Position normalization is a method of manipulating data from any image source so that the effecti... more Position normalization is a method of manipulating data from any image source so that the effective information to noise ratio is dramatically increased. In this paper we present two very different examples of the application of position normalization used in the study of high current density superconductors. In the first example we use FESEM fractography to analyze grain boundary density and grain shape in micron-diameter filaments and then normalize the data obtained from individual grains to their positions with respect to the filament-matrix interface. In this way we extract the change of grain structure with position in apparently inhomogeneous microstructure. In the second example we analyze the backscattered electron intensity, BEI, from the cross-section of a superconductor filament with respect to its proximity to phase boundaries. In this way we extract small trends in the mean atomic number with a spatial resolution of better than 100 nm.
In this study, both pure and BaZrO3-doped superconducting YBCO films were fabricated on both sing... more In this study, both pure and BaZrO3-doped superconducting YBCO films were fabricated on both single crystal and buffered RABiTS substrates by a fluorine-free metal organic deposition (MOD) process. We succeeded in introducing nanoscale BaZrO3 (BZO) particles into YBCO films by adding extra Ba and Zr organic salts and were able to use multi-coating process to obtain high quality thick (up to ~ 1.1 μm) films. The pinning force density (Fp) in all BZO-doped YBCO samples is enhanced. The optimal BaZrO3 doping content investigated in this work is x = 0.10 for YBCO + x BZO films. Maximum pinning force density (Fp) exceeding 10 GN/m is obtained in ~ 200nm YBCO + 0.10 BZO film on SrTiO3 substrates and 5 GN/m in ~ 1.1μm YBCO + 0.10 BZO film on buffered RABiTS. The angular dependence of in-field critical current density (Jc) measurements shows Jc anisotropy is strongly reduced by BZO doping at 1 T and 4 T.
Magneto-optical imaging of the flux penetration into a Ag sheathed Bi1.8Pb0.4Sr2Ca2Cu3O8+x tape h... more Magneto-optical imaging of the flux penetration into a Ag sheathed Bi1.8Pb0.4Sr2Ca2Cu3O8+x tape has been used to extract the current flow paths in a magnetic field applied perpendicular to the c-axis. Using the large aspect ratio of the plate-like grain structure and the slab geometry of the sample to simplify the current-flow geometry, we converted the magneto-optical signal into two-dimensional (2D) field and current distributions. We found that the current patterns were very non-uniform and sensitive to weak magnetic fields of ∼ 400–800 Oe, even at 10 K. Current streamlines show that the effective current-carrying cross-section of the tape strongly depends on the field. Magnetization currents flow preferentially near the silver sheath, while the tape center supports mainly percolative and granular current patterns consisting of an array of macroscopic current loops whose long dimensions are of the order of the tape thickness. By comparing contour maps of the local Jc values with the microstructural images, we found that the high-Jc regions correlate with colonies of well-aligned long grains which are preferentially located near the silver interface, while the less aligned structure of smaller grains in the central part of the tape is associated with the granular behavior and much lower current-carrying capability. The wide distribution of the local Jc(x, y) revealed by magneto-optical imaging indicates that the performance of BSCCO-2223 tapes can be significantly improved if a larger fraction of well aligned grains can be produced more uniformly throughout the tape cross-section.
Fermilab has been steadily developing its SRF cavity expertise, infrastructure and technology bas... more Fermilab has been steadily developing its SRF cavity expertise, infrastructure and technology base. We particularly emphasize here recent developments in understanding basic material properties and developing a new chemistry treatment facility.
WITAMIR-I, a teandem mirror reactor, is a study by the University of Wisconsin fusion engineering... more WITAMIR-I, a teandem mirror reactor, is a study by the University of Wisconsin fusion engineering design group. Various engineering aspects and physics considerations are presented. WITAMIR-I is a high Q device with particularly attractive maintenance features and blanket characteristics.
Position normalization is a method of manipulating data from any image source so that the effecti... more Position normalization is a method of manipulating data from any image source so that the effective information to noise ratio is dramatically increased. In this paper we present two very different examples of the application of position normalization used in the study of high current density superconductors. In the first example we use FESEM fractography to analyze grain boundary density and grain shape in micron-diameter filaments and then normalize the data obtained from individual grains to their positions with respect to the filament-matrix interface. In this way we extract the change of grain structure with position in apparently inhomogeneous microstructure. In the second example we analyze the backscattered electron intensity, BEI, from the cross-section of a superconductor filament with respect to its proximity to phase boundaries. In this way we extract small trends in the mean atomic number with a spatial resolution of better than 100 nm.
In this study, both pure and BaZrO3-doped superconducting YBCO films were fabricated on both sing... more In this study, both pure and BaZrO3-doped superconducting YBCO films were fabricated on both single crystal and buffered RABiTS substrates by a fluorine-free metal organic deposition (MOD) process. We succeeded in introducing nanoscale BaZrO3 (BZO) particles into YBCO films by adding extra Ba and Zr organic salts and were able to use multi-coating process to obtain high quality thick (up to ~ 1.1 μm) films. The pinning force density (Fp) in all BZO-doped YBCO samples is enhanced. The optimal BaZrO3 doping content investigated in this work is x = 0.10 for YBCO + x BZO films. Maximum pinning force density (Fp) exceeding 10 GN/m is obtained in ~ 200nm YBCO + 0.10 BZO film on SrTiO3 substrates and 5 GN/m in ~ 1.1μm YBCO + 0.10 BZO film on buffered RABiTS. The angular dependence of in-field critical current density (Jc) measurements shows Jc anisotropy is strongly reduced by BZO doping at 1 T and 4 T.
Magneto-optical imaging of the flux penetration into a Ag sheathed Bi1.8Pb0.4Sr2Ca2Cu3O8+x tape h... more Magneto-optical imaging of the flux penetration into a Ag sheathed Bi1.8Pb0.4Sr2Ca2Cu3O8+x tape has been used to extract the current flow paths in a magnetic field applied perpendicular to the c-axis. Using the large aspect ratio of the plate-like grain structure and the slab geometry of the sample to simplify the current-flow geometry, we converted the magneto-optical signal into two-dimensional (2D) field and current distributions. We found that the current patterns were very non-uniform and sensitive to weak magnetic fields of ∼ 400–800 Oe, even at 10 K. Current streamlines show that the effective current-carrying cross-section of the tape strongly depends on the field. Magnetization currents flow preferentially near the silver sheath, while the tape center supports mainly percolative and granular current patterns consisting of an array of macroscopic current loops whose long dimensions are of the order of the tape thickness. By comparing contour maps of the local Jc values with the microstructural images, we found that the high-Jc regions correlate with colonies of well-aligned long grains which are preferentially located near the silver interface, while the less aligned structure of smaller grains in the central part of the tape is associated with the granular behavior and much lower current-carrying capability. The wide distribution of the local Jc(x, y) revealed by magneto-optical imaging indicates that the performance of BSCCO-2223 tapes can be significantly improved if a larger fraction of well aligned grains can be produced more uniformly throughout the tape cross-section.
Fermilab has been steadily developing its SRF cavity expertise, infrastructure and technology bas... more Fermilab has been steadily developing its SRF cavity expertise, infrastructure and technology base. We particularly emphasize here recent developments in understanding basic material properties and developing a new chemistry treatment facility.
WITAMIR-I, a teandem mirror reactor, is a study by the University of Wisconsin fusion engineering... more WITAMIR-I, a teandem mirror reactor, is a study by the University of Wisconsin fusion engineering design group. Various engineering aspects and physics considerations are presented. WITAMIR-I is a high Q device with particularly attractive maintenance features and blanket characteristics.
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Papers by D. Larbalestier