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Characterization and Coil Test Results for a Multifilamentary NbTi Conductor Utilizing Artificial Pinning Center Technology

Description: The introduction of pinning centers via the controlled addition of a second phase, with the correct size and spacing, has been proposed as a method for producing a material with optimum flux pinning and hence a higher critical current density in practical superconductors. The demonstration of such artificial pinning center (APC) materials has been the aim of recent collaborative efforts with several U.S. manufacturers. This paper reports the coil test results for a multifilamentary NbTi conductor fabricated using an APC technique. The conductor showed improved performance compared to earlier APC conductors, and its performance is comparable to that found in conventional multifilamentary NbTi conductors. In addition to coil test results, the paper will report on the low field magnetization, SEM, and TEM studies, and the results will be compared with similar results on conventional NbTi.
Date: August 1, 1992
Creator: Scanlan, R.M.; Dietderich, D.; Ghiorso, W. & McManaman, P.
Partner: UNT Libraries Government Documents Department

Switching a magnetic vortex by interlayer coupling in epitaxially grown Co/Cu/Py/Cu(001) trilayer disks

Description: Epitaxial Py/Cu/Co/Cu(001) trilayers were patterned into micron sized disks and imaged using element-specific photoemission electron microscopy. By varying the Cu spacer layer thickness, we study how the coupling between the two magnetic layers influences the formation of magnetic vortex states. We find that while the Py and Co disks form magnetic vortex domains when the interlayer coupling is ferromagnetic, the magnetic vortex domains of the Py and Co disks break into anti-parallel aligned multidomains when the interlayer coupling is antiferromagnetic. We explain this result in terms of magnetic flux closure between the Py and Co layers for the antiferromagnetic coupling case.
Date: July 16, 2010
Creator: Wu, J.; Carlton, D.; Oelker, E.; Park, J. S.; Jin, E.; Arenholz, E. et al.
Partner: UNT Libraries Government Documents Department

Nonlinear motion of coupled magnetic vortices in ferromagnetic/non-magnetic/ferromagnetic trilayer

Description: We have investigated a coupled motion of two vortex cores in ferromagnetic/nonmagnetic/ferromagnetic trilayer cynliders by means of micromagnetic simulation. Dynamic motion of two vortex with parallel and antiparallel relative chiralities of curling spins around the vortex cores have been examined after excitation by 1-ns pulsed external field. With systematic variation in non-magnetic spacer layer thickness from 0 to 20 nm, the coupling between two cores becomes significant as the spacer becomes thinner. Significant coupling leads to a nonlinear chaotic coupled motion of two vortex cores for the parallel chiralities and a faster coupled gyrotropic oscillation for the antiparallel chiralities.
Date: July 5, 2009
Creator: Jun, Su-Hyeong; Shim, Je-Ho; Oh, Suhk-Kun; Yu, Seong-Cho; Kim, Dong-Hyun; Mesler, Brooke et al.
Partner: UNT Libraries Government Documents Department

Comment on flux creep with logarithmic U(j) dependence

Description: The numerical calculation by Wang and Dong [Phys. Rev. B 49, 698 (1994)] of flux density profiles across a slab sample exposes a possible misunderstanding of the solution given earlier by vinokur, Feigel`man and Geshkenbein, but also predicts a kink in the magnetization relaxation curve which Schnack and Griessen have already shown to be erroneous.
Date: February 1, 1994
Creator: Gilchrist, J.; Schnack, H.G. & van der Beek, C.J.
Partner: UNT Libraries Government Documents Department

HTS generator assessment. Final report, DOE SPI-Phase I: Task I

Description: The intention of this work was to continue the superconducting generator work that was terminated in the eighties. The generator design concept employs a sc generator rotor winding and aims at capitalizing fully on the very high magnetic flux density in the generator air gap now possible through the use of superconductivity in the generator field.
Date: October 1, 1995
Creator: Cotzas, G.
Partner: UNT Libraries Government Documents Department

A Premliminary Report on Strength of 1/2 of a 3Q120

Description: Attached please find some data taken on the dates show at MTF on a 3Q12OA magnet by utilizing a Morgan Coil for determining the strength of the quadrupole component. The probe was inserted approximately 1/2 the distance through the magnet (accuracy of longitudinal placement about .25 inch) and was rotated to record the flux change at constant current. The data are listed twice: once in time order and once sorted by current. It should be noted that these measurements were begun when the magnet had not ever been powered and the initial flux was very small. The remanent after a 400 A excitation is also available in these results. As a guide to the activity planned for each measurement, Table 3 lists with each run the title created by the measurer. these results are plotted in Figures 1-3. This magnet is marked as No.4 and to match the MTF VAX measurement system conventions, it was labeled as QGGOO4 in the data. The analysis of strength is based on a nominal probe radius determined from shop drawings. The amplitude of the quadrupole component is converted to Tesla-m/m of strength in the regular data reduction program. It is reported in the frame in which the skew quadrupole component is zero. The data is taken with the current measured at the Transductor. This is known to be an inferior method of current measurement below about 50 A. The author has not corrected the data, but a special calibration against the shunt was carried out.
Date: April 12, 1985
Creator: Brown, B.
Partner: UNT Libraries Government Documents Department

Characteristics of round and extracted strands of Nb3Al Rutherford cable

Description: Long Nb{sub 3}Al strands with copper stabilizer are promising for future high field accelerator magnets. A 1.2 kilometer Nb{sub 3}Al strand with Cu stabilizer was fabricated at the National Institute for Materials Science in Japan. Using this strand a 30 meter Cu stabilized Nb{sub 3}Al Rutherford cable was made for the first time by a collaboration of NIMS and Fermilab. The Nb{sub 3}Al strands extracted from cable with a relatively low packing factor showed almost no J{sub c} degradation. But the extracted strands from the highly compacted cable showed some degradation in both J{sub c} and n value, which may be caused by local separation of the copper stabilizer. Still, its J{sub c} degradation is lower than that of typical Nb{sub 3}Sn strands. The current limit due to magnetic instability in low field is about 500 A at 4.2 K. The magnetization of the strands, which was measured with balanced coils at 4.2 K, showed large flux jumps, usually around 1.5 T. This value is much larger than the B{sub c2} (4.2 K) of the Nb matrix, which is around 0.4 Tesla. The magnetic instability of the Nb{sub 3}Al strand at low field is not completely understood, but it might be explained by the superconducting coupling current through the Nb matrix.
Date: August 1, 2006
Creator: Kikuchi, A.; Yamada, R.; Ambrosio, G.; Andreev, N.; Barzi, E.; Cooper, C. et al.
Partner: UNT Libraries Government Documents Department

New experimental capabilities and theoretical insights of high pressure compression waves

Description: Currently there are three platforms that offer quasi-isentropic compression or ramp-wave compression (RWC): light-gas gun, magnetic flux (Z-pinch), and laser. We focus here on the light-gas gun technique and on some current theoretical insights from experimental data. A gradient impedance through the length of the impactor provides the pressure pulse upon impactor to the subject material. Applications and results are given concerning high-pressure strength and liquid to solid, phase transition of water plus its associated phase fraction history. We also introduce the Korteweg-deVries-Burgers equation as a means to understand the evolution these RWC waves that propagate through the thickness of the subject material. This equation has the necessary competition between non-linear, dispersion, and dissipation processes, which is shown through observed structures that are manifested in the experimental particle velocity histories. Such methodology points towards a possible quantifiable dissipation, through which RWC experiments may be analyzed.
Date: July 20, 2007
Creator: Orlikowski, D; Nguyen, J; Patterson, J R; Minich, R; Martin, L P & Holmes, N
Partner: UNT Libraries Government Documents Department

Quench tests and FEM analysis of Nb3Al Rutherford cables and small racetrack magnets

Description: In collaboration between NIMS and Fermilab, we have made copper stabilized Nb{sub 3}Al Rutherford cables, using Nb-matrixed and Ta-matrixed strands. First these cables were investigated at high current in low self field using a flux pump. Using these Rutherford cables, we built and tested small racetrack magnets. The magnet made with the Nb-matrixed strand showed the flux jump instability in low field. The small racetrack magnet wound with the Ta-matrixed Nb{sub 3}Al Rutherford cable was very stable at 4.5 K operation without any instability, as well as at 2.2 K operation. With the successful operation of the small racetrack magnet up to its short sample data, the feasibility of the Nb{sub 3}Al strand and its Rutherford cable for their application to high field magnets is established. The characteristics of Nb{sub 3}Al Rutherford cable is compared with that of the Nb{sub 3}Sn Rutherford cable and the advantages of Nb{sub 3}Al Rutherford cable are discussed.
Date: December 1, 2008
Creator: Yamada, R.; Kikuchi, A.; Chlachidze, G.; Ambrosio, G.; Andreev, N.; Barzi, E. et al.
Partner: UNT Libraries Government Documents Department

Vortices wiggled and dragged

Description: When a sufficiently strong magnetic field is applied to a superconductor, some of the field can pierce it through the generation of magnetic vortices, each of which contains a quantized amount of magnetic flux. Although the superconducting state of the material outside each vortex is maintained (and destroyed within each vortex), the interaction of vortices with a current passing through the material can cause them to move, dissipating energy and thereby generating a source of electrical resistance. The ability to manipulate an individual superconducting vortex represents a powerful tool for studying the dynamics of vortices and the superconductors that support them. It could also lead to the development of a new class of fluxon-based electronics.
Date: January 1, 2008
Creator: Reichhardt, Charles
Partner: UNT Libraries Government Documents Department

RRP Nb3Sn Strand Studies for LARP

Description: The Nb{sub 3}Sn strand chosen for the next step in the magnet R&D of the U.S. LHC Accelerator Research Program is the 54/61 sub-element Restacked Rod Process by Oxford Instruments, Superconducting Technology. To ensure that the 0.7 mm RRP strands to be used in the upcoming LARP magnets are suitable, extensive studies were performed. Measurements included the critical current, I{sub c}, using the voltage-current (V-I) method, the stability current, I{sub S}, as the minimal quench current obtained with the voltage-field (V-H) method, and RRR. Magnetization was measured at low and high fields to determine the effective filament size and to detect flux jumps. Effects of heat treatment temperature and durations on I{sub c} and I{sub S} were also studied. Using strand billet qualification and tests of strands extracted from cables, the short sample limits of magnet performance were obtained. The details and the results of this investigation are herein described.
Date: June 1, 2007
Creator: Barzi, Emanuela; Bossert, Rodger; Caspi, Shlomo; Dietderich, Daniel R.; Ferracin, Paolo; Ghosh, Arup et al.
Partner: UNT Libraries Government Documents Department

Correlation Between Strand Stability and Magnet Performance

Description: Magnet programs at BNL, LBNL and FNAL have observed instabilities in high J{sub c} Nb{sub 3}Sn strands and magnets made from these strands. This paper correlates the strand stability determined from a short sample-strand test to the observed magnet performance. It has been observed that strands that carry high currents at high fields (greater than 10 T) cannot sustain these same currents at low fields (1-3 T) when the sample current is fixed and the magnetic field is ramped. This suggests that the present generation of strand is susceptible to flux jumps (FJ). To prevent flux jumps from limiting stand performance, one must accommodate the energy released during a flux jump. To better understand FJ this work has focused on wire with a given sub-element diameter and shows that one can significantly improve stability by increasing the copper conductivity (higher residual resistivity ratio, RRR, of the Cu). This increased stability significantly improves the conductor performance and permits it to carry more current.
Date: June 1, 2005
Creator: Dietderich, D.R.; Bartlett, S.E.; Caspi, S.; Ferracin, P.; Gourlay, S.A.; Higley, H.C. et al.
Partner: UNT Libraries Government Documents Department

Voltage spikes in Nb3Sn and NbTi strands

Description: As part of the High Field Magnet program at Fermilab several NbTi and Nb{sub 3}Sn strands were tested with particular emphasis on the study of voltage spikes and their relationship to superconductor instabilities. The voltage spikes were detected under various experimental conditions using voltage-current (V-I) and voltage-field (V-H) methods. Two types of spikes, designated ''magnetization'' and ''transport current'' spikes, have been identified. Their origin is most likely related to magnetization flux jump and transport current redistribution, respectively. Many of the signals observed appear to be a combination of these two types of spikes; the combination of these two instability mechanisms should play a dominant role in determining the minimum quench current.
Date: September 1, 2005
Creator: Bordini, B.; Ambrosio, G.; Barzi, E.; Carcagno, R.; Feher, S.; Kashikhin, V.V. et al.
Partner: UNT Libraries Government Documents Department

Systematic changes of the Nb-Sn reaction with time, temperature and alloying in Restacked-Rod-Process (RRP) Nb3Sn strands

Description: Reaction heat treatments spanning 605 to 750 C and 24 to {approx}400 hours were applied to several sets of RRP strands. Magnetization and transport measurements were used to track the changes of superconducting properties and the amounts of Nb{sub 3}Sn formed. The experiments showed that temperature increases of 15 C produced equivalent properties in half the time within the temperature range 620-680 C. This result was the same whether Ta or Ti was used to alloy the Nb{sub 3}Sn. The bulk pinning force Fp for Ta-alloyed wires displayed a significant drop for temperatures outside the range above, due to tin gradients at low temperatures and grain growth at high temperatures. The F{sub p} drop at high reaction temperatures prevents wire technology from taking advantage of significantly higher Kramer-plot intercept H{sub K} for high-temperature reactions. On the other hand, Ti alloying provides a quick and potent means to increase H{sub K} at reaction temperatures for which F{sub p} remains high.
Date: September 1, 2008
Creator: Ghosh, A.K.; Sperry, E.A.; D'Ambra, J.; /Brookhaven; Cooley, L.D. & /Fermilab
Partner: UNT Libraries Government Documents Department

Correlation between Strand Stability and Magnet Performance

Description: Magnet programs at BNL, LBNL and FNAL have observed instabilities in high J{sub c} Nb{sub 3}Sn strands and magnets made from these strands. This paper correlates the strand stability determined from a short sample-strand test to the observed magnet performance. It has been observed that strands that carry high currents at high fields (greater than 10T) cannot sustain these same currents at low fields (1-3T) when the sample current is fixed and the magnetic field is ramped. This suggests that the present generation of strand is susceptible to flux jumps (FJ). To prevent flux jumps from limiting stand performance, one must accommodate the energy released during a flux jump. To better understand FJ this work has focused on wire with a given sub-element diameter and shows that one can significantly improve stability by increasing the copper conductivity (higher residual resistivity ratio, RRR, of the Cu). This increased stability significantly improves the conductor performance and permits it to carry more current.
Date: April 16, 2005
Creator: Dietderich, Daniel R.; Bartlett, Scott E.; Caspi, Shlomo; Ferracin, Paolo; G ourlay, Stephen A.; Higley, Hugh C. et al.
Partner: UNT Libraries Government Documents Department

Magnetic core studies at LBNL and LLNL

Description: The objective of this work is to minimize the cost of the materials and maximize the performance of magnetic cores, a major cost component of a Heavy-Ion-Fusion, HIF, induction accelerator driver. This includes selection of the alloy for cost and performance, and maximizing the performance of each alloy evaluated. The two major performance parameters are the magnetic flux swing and the energy loss. The volt seconds of the cores, obtained from the flux swing with Faraday's Law, determines the beam energy and duration. Core losses from forming domains and moving their boundaries are a major factor in determining the efficiency of an induction accelerator.
Date: September 20, 1997
Creator: Molvik, A.W.; Faltens, A.; Reginato, L.; Blaszkiewicz, M.; Smith, C. & Wood, R.
Partner: UNT Libraries Government Documents Department

Superconducting nanostructured materials.

Description: Within the last year it has been realized that the remarkable properties of superconducting thin films containing a periodic array of defects (such as sub-micron sized holes) offer a new route for developing a novel superconducting materials based on precise control of microstructure by modern photolithography. A superconductor is a material which, when cooled below a certain temperature, loses all resistance to electricity. This means that superconducting materials can carry large electrical currents without any energy loss--but there are limits to how much current can flow before superconductivity is destroyed. The current at which superconductivity breaks down is called the critical current. The value of the critical current is determined by the balance of Lorentz forces and pinning forces acting on the flux lines in the superconductor. Lorentz forces proportional to the current flow tend to drive the flux lines into motion, which dissipates energy and destroys zero resistance. Pinning forces created by isolated defects in the microstructure oppose flux line motion and increase the critical current. Many kinds of artificial pinning centers have been proposed and developed to increase critical current performance, ranging from dispersal of small non-superconducting second phases to creation of defects by proton, neutron or heavy ion irradiation. In all of these methods, the pinning centers are randomly distributed over the superconducting material, causing them to operate well below their maximum efficiency. We are overcome this drawback by creating pinning centers in aperiodic lattice (see Fig 1) so that each pin site interacts strongly with only one or a few flux lines.
Date: July 13, 1998
Creator: Metlushko, V.
Partner: UNT Libraries Government Documents Department

Vortices in dense self-assembled hole arrays.

Description: We present a study of the upper critical field and pinning strength from the resistivity and magnetization of a Nb film containing a dense array of 45 nm diameter holes on a hexagonal lattice with a spacing of 101 nm. The holes were formed by self-assembly in anodic aluminum oxide (AAO) using an electrochemical procedure. Confinement effects and Little-Parks oscillations are seen above 6 K, and strong pinning with matching field effects is seen below 6 K. Above the first matching field interstitial vortices coexist with vortices trapped in the hole array. Pinning in the Nb films with hole arrays is enhanced by two orders of magnitude over that in continuous Nb films. At low temperature, flux avalanches are observed and imaged using the magneto-optical Faraday effect.
Date: October 9, 2002
Creator: Crabtree, G. W.; Welp, U.; Xiao, Z. L.; Jiang, J. S.; Vlasko-Vlasov, V. K.; Bader, S. D. et al.
Partner: UNT Libraries Government Documents Department

Voltage-probe-position dependence and magnetic-flux contribution to the measured voltage in ac transport measurements: which measuring circuit determines the real losses?

Description: The voltage V{sub ab} measured between two voltage taps a and b during magnetic flux transport in a type-II superconductor carrying current I is the sum of two contributions, the line integral from a to b of the electric field along an arbitrary path C{sub s} through the superconductor and a term proportional to the time rate of change of magnetic flux through the area bounded by the path C{sub s} and the measuring circuit leads. When the current I(t) is oscillating with time t, the apparent ac loss (the time average of the product IV{sub ab}) depends upon the measuring circuit used. Only when the measuring-circuit leads are brought out far from the surface does the apparent power dissipation approach the real (or true) ac loss associated with the length of sample probed. Calculations showing comparisons between the apparent and real ac losses in a flat strip of rectangular cross section will be presented, showing the behavior as a function of the measuring-circuit dimensions. Corresponding calculations also are presented for a sample of elliptical cross section.
Date: December 31, 1995
Creator: Pe, T.; McDonald, J. & Clem, J.R.
Partner: UNT Libraries Government Documents Department

BaBar technical design report: Chapter 9, Magnet coil and flux return

Description: The BaBar magnet is a thin, 1.5 T superconducting solenoid with a hexagonal flux return. This chapter discusses the physics requirements and performance goals for the magnet, describes key interfaces, and summarizes the projected magnet performance. It also presents the design of the superconducting solenoid, including magnetic design, cold mass design, quench protection and stability, cold mass cooling, cryostat design, and coil assembly and transportation. The cryogenic supply system and instrumentation are described briefly, and the flux return is described.
Date: March 1, 1995
Creator: O`Connor, T. & Collaboration, The BaBar
Partner: UNT Libraries Government Documents Department

Digital signal processing control of induction machine`s torque and stator flux utilizing the direct stator flux field orientation method

Description: This paper presents a review of the Direct Stator Flux Field Orientation control method. This method can be used to control an induction motor`s torque and flux directly and is the application of interest for this thesis. This control method is implemented without the traditional feedback loops and associated hardware. Predictions are made, by mathematical calculations, of the stator voltage vector. The voltage vector is determined twice a switching period. The switching period is fixed throughout the analysis. The three phase inverter duty cycle necessary to control the torque and flux of the induction machine is determined by the voltage space vector Pulse Width Modulation (PWM) technique. Transient performance of either the flux or torque requires an alternate modulation scheme which is also addressed in this thesis. A block diagram of this closed loop system is provided. 22 figs., 7 tabs.
Date: April 1, 1997
Creator: Seiz, J.B.
Partner: UNT Libraries Government Documents Department

Imaging systems for biomedical applications. Final report

Description: Many of the activities of the human body manifest themselves by the presence of a very weak magnetic field outside the body, a field that is so weak that an ultra-sensitive magnetic sensor is needed for specific biomagnetic measurements. Superconducting QUantum Interference Devices (SQUIDs) are extremely sensitive detectors of magnetic flux and have been used extensively to detect the human magnetocardiogram, and magnetoencephalogram. and other biomagnetic signals. In order to utilize a SQUID as a magnetometer, its transfer characteristics should be linearized. This linearization requires extensive peripheral electronics, thus limiting the number of SQUID magnetometer channels in a practical system. The proposed digital SQUID integrates the processing circuitry on the same cryogenic chip as the SQUID magnetometer and eliminates the sophisticated peripheral electronics. Such a system is compact and cost effective, and requires minimal support electronics. Under a DOE-sponsored SBIR program, we designed, simulated, laid out, fabricated, evaluated, and demonstrated a digital SQUID magnetometer. This report summarizes the accomplishments under this program and clearly demonstrates that all of the tasks proposed in the phase II application were successfully completed with confirmed experimental results.
Date: June 6, 1995
Creator: Radparvar, M.
Partner: UNT Libraries Government Documents Department