The design and construction of a computer-compatible system to measure and record optical retardation with a polarizing or interference microscope

The design, construction and operation of a computer-compatible system to measure and record optical retardation with a polarizing or interference microscope is described. The system consists of a high precision potentiometer linked directly to the drum vernier of a compensator or analyser. A highly stabilized fixed voltage is applied to the potentiometer and the voltage difference between the potentiometer wiper and one end of the resistance element is directly proportional to the compensator or analyser angle. This voltage is converted to a digital format, interfaced with a digital time base and stored on punched paper tape for subsequent computer analysis.     

Epitaxial Solution Deposition of YBa2Cu3O7−δ-Coated Conductors

A variety of solution deposition routes have been reported for processing complex perovskite-based materials such as ferroelectric oxides and conductive electrode oxides, due to ease of incorporating multiple elements, control of chemical stoichiometry, and feasibility for large area deposition. Here, we report an extension of these methods toward long length, epitaxial film solution deposition routes to enable biaxially oriented YBa₂Cu₃O_7−δ (YBCO)-coated conductors for superconducting transmission wires. Recent results are presented detailing an all-solution deposition approach to YBCO-coated conductors with critical current densities J _c (77 K)>1 MA/cm² on rolling-assisted, biaxially textured, (200)-oriented Ni–W alloy tapes. Solution-deposition methods such as this approach and those of other research groups appear to have promise to compete with vapor phase methods for superconductor electrical properties, with potential advantages for large area deposition and low cost/kA·m of wire.     

Pancake Vortices

I describe the magnetic-field and current-density distributions generated by two-dimensional (2D) pancake vortices in infinite, semi-infinite, and finite-thickness stacks of Josephson-decoupled superconducting layers. Arrays of such vortices have been used to model the magnetic structure in highly anisotropic layered cuprate high-temperature superconductors. I show how the electromagnetic forces between pancake vortices can be calculatated, and I briefly discuss the effects of interlayer Josephson coupling.     

Flux-line-cutting threshold in type II superconductors

The threshold for flux-line cutting (intersection and cross-joining of adjacent nonparallel vortices) is considered theoretically for a model array of parallel, equally spaced vortex planes. The vortices within each plane are parallel to each other but are inclined at an angle with respect to vortices in adjacent planes. Forces between vortices are calculated numerically using the interaction force proposed by Brandt, Clem, and Walmsley. Although for small interplanar angles the array is stable, for sufficiently large angles infinitesimal perturbations of the array grow until flux-line cutting occurs.This work was supported by the U.S. Department of Energy, contract No. W-7405-Eng-82, Division of Materials Sciences, budget code AK-01-02-02-3.     

The energy spectrum of cosmic-ray induced neutrons measured on an airplane over a wide range of altitude and latitude

Crews of high-altitude aircraft are exposed to radiation from galactic cosmic rays (GCRs). To help determine such exposures, the Atmospheric Ionizing Radiation Project, an international collaboration of 15 laboratories, made simultaneous radiation measurements with 14 instruments on a NASA ER-2 high-altitude airplane. The primary instrument was a sensitive extended-energy multisphere neutron spectrometer. Its detector responses were calculated for energies up to 100 GeV using the radiation transport code MCNPX 2.5.d with improved nuclear models and including the effects of the airplane structure. New calculations of GCR-induced particle spectra in the atmosphere were used to correct for spectrometer counts produced by protons, pions and light nuclear ions. Neutron spectra were unfolded from the corrected measured count rates using the deconvolution code MAXED 3.1. The results for the measured cosmic-ray neutron spectrum (thermal to >10 GeV), total neutron fluence rate, and neutron dose equivalent and effective dose rates, and their dependence on altitude and geomagnetic cut-off agree well with results from recent calculations of GCR-induced neutron spectra.     

Investigations of electric dipole fields in type II superconductors during flux flow

Electric dipole fields in the mixed state of rectangular superconducting foils are investigated both theoretically and experimentally. These fields are generated by imposing an ac current to a contact pair during steady flux flow driven by a transport current and are measured using a second, movable contact pair. Theory predicts that the electric dipole field can be described by an anisotropic flux flow conductivity, whose components _x and _y are related by _x / _y =1–(j _c /j) cos² , where j is the dc current density, j _c is the dynamic critical current density, and is the field angle. Except for low j values at the threshold of flux flow, good agreement with experiment is found.This work was supported in part by U.S. Department of Energy, Contract No. W-7405-Eng-82, Division of Materials Sciences, budget code AG-01-02-03-3.