented by a useful compact matrix form, is intended to describe systems fabricated for example of niobium or niobium-nitride thin films; in the limit of ultrathin superconductor films it may give a model for describing fluxon motion in layered high-T, superconductors. Numerical examples of current versus voltage curves to be expected in such an experiment are presented.

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A 5× increase of the critical current density (Jc) at 77 K was obtained by coating a coevaporated 500 nm thick Y, BaF2, Cu film with 50 nm Ag prior to the ex situ annealing. Jc increased from 0.2 for uncoated samples to 1 MA/cm2 for the Ag-coated sample without severely affecting the zero resistance transition temperature (Tc0). Scanning electron microscopy showed that the surface morphology was improved and that the normally observed trellislike structure was greatly reduced. By combining electron microscopy and sputter assisted Auger analysis it was found that the Ag nucleated in droplets on the surface of the superconductor with only small amounts of Ag in the superconductor matrix. X-ray diffraction confirmed that the Ag-coated film was highly c-axis oriented. The increase in Jc is believed to be due to the improved surface properties of the superconductor, indicating that a larger amount of the film is c-axis oriented or that the single-crystalline grains are larger.

The propagation of a plane electromagnetic wave through a Lorentz plasma in a sheared magnetic field is considered. The characteristic waves in a uniformly sheared, but otherwise homogeneous, medium are found, and their properties presented graphically. Some effects introduced by the presence of shear are investigated by means of elementary applications of the uniform-shear theory. By suggested extensions of the analysis, refinements may be made in the interpretation of microwave diagnostic experiments with controlled-fusion containment devices having complicated sheared fields. . I N T R O D U C T I O NA COMMON refinement to the Appleton-Hartree theory of electromagnetic wave propagation in a magnetized (anisotropic) plasma is consideration of spatial inhomogeneity of the plasma electron density (BACHYNSKI, 1960). In this paper, we investigate another type of inhomogeneity, namely, spatial variation of the orientation of the magnetic field. The problem is suggested by the importance of sheared magnetic fields in the plasma containment devices of controlled fusion research, such as the diffuse pinch, the multipolar Stellarator, and the Ioffe stabilized mirror configuration.Initially assuming a simple model for the sheared field, we derive a dielectric tensor and the resulting wave equations. Then with further simplifying assumptions, we find the characteristic waves in a 'uniform' sheared medium. The general problem, for an arbitrarily complicated model of magnetic field configuration and electron density profile, may be set u p by a straightforward extension of the analysis given. 5617

Long length Bi-2223/Ag tapes with high critical current densities are needed for large-scale applications. In this paper, recent results from NST are being presented, describing recent results reaching critical current densities of 23 kAlcm2 and engineering critical current densities of 5.2 kAlcm2 at 77 K over the whole length of a 1250 metre long Bi-2223/Ag tape. To our knowledge this is the highest critical current density reported for Bi-2223/Ag tapes longer than 1 km. The approach for improving the homogeneity and the considerations of processing and handling the long length tape are presented. Various Ag alloy sheathed Bi-2223 tapes have been made by our standard production line. The properties of these tapes are compared.