Richard D. Spal

Eddy‐current losses due to a surface crack in conducting material

Calculations are reported for the spatial distribution of magnetic fields in the neighborhood of a long surface crack in a conductor, where a uniform ac magnetic field is applied parallel to the length of the crack. The problem is resolved into tractable parts consisting of the cases of eddy currents near a semi‐infinite crack with a sharp tip and eddy currents near a square corner. The semi‐infinite crack problem is solved exactly by a modification of Sommerfeld’s diffraction theory and the corner problem is treated by a Green’s function obtained by the method of images. The composite solution is valid for a crack of depth equal to four times the electromagnetic skin depth or greater. From the solution, the Poynting vector is calculated and its integral over the surface computed. The change in power dissipation relative to the ’’uncracked’’ surface is given in a simple form.

NBS materials science beamlines at NSLS

Abstract Synchrotron radiation beamlines for topography, spectroscopy and small angle scattering at energies from 5 to 20 keV, are described.

Eddy currents in a conducting cylinder with a crack

We report calculations for the impedance of a long solenoid which surrounds a cylinder of conducting material containing a radial surface crack of constant depth. The calculation is accomplished by solving for the longitudinal ac magnetic field in the interior of the ’’cracked’’ cylinder in terms of an infinite series of cylindrical Bessel functions. All the coefficients in the series are determined in principle by boundary‐condtion requirements and the most significant terms are obtained numerically by truncation of the series. The resulting impedance is calculated for a wide range of values of the ratios of crack depth to radius and radius to skin depth. The results are tabulated in a form useful for nondestructive testing purposes.

Ultra-small-angle X-ray scattering to bridge the gap between visible light scattering and standard small-angle scattering cameras

Abstract This paper reports the performance of an ultra-small-angle X-ray scattering facility on beamline X23A3 at the National Synchrotron Light Source. Based on a Bonse-Hart double-crystal design, the instrument combines: continuously tunable optics with asymmetric first monochromator crystal, high-flux throughput, high-precision crystal rotators, independently-mounted reflecting crystals, photodiode detector and high-resolution X-ray video camera. This combination of features permits rapid small-angle X-ray scattering measurements in the scattering wave-vector range of 0.005–2.0 nm −1 (depending on the sample), with μm-positioning accuracy of a typical 3 × 3 mm 2 beam on the sample.

Structure of vapor-deposited yttria and zirconia thin films

Abstract The structures of thin films of zirconia and yttria, deposited by electron beam evaporation, have been examined by X-ray absorption fine structure (XAFS) analysis. It was found that the structure of the yttria film was similar to that of bulk yttria, which is a cubic oxide phase. The zirconia film, however, possessed a structure different from that of the bulk material. An analysis of the zirconia film data indicated a structure with a predominant tetragonal phase. Although lower coordination numbers were found in the films than in the standard powder specimens, it was not clear from the extended fine structure whether this deficit was due to film porosity observed in prior work or to the disorder that is generally observed in films. An analysis of the near-edge structure, however, suggested that porosity, rather than disorder, was present in the films. In addition, the K-edge positions observed for both the zirconia and the yttria films were higher in energy by approximately 3 eV than the corresponding K-edge in the powder specimens, indicating that the films may be more insulating than the standard bulk materials.

Hard X-Ray Microscope With Submicrometer Spatial Resolution

A high-resolution hard x-ray microscope is described. This system is capable of detecting line features as small as 0.6 µm in width, and resolving line pairs 1.2-µm wide and 1.2-µm apart. Three types of two-dimensional image detectors are discussed and compared for use with hard x rays in high resolution. Principles of x-ray image magnification are discussed based on x-ray optics and diffraction physics. Examples of applications are shown in microradiography with fiber reinforced composite materials (SiC in Ti3Al Nb) and in diffraction imaging (topography) with device patterns on a silicon single crystal. High-resolution tomography has now become a reality.

Production of uniform field gradients for magnetometers by means of current‐carrying strips

Current‐carrying strips are a convenient means to produce a uniform field gradient for use in a Faraday magnetometer. An expression is derived for the magnetic field gradient, taking into account the images of the strips in the pole pieces. Tables are presented giving the magnitude and homogeneity of the gradient for various strip widths and locations. The performance in the laboratory of a set of strips is reported.

An X-ray monochromator crystal which detects the bragg condition

Abstract We have fabricated a (111) silicon X-ray monochromator crystal with a diode diffused into its surface. Without suffering any apparent degradation in its or rocking-curve width at the Bragg condition, the crystal provides a dc current which changes dramatically at the diffraction of a monochromatic X-ray beam. The current change is directly attributable to extinction at the Bragg angle. It provides a new means to align the two crystals of a double-crystal X-ray monochromator using a feedback circuit.

High resolution synchrotron X-radiation diffraction imaging of crystals grown in microgravity and closely related terrestrial crystals

Irregularities in three crystals grown in space and in four terrestrial crystals grown under otherwise comparable conditions have been observed in high resolution diffraction imaging. The images provide important new clues to the nature and origins of irregularities in each crystal. For two of the materials, mercuric iodide and lead tin telluride, more than one phase (an array of non diffracting inclusions) was observed in terrestrial samples; but the formation of these multiple phases appears to have been suppressed in directly comparable crystals grown in microgravity. The terrestrial seed crystal of triglycine sulfate displayed an unexpected layered structure, which propagated during directly comparable space growth. Terrestrial Bridgman regrowth of gallium arsenide revealed a mesoscopic structure substantially different from that of the original Czochralski material. A directly comparable crystal is to be grown shortly in space.

Supercurrent dissipation and strain-induced damage in (Bi, Pb)2Sr2Ca2Cu3O10/Ag tape

Supercurrent dissipation and strain-induced damage in (Bi, Pb)2Sr2Ca2Cu3O10/Ag high-temperature superconductor composite tape, at 77 K in self-field, are studied by I–V curve analysis. Five dissipation models are considered, and differently processed tapes are compared. After making self-field corrections, which are normally ignored but we find essential to do, collective flux creep stands out as the only dissipation mechanism which explains the data. Confidence in the analysis comes not only from the goodness of fit, but also from experimental confirmation of two fitted parameters. The identification of the main dissipation mechanism has great practical value, because it enables definitive tape characterization, based on intrinsic physical properties.