Nb Wires Research Articles

Microstructure of seal formed between a Nb wire and an Al2O3 capillary melted by YAG laser radiation

Abstract Cracks occasionally develop inside the glass frit, the sealing material used in ceramic metal-halide lamps that employ polycrystalline alumina as the arc-tube material, although the rate at which these cracks develop is low. Therefore, we proposed a new method to stop their development. Our method did not make use of a glass frit and involved the formation of a seal between the Nb wire and the Al 2 O 3 capillary melted by the radiant energy from a YAG laser. However, cracks or voids developed inside the melted Al 2 O 3 capillary. Therefore, in order to control the Al 2 O 3 microstructure inside the melted Al 2 O 3 capillary and thus to obtain a better seal, grain growth was suppressed by combining the processes of annealing after melting and grain-boundary deposition of Ta. The Al 2 O 3 microstructure could be controlled by these factors. Thus, optimized conditions for forming the seal were achieved.

Influence of crystallization inside glass frit on seal stress in ceramic metal halide lamps

Ceramic metal halide lamps use polycrystalline aluminum oxide as an arc tube material; cracks inside the glass frit—used as the seal material—have been known to occur occasionally. This study measured the stress on the lamp seals caused by changes in the cooling rate during the sealing process by a 2D stress measurement method. Seal stress decreased with reducing cooling rate. Therefore, we discuss the influences of the glass frit's microstructure and the coefficients of thermal expansion (glass frit, capillary, and Nb wire) on the seal stress. The coefficient of thermal expansion of the annealed glass frit was essentially closer to those of the capillary and Nb wire, while that of the rapidly cooled glass frit differed greatly. Moreover, the glass frit of the rapidly cooled lamp seal contained only an amorphous phase (Dy, Si, Al, and O), while the glass frit of the annealed lamp seal contained both an amorphous phase (Dy, Si, Al, and O) and a crystalline one (Dy2SiO5 and Al2O3). Fracture toughness was found to be larger in the crystals than in the amorphous phase area. Moreover, it was larger in the area where crystalline Dy2SiO5 and Al2O3 were present compared to the area where only crystalline Dy2SiO5 was present.Thus, the coefficient of thermal expansion of the glass frit containing the crystalline phase was found to influence the seal stress. Furthermore, the crystallization in the glass frit was found to influence crack propagation. Therefore, formation of cracks inside the glass frit can be prevented by optimizing these factors, which can be achieved by changing the cooling rate in the sealing process without changing the specifications of the glass frit (composition, composition ratio, etc.).

Transport measurements on nano-engineered two dimensional superconducting wire networks

Superconducting triangular Nb wire networks with high normal-state resistance are fabricated by using a negative tone hydrogen silsesquioxane (HSQ) resist. Robust magnetoresistance oscillations are observed up to high magnetic fields and maintained at low temperatures, due to the effective reduction of wire dimensions. Well-defined dips appear at integral and rational values (1/2,3/8,1/4) of the reduced flux f=Φ/Φ0. These results are consistent with theoretical calculations for the reduced critical temperature as a function of f.

Localization of superconductivity in superconductor–electromagnet hybrids

We investigate the nucleation of superconductivity in a superconducting Al strip under the influence of the magnetic field generated by a current-carrying Nb wire, perpendicularly oriented and located underneath the strip. The inhomogeneous magnetic field, induced by the Nb wire, produces a spatial modulation of the critical temperature Tc, leading to a controllable localization of the superconducting order parameter (OP) wavefunction. We demonstrate that close to the phase boundary Tc(Bext) the localized OP solution can be displaced reversibly by either applying an external perpendicular magnetic field Bext or by changing the amplitude of the inhomogeneous field.

Development and Prospects for the Future of Superconducting Wires

Superconducting wires are important from the viewpoints of energy saving and the realization of a low-carbon society, because their applications in various types of electric power applications enable not only improved efficiency but also the reduction of size and weight owing to the fact that they can allow a large electric current density without resistance. Wires of Nb–Ti and Nb3Sn metallic superconductors have conventionally been used in various magnets. The research and development of high-temperature Cu-oxide superconducting wires has been intensively carried out focusing on Bi- and Y-based oxides; recently, the development of long wires of these oxides has also been in progress, and their applications to a variety of power systems are being eagerly discussed. MgB2, whose superconductivity was discovered in Japan in 2001, is also being studied with the aim of fabricating MgB2 wires, and promising performance has been obtained. The research and development of superconducting wires using these materials is expected to achieve further progress and lead to their practical applications in the future.

Niobium Wires as Space Holder and Sintering Aid for Porous NiTi

AbstractWhen NiTi powder compacts containing Nb wires are heated above 1 170 °C, each Nb wire reacts with adjacent NiTi powders to form a eutectic liquid which wicks into the space between the remaining NiTi powders. This creates a macropore at the location of the Nb wire while eliminating the microporosity between NiTi powders which is filled with a NiTi/Nb eutectic phase after solidification. This novel method produces – in a single step and without applied pressure – a dense NiTi matrix with elongated pores suitable for shape memory or superelastic applications such as bone implants, dampeners and actuators.

Diffusion Stop-Layers for Superconducting Integrated Circuits and Qubits With Nb-Based Josephson Junctions

New technology for superconductor integrated circuits has been developed and is presented. It employs diffusion stop-layers (DSLs) to protect Josephson junctions (JJs) from interlayer migration of impurities, improve JJ critical current (I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> ) targeting and reproducibility, eliminate aging, and eliminate pattern-dependent effects in I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> and tunneling characteristics of Nb/Al/AlO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> /Nb junctions in integrated circuits. The latter effects were recently found in Nb-based JJs integrated into multi layered digital circuits. E.g., it was found that Josephson critical current density (J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> ) may depend on the JJ's environment, on the type and size of metal layers making contact to niobium base (BE) and counter electrodes (CE) of the junction, and also change with time. Such J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> variations within a circuit reduce circuit performance and yield, and restrict integration scale. This variability of JJs is explained as caused by hydrogen contamination of Nb layers during wafer processing, which changes the height and structural properties of AlO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> tunnel barrier. Redistribution of hydrogen impurities between JJ electrodes and other circuit layers by diffusion along Nb wires and through contacts between layers causes long-term drift of J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> . At least two DSLs are required to completely protect JJs from impurity diffusion effects-right below the junction BE and right above the junction CE. The simplest and the most technologically convenient DSLs we have found are thin (from ~3 nm to ~10 nm) layers of Al. They were deposited in-situ under the BE layer, thus forming an Al/Nb/Al/AlO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> /Nb penta-layer, and under the first wiring layer to junctions' CE, thus forming an Al/Nb wiring bi-layer. A significant improvement of J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> uniformity on 150-mm wafer has also been obtained along with large improvements in J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> targeting and run-to-run reproducibility.

Análise da resistência ao desgaste de revestimento duro aplicado por soldagem em facas picadoras de cana-de-açúcar

O setor sucroalcooleiro brasileiro tem apresentado um expressivo crescimento nos últimos anos, entretanto, a manutenção das indústrias apresenta um elevado custo devido à perda de metal dos equipamentos por mecanismos de desgaste. O objetivo deste trabalho é estudar a aplicação de revestimentos duros por soldagem com arames tubulares quanto à resistência ao desgaste de facas picadoras de cana-de-açúcar, comparando os resultados obtidos em laboratórios com os aplicados em campos. Foram utilizados quatro tipos de consumíveis utilizados na indústria sucroalcooleira: um eletrodo revestido da liga FeCrC de 4,0 mm de diâmetro e três arames tubulares autoprotegidos de 1,6 mm de diâmetro, de ligas Fe-23,1Cr-4,11C, Fe-22Cr-4,5C-6,5Nb, Fe-1,8C-7,5Cr-1,5Mo-5,26Ti. O metal de base utilizado foi um aço SAE 1020. Foram construídos corpos de prova para a avaliação de desgaste em laboratório com abrasômetro Roda de Borracha segundo a norma ASTM G65-91. Posteriormente, foram construídas facas picadoras de cana-de-açúcar, revestidas com as mesmas condições de soldagem e montadas no picador de uma destilaria de álcool. A avaliação de desgaste foi feita via perda de massa. As soldagens com os arames tubulares foram efetuadas no modo de transferência por curto-circuito, com mesmos valores de corrente e tensão de soldagem. O arame contendo Nb apresentou a maior resistência ao desgaste em laboratório e devido à presença de trincas e ao lascamento do revestimento, a menor resistência ao desgaste em campo. O arame FeCrC e o arame contendo Ti e Mo apresentaram resistência ao desgaste similar, com o pior desempenho em laboratório e o melhor em campo. Comparados ao eletrodo revestido, apenas o arame contendo Nb apresentou similar desempenho em laboratório e o arame FeCrC e o arame com adição de Ti e Mo, similar desempenho em campo.

Nonlocal injection of spin current into a superconducting Nb wire

Pure spin current injection into a superconductive Nb was demonstrated experimentally by employing a nonlocal spin absorption technique in a multiterminal lateral structure. From the reduction in spin signals, we found the absorption efficiency remained almost unchanged even after superconducting transition. The Nb/Cu interface properties were also complementarily examined by using a Nb/Cu/Nb junction incorporated in the same device, revealing superconductivity below the transition temperature. These experimental results support that the pure spin current can be absorbed into a superconductive Nb wire with almost the same efficiency as in a normal state.

Experimental demonstration of a robust and scalable flux qubit

A novel rf-SQUID flux qubit that is robust against fabrication variations in Josephson junction critical currents and device inductance has been implemented. Measurements of the persistent current and of the tunneling energy between the two lowest lying states, both in the coherent and incoherent regime, are presented. These experimental results are shown to be in agreement with predictions of a quantum mechanical Hamiltonian whose parameters were independently calibrated, thus justifying the identification of this device as a flux qubit. In addition, measurements of the flux and critical current noise spectral densities are presented that indicate that these devices with Nb wiring are comparable to the best Al wiring rf-SQUIDs reported in the literature thusfar, with a $1/f$ flux noise spectral density at $1 $Hz of $1.3^{+0.7}_{-0.5} \mu\Phi_0/\sqrt{\text{Hz}}$. An explicit formula for converting the observed flux noise spectral density into a free induction decay time for a flux qubit biased to its optimal point and operated in the energy eigenbasis is presented.

Fabrication-process-induced variations ofNb/Al/AlOx/Nb Josephson junctions in superconductor integrated circuits

Currently, superconductor digital integrated circuits fabricated atHYPRES, Inc. can operate at clock frequencies approaching 40 GHz. Thecircuits present multilayered structures containing tens of thousands ofNb/Al/AlOx/Nb Josephson junctions (JJs) of various sizes interconnected by four Nb wiring layers,resistors, and other circuit elements. In order to be fully operational, the integratedcircuits should be fabricated such that the critical currents of the JJs are within thetight design margins and the proper relationships between the critical currents ofJJs of different sizes are preserved. We present experimental data and discussmechanisms of process-induced variations of the critical current and energy gap ofNb/Al/AlOx/Nb JJs in integrated circuits. We demonstrate that the Josephson critical current may dependon the type and area of circuit elements connected to the junction, on the circuit pattern,and on the step in the fabrication process at which the connection is made. In particular,we discuss the influence of (a) the junction base electrode connection to the groundplane, (b) the junction counter electrode connection to the ground plane, and(c) the counter electrode connection to the Ti/Au or Ti/Pd/Au contact padsby Nb wiring. We show that the process-induced changes of the properties ofNb/Al/AlOx/Nb junctions are caused by migration of impurity atoms (hydrogen) between the differentlayers comprising the integrated circuits.

A High-sensitivity Magnetocardiography System with 64 Axial Gradiometers Inside a Low Boil-off Dewar

Event Abstract Back to Event A High-sensitivity Magnetocardiography System with 64 Axial Gradiometers Inside a Low Boil-off Dewar Yong-Ho Lee1*, Kwon-Kyu Yu1, Hyukchan Kwon1, Jin-Mok Kim1 and Kiwoong Kim1 1 Korea Research Institute of Standards and Science, South Korea For accurate diagnosis and high-throughput screening of ischemic heart disease or arrhythmia, high-sensitivity economic MCG system is needed. We fabricated an MCG system having axial gradiometers with low stray pickup area and dewar with low boil-off rate of liquid He. The axial gradiometers have very simple structure for the superconductive connection. The two ends of pickup coil wires were placed near the input coil pads of SQUID, and annealed Nb wires were bonded directly between pickup coil wires and input coil pads. In this way, the stray pickup area (intrinsic balance) made by the connection structure is about 0.1 % of the pickup coil area, and the gradiometers can be operated inside a thin magnetically shielded room. The baseline of the first-order gradiometer is 70 mm, and diameter of pickup coil is 20 mm. The neck diameter of the dewar is smaller than the diameter of gradiometer array (dewar inner bottom). By dividing the gradiometer array into 4 plates, each plate can be installed separately into the dewar bottom. In this way, the boil-off rate of liquid He can be reduced to 3 L/day, for the inner bottom diameter of 280 mm. The SQUIDs are double relaxation oscillation SQUIDs with large flux-to-voltage transfer coefficients, enabling compact flux-locked loop electronics. The developed 64-channel system was installed inside a thin (80 mm thick) shielded room, and showed field noise level of 3 fT/sqrt(Hz) at 100 Hz. Measurements of adult and fetal MCG signals were done successfully using the developed system. Analysis software allows parameter analysis for the screening of ischemic heart disease and 3-dimensional imaging of myocardium current (reentry current source) on the realistic image of the heart. Conference: Biomag 2010 - 17th International Conference on Biomagnetism , Dubrovnik, Croatia, 28 Mar - 1 Apr, 2010. Presentation Type: Poster Presentation Topic: MCG: Instrumentation, Modeling, Basic and Clinical Studies Citation: Lee Y, Yu K, Kwon H, Kim J and Kim K (2010). A High-sensitivity Magnetocardiography System with 64 Axial Gradiometers Inside a Low Boil-off Dewar. Front. Neurosci. Conference Abstract: Biomag 2010 - 17th International Conference on Biomagnetism . doi: 10.3389/conf.fnins.2010.06.00367 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 08 Apr 2010; Published Online: 08 Apr 2010. * Correspondence: Yong-Ho Lee, Korea Research Institute of Standards and Science, Daejeon, South Korea, yhlee@kriss.re.kr Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Yong-Ho Lee Kwon-Kyu Yu Hyukchan Kwon Jin-Mok Kim Kiwoong Kim Google Yong-Ho Lee Kwon-Kyu Yu Hyukchan Kwon Jin-Mok Kim Kiwoong Kim Google Scholar Yong-Ho Lee Kwon-Kyu Yu Hyukchan Kwon Jin-Mok Kim Kiwoong Kim PubMed Yong-Ho Lee Kwon-Kyu Yu Hyukchan Kwon Jin-Mok Kim Kiwoong Kim Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

A high-sensitivity magnetocardiography system with a divided gradiometer array inside alow boil-off Dewar

We fabricated a low-noise 64-channel first-order axial gradiometer system for measuringmagnetocardiography (MCG) signals. The key technical features of the system are thecompact structure of the gradiometer, division of the sensor array plate, direct mounting ofthe sensor plates into the Dewar bottom, reduced neck diameter of the liquid He Dewar,and compact readout electronics. To make the refill interval of liquid He longer, thedistance between the compensation coil of the gradiometer and the input coil pads of thesuperconducting quantum interference device (SQUID) was reduced to 20 mm. By usingdirect ultrasonic bonding of Nb wires between the pickup coil wires and input coil pads,the superconductive connection structure became simple. The baseline of thefirst-order gradiometer is 70 mm, a little longer than for typical conventional axialgradiometers, to provide a larger signal amplitude for deep sources. The 64-channelgradiometer array consists of four blocks, and each block is fixed separately onto thebottom of the Dewar. The neck diameter of the He Dewar (192 mm) is smaller thanthe bottom diameter (280 mm) in which the gradiometers are distributed. Theaverage boil-off rate of the Dewar is 3 l per day when the 64-channel system is inoperation every day. Double relaxation oscillation SQUIDs (DROSs) having largeflux-to-voltage transfer coefficients were used to operate SQUIDs via compactelectronics. The magnetically shielded room (MSR) has a wall thickness of 80 mm, andconsists of two layers of permalloy and one layer of aluminum. When the 64-channelsystem was installed inside the MSR, the field noise level of the system was about3.5 fTrms Hz−1/2 at 100 Hz. MCG measurements with high signal quality were done successfullyusing the developed system. In addition to the parameter analysis method, wedeveloped software for the three-dimensional imaging of the myocardial currenton a realistic image of the heart based on the anatomical image of the torso.

Corrosion resistance of titanium-containing dental orthodontic wires in fluoride-containing artificial saliva

This study was to investigate the corrosion resistance of different Ti-containing dental orthodontic wires (including Ni–Ti, Ni–Ti–Cu, Ti–Mo–Zr–Sn, and Ti–Nb alloys) in acidic fluoride-containing artificial saliva using cyclic potentiodynamic polarization curve measurements. Different NaF concentrations (0%, 0.2%, and 0.5%), simulating the fluoride contents in commercial toothpastes, were added to the artificial saliva. Surface characterization was analyzed using X-ray photoelectron spectrometry. Cyclic potentiodynamic polarization curves showed that the presence of fluoride ions, especially 0.5% NaF, was detrimental to the protective ability of the TiO 2-based film on the Ti-containing wires. This might lead to a decrease in the corrosion resistance of the tested alloys, i.e. an increase in the corrosion rate and anodic current density and a decrease in the passive film breakdown potential. Among the tested Ti-containing wires, the Ni–Ti and Ni–Ti–Cu wires containing mainly TiO 2 on surface film were more susceptible to fluoride-enhanced corrosion, while the Ti–Mo–Zr–Sn and Ti–Nb wires containing MoO 3/ZrO 2/SnO and Nb 2O 5, respectively, along with TiO 2 on surface film were pitting corrosion resistant and showed a lower susceptibility to fluoride-enhanced corrosion. The difference in corrosion resistance of the tested commercial Ti-containing dental orthodontic wires was significantly dependent on the passive film characteristics on wires’ surface.

Measurement of MCG in Unshielded Environment Using a Second-Order SQUID Gradiometer

In this paper, we fabricated a low-TC second-order superconducting quantum interference device gradiometer (SQUID) to measure magnetocardiography (MCG) in unshielded environment. The second-order gradiometer consists of the pickup coil and the SQUID. The pickup coil is formed with two single-turn coils and one double-turn coil. The three coils are connected in order of single-, double-, and single-turn coil. The coupling polarity of two single coils is opposite to the double-turn coil. The SQUID is based on double relaxation oscillation SQUID (DROS), which consists of a hysteretic signal SQUID, a reference junction, and shunted a relaxation circuit with a resistor and an inductor. The DROS has ten times larger flux-to-voltage transfer coefficient (~ 1 mV/Phi0) than that of the conventional SQUID. Therefore, DROS could be operated with a simple flux-locked loop circuit. The pickup coil and the SQUID were fabricated on the independent wafers and connected superconductively using an Nb wire. The overall size of the second-order gradiometer is 94 times 12 mm2 with a baseline of 35 mm. The average field noise was about 8 fT /radicHz at 100 Hz with the second-order gradiometer in shielded or unshielded environment. The noise level is low enough to measure MCG signals in the unshielded environment. Finally, we measure the MCG in shielded and unshielded environments by using the second-order gradiometer and compared the signal characteristics measured in both environments.

Submicrometer ${\rm Nb}/{\rm Al}{-}{\rm AlO}_{\rm x}/{\rm Nb}$ Integrated Circuit Fabrication Process for Quantum Computing Applications

We have developed a low J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> (100-1000 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) submicrometer Nb integrated circuit fabrication process for SQUID-based quantum computing applications. The baseline process consists of 7 masking steps including Pd-Au resistor, Nb/Al-AlO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> /Nb trilayer, two Nb wiring layers and two sputtered SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> dielectric layers. We have also fabricated wafers with an Nb ground plane. Using deep-UV lithography, inductively coupled plasma etch tools, and self-aligned lift-off for device definition, we routinely achieve micrometer lines and spaces with 400 nm minimum junction dimensions. Room temperature testing is used to select wafers in process and junction annealing has been calibrated for trimming current density. We will describe the process which has been used to produce circuits with over 100 junctions.

Fabrication of Submicrometer High Current Density ${\hbox{ Nb/Al-AlN}}_{\rm x}/{\hbox{ Nb}}$ Junctions

We have developed a sub-mum Nb/Al-AlNx/Nb Josephson junction and integrated circuit fabrication process using deep-UV lithography and inductively coupled plasma etch tools. The baseline process consists of 11 masking steps including ground plane, PdAu resistor, Nb/Al-AlNx/Nb trilayer, and two additional Nb wiring layers. The AlNx tunnel barriers are grown with plasma nitridation. These junctions exhibit low subgap leakage even at current densities exceeding 100 kA/cm2. The critical current spread of a series array of 50- kA/cm2, 0.6 mum diameter junctions is under 3%. For very high current density applications, these junctions are a good candidate to replace Nb/Al-AlOx/Nb junctions particularly in future generations of very high speed, rapid single flux quantum logic circuits. In this paper we discuss our baseline fabrication process and device characterization including junction capacitance extraction from direct measurements of the Josephson plasma frequency.

Investigation of vortex structures in a current-carrying Nb wire

We describe small angle neutron scattering measurements of the vortex structure within acurrent-carrying wire in the presence of a longitudinal magnetic field. This situationinvolves the combined effects of the applied field and the self-field of the current and hasattracted a great deal of theoretical and experimental work as exotic helical vortexstructures have been predicted. We find that the voltage characteristics, a complete absenceof spreading of the Bragg peaks and loss of scattered intensity with increasingcurrent are inconsistent with a helical vortex state. Our data are qualitativelyconsistent with a model where the crossing of self-field loops with vortex linesresults in a ring of kinks leaving the remaining longitudinal lattice unperturbed.

Meissner Effect in Superconducting Microtraps

We report on the realization and characterization of a magnetic microtrap for ultracold atoms near a straight superconducting Nb wire with circular cross section. The trapped atoms are used to probe the magnetic field outside the superconducting wire. The Meissner effect shortens the distance between the trap and the wire, reduces the radial magnetic-field gradients, and lowers the trap depth. Measurements of the trap position reveal a complete exclusion of the magnetic field from the superconducting wire for temperatures lower than 6 K. As the temperature is further increased, the magnetic field partially penetrates the superconducting wire; hence the microtrap position is shifted towards the position expected for a normal-conducting wire.

In situ Neutron Diffraction Study of Internal Micro‐Stresses Developed by Plastic Elongation in &amp;&amp;num;60;110&amp;&amp;num;62; Textured BCC Wires

By in situ neutron diffraction during tensile tests of a strongly <100> textured Nb wire, we have shown the development of internal tensile microstresses of the order of 20 % of the flow stress, acting normal to the longitudinally aligned {110} planes. Such stresses are retained as residual stresses upon unloading. They must be taken into account for preventing splitting failures of high strength BCC wires (e.g., highly drawn tungsten filaments or pearlitic steel wires) that, because of the drawing fabrication process, contain a high density of longitudinally oriented brittle interfaces.