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Potential impact of high temperature superconductors on maglev transportation

Description: This report describes the potential impact that high-temperature superconductors (HTSs) may have on transportation by magnetically levitated vehicles. It is not intended as a planning document, but rather as an overview of potential HTS applications to magnetic-levitation (maglev) transportation. The present maglev program in the United States is summarized, and the present status of development of HTSs is described. Areas identified for possible impact on maglev technology are (1) liquid-nitrogen-cooled levitation magnets, (2) magnetic-field shielding of the passenger compartment, (3) superconducting magnetic energy storage for wayside power, (4) superconducting bearings for flywheel energy storage for wayside power, (5) downleads to continuously powered liquid-helium-cooled levitation magnets, and (6) liquid-hydrogen-cooled levitation magnets and linear motor propulsion windings. Major technical issues that remain to be resolved for the use of HTSs in maglev applications include thermal magnetic stability, mechanical properties, and critical current density at liquid-nitrogen temperatures.
Date: February 1, 1992
Creator: Hull, J.R.
Partner: UNT Libraries Government Documents Department

Applications of bulk high-temperature superconductors

Description: The development of high-temperature superconductors (HTSs) can be broadly generalized into thin-film electronics, wire applications, and bulk applications. We consider bulk HTSs to include sintered or crystallized forms that do not take the geometry of filaments or tapes, and we discuss major applications for these materials. For the most part applications may be realized with the HTSs cooled to 77 K, and the properties of the bulk HTSs are often already sufficient for commercial use. A non-exhaustive list of applications for bulk HTSs includes trapped field magnets, hysteresis motors, magnetic shielding, current leads, and magnetic bearings. These applications are briefly discussed in this paper.
Date: June 1, 1995
Creator: Hull, J.R.
Partner: UNT Libraries Government Documents Department

Competition between SMES and flywheels

Description: The benefits of flywheel energy storage using high-temperature superconducting bearings is compared to that of SMES for the same applications. Flywheels cover the same range of energy storage times as SMES but their scaling relationships make them inherently more amenable to modular manufacture. In addition, the magnetic fields seen by the environment are considerably reduced for flywheels.
Date: February 1, 1995
Creator: Hull, J.R.
Partner: UNT Libraries Government Documents Department

Effect of permanent-magnet irregularities in levitation force measurements.

Description: In the measurement of the levitation force between a vertically magnetized permanent magnet (PM) and a bulk high-temperature superconductor (HTS), PM domains with horizontal components of magnetization are shown to produce a nonnegligible contribution to the levitation force in most systems. Such domains are typically found in all PMs, even in those that exhibit zero net horizontal magnetic moment. Extension of this analysis leads to an HTS analog of Earnshaw's theorem, in which at the field-cooling position the vertical stiffness is equal to the sum of the horizontal stiffnesses, independent of angular distribution of magnetic moments within the PM.
Date: October 14, 1999
Creator: Hull, J. R.
Partner: UNT Libraries Government Documents Department

Gravimeter using high-temperature superconductor bearing.

Description: We have developed a sensitive gravimeter concept that uses an extremely low-friction bearing based on a permanent magnet (PM) levitated over a high-temperature superconductor (HTS). A mass is attached to the PM by means of a cantilevered beam, and the combination of PM and HTS forms a bearing platform that has low resistance to rotational motion but high resistance to horizontal, vertical, or tilting motion. The combination acts as a low-loss torsional pendulum that can be operated in any orientation. Gravity acts on the cantilevered beam and attached mass, accelerating them. Variations in gravity can be detected by time-of-flight acceleration, or by a control coil or electrode that would keep the mass stationary. Calculations suggest that the HTS gravimeter would be as sensitive as present-day superconducting gravimeters that need cooling to liquid helium temperatures, but the HTS gravimeter needs cooling only to liquid nitrogen temperatures.
Date: September 11, 1998
Creator: Hull, J. R.
Partner: UNT Libraries Government Documents Department

Trapped-flux internal-dipole superconducting motor/generator.

Description: A new class of motor/generator (M/G) utilizes the magnetic flux trapping capability of high-temperature superconductors (HTSs). The rotor, consists of a cylindrical shell composed of HTS segments. These segments act as trapped-field magnets, magnetized in such a way that a dipole magnetic field is produced in the interior of the shell. A stator coil assembly is placed in the interior of the shell and current passing through the conductors of the coil produce a rotational torque, either as a hysteresis motor or as a synchronous motor. The coil may be either conventional, with copper wires and an iron core, or composed of superconductors and can be used to establish the trapped fields in the HTSs.
Date: September 3, 1998
Creator: Hull, J. R.
Partner: UNT Libraries Government Documents Department

Potential for use of high-temperature superconductors in fusion reactors

Description: The present rate of development of high-temperature superconductors (HTSs) is sufficiently rapid that there may be opportunities for their use in contemporary fusion devices such as the International Thermonuclear Experimental Reactor (ITER). The most likely 1application is for delivering power to the superconducting magnets, especially in substituting for the current leads between the temperatures of 4 K and 77K. A second possible application of HTSs is as a liquid-nitrogen-cooled power bus, connecting the power supplies to the magnets, thus reducing the ohmic heating losses over these relatively long cables. A third potential application of HTSs is as an inner high-field winding of the toroidal field coils that would operate at {approx}20 K. While the use of higher temperature magnets offers significant advantages to the reactor system, it is unlikely that tested conductors of this type will be available within the ITER time frame. 23 refs., 2 figs.
Date: January 1, 1991
Creator: Hull, J.R.
Partner: UNT Libraries Government Documents Department

Use of thin films in high-temperature superconducting bearings.

Description: In a PM/HTS bearing, locating a thin-film HTS above a bulk HTS was expected to maintain the large levitation force provided by the bulk with a lower rotational drag provided by the very high current density of the film. For low drag to be achieved, the thin film must shield the bulk from inhomogeneous magnetic fields. Measurement of rotational drag of a PM/HTS bearing that used a combination of bulk and film HTS showed that the thin film is not effective in reducing the rotational drag. Subsequent experiments, in which an AC coil was placed above the thin-film HTS and the magnetic field on the other side of the film was measured, showed that the thin film provides good shielding when the coil axis is perpendicular to the film surface but poor shielding when the coil axis is parallel to the surface. This is consistent with the lack of reduction in rotational drag being due to a horizontal magnetic moment of the permanent magnet. The poor shielding with the coil axis parallel to the film surface is attributed to the aspect ratio of the film and the three-dimensional nature of the current flow in the film for this coil orientation.
Date: September 30, 1999
Creator: Hull, J. R. & Cansiz, A.
Partner: UNT Libraries Government Documents Department

Magnetically levitated space elevator to low-earth orbit.

Description: The properties of currently available NbTi superconductor and carbon-fiber structural materials enable the possibility of constructing a magnetically levitated space elevator from the earth's surface up to an altitude of {approx} 200 km. The magnetic part of the elevator consists of a long loop of current-carrying NbTi, composed of one length that is attached to the earth's surface in an east-west direction and a levitated-arch portion. The critical current density of NbTi is sufficiently high that these conductors will stably levitate in the earth's magnetic field. The magnetic self-field from the loop increases the levitational force and for some geometries assists levitational stability. The 200-km maximum height of the levitated arch is limited by the allowable stresses of the structural material. The loop is cryogenically cooled with helium, and the system utilizes intermediate pumping and cooling stations along both the ground and the levitated portion of the loop, similar to other large terrestrial cryogenic systems. Mechanically suspended from the basic loop is an elevator structure, upon which mass can be moved between the earth's surface and the top of the loop by a linear electric motor or other mechanical or electrical means. At the top of the loop, vehicles may be accelerated to orbital velocity or higher by rocket motors, electromagnetic propulsion, or hybrid methods.
Date: July 2, 2001
Creator: Hull, J. R. & Mulcahy, T. M.
Partner: UNT Libraries Government Documents Department

A superconducting solenoid and press for permanent magnet fabrication.

Description: For the first time, a superconducting solenoid (SCM) was used to increase the remnant magnetization of sintered NdFeB permanent magnets (PMs). In particular, improved magnetic alignment of commercial-grade PM powder was achieved, as it was axial die pressed into 12.7-mm diameter cylindrical compacts in the 76.2-mm warm bore of a 9-T SCM. The press used to compact the powder is unique and was specifically designed for use with the SCM. Although the press was operated in the batch mode for this proof of concept study, its design is intended to enable automated production. In operation, a simple die and punch set made of nonmagnetic materials was filled with powder and loaded into a nonmagnetic press tube. The cantilevered press tube was inserted horizontally, on a carrier manually advanced along a track, into the SCM. The robustness of the mechanical components and the SCM, in its liquid helium dewar, were specifically designed to allow for insertion and extraction of the magnetic powder and compacts, while operating at 9 T. Compaction was achieved by pressing the punches between the closed end of the press tube and the hydraulic cylinder mounted on the opposite end. Improvements up to 10% in magnetization and 20% in energy products of the permanent magnets were obtained, as the alignment fields were increased above the 2-T maximum field of the electromagnets used in industry. Increases in magnetization of 3% are significant in the mature sintered magnet industry.
Date: July 16, 2002
Creator: Mulcahy, T. M. & Hull, J. R.
Partner: UNT Libraries Government Documents Department

Recent advances in high-temperature superconductor wire fabrication and applications development

Description: In this paper, recent advances in fabrication of HTS wires are summarized, and detailed discussion is provided for developments in near- and intermediate-term applications. Near-term applications, using presently obtainable current densities, include: liquid-nitrogen depth sensors, cryostat current leads, and magnetic bearings. Intermediate-term applications, using current densities expected to be available in the near future include fault-current limiters and short transmission lines. 25 refs.
Date: January 1, 1992
Creator: Hull, J.R. & Uherka, K.L.
Partner: UNT Libraries Government Documents Department

High-temperature superconductor applications development at Argonne National Laboratory

Description: Developments at Argonne National Laboratory of near and intermediate term applications using high-temperature superconductors are discussed. Near-term applications of liquid-nitrogen depth sensors, current leads, and magnetic bearings are discussed in detail.
Date: February 9, 1992
Creator: Hull, J.R. & Poeppel, R.B.
Partner: UNT Libraries Government Documents Department

NdFeB magnets aligned in a 9-T superconducting solenoid.

Description: Commercial-grade magnet powder (Magnequench UG) was uniaxial die-pressed into cylindrical compacts, while being aligned in the 1-T to 8-T DC field of a superconducting solenoid at Argonne National Laboratory. Then, the compacts were added to normal Magnequench UG production batches for sintering and annealing. The variations in magnet properties for different strengths of alignment fields are reported for 15.88-mm (5/8-in.) diameter compacts made with length-to-diameter (L/D) ratios in the range {ge} 0.25 and {le} 1. The best magnets were produced when the powder-filled die was inserted into the active field of the solenoid and then pressed. Improvements in the residual flux density of 8% and in the energy product of 16% were achieved by increasing the alignment field beyond the typical 2-T capabilities of electromagnets. The most improvement was achieved for the compacts with the smallest L/D ratio. The ability to make very strong magnets with small L/D, where self-demagnetization effects during alignment are greatest, would benefit most the production of near-final-shape magnets. Compaction of the magnet powder using a horizontal die and a continuously active superconducting solenoid was not a problem. Although the press was operated in the batch mode for this proof-of-concept study, its design is intended to enable automated production.
Date: May 8, 2002
Creator: Mulcahy, T. M.; Hull, J. R.; Rozendaal, E. & Wise, J. H.
Partner: UNT Libraries Government Documents Department

Optimization of high-temperature superconductor current leads

Description: Methods to improve the performance of high-temperature superconducting current leads are analyzed. Designs are considered that are inherently safe from burnup, even if the lead enters the normal state. The effect of a tapered lead that takes advantage of the increase in critical current density with decreasing temperature will decrease helium boiloff by about a factor of two for an area ratio of four. A new concept, in which Ag powder is distributed in increasing concentration from the cold end to the hot end of the lead in sintered YBCO, is shown to have comparable performance to that of leads made with Ag-alloy sheaths. Performance of the best inherently safe designs is about one order of magnitude better than that of optimized nonsuperconducting leads. BSCCO leads with Ag-alloy sheaths show improved performance for Au fractions up to about 3%, after which increases in Au fraction yield negligible performance improvement.
Date: February 1, 1995
Creator: Seol, S.Y.; Hull, J.R. & Chyu, M.C.
Partner: UNT Libraries Government Documents Department

Prediction of burnout of a conduction-cooled BSCCO current lead

Description: A one-dimensional heat conduction model is employed to predict burnout of a Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} current lead. The upper end of the lead is assumed to be at 77 K and the lower end is at 4 K. The results show that burnout always occurs at the warmer end of the lead. The lead reaches its burnout temperature in two distinct stage. Initially, the temperature rises slowly when part of the lead is in flux-flow state. As the local temperature reaches the critical temperature, it begins to increase sharply. Burnout time depends strongly on flux-flow resistivity.
Date: October 1996
Creator: Seol, S. Y.; Cha, Y. S.; Niemann, R. C. & Hull, J. R.
Partner: UNT Libraries Government Documents Department

Flux-flow resistivity of three high-temperature superconductors

Description: Results of experiments on flux-flow resistivity (the relationship of voltage to current) of three high-temperature superconductors are described. The superconductors are a melt-cast BSCCO 2212 rod, a single filament BSCCO powder-in-tube (PIT) tape, and a multifilament PIT tape. The flux-flow resistivity of these superconductors was measured at three temperatures: 77 K (saturated liquid nitrogen), 87 K (saturated liquid argon), and 67 K (subcooled liquid nitrogen). Implications of the present results for practical applications are discussed.
Date: October 1996
Creator: Cha, Y. S.; Evans, D. J.; Hull, J. R. & Seol, S. Y.
Partner: UNT Libraries Government Documents Department

A Preliminary Study of Energy Recovery in Vehicles by Using Regenerative Magnetic Shock Absorbers

Description: Road vehicles can expend a significant amount of energy in undesirable vertical motions that are induced by road bumps, and much of that is dissipated in conventional shock absorbers as they dampen the vertical motions. Presented in this paper are some of the results of a study aimed at determining the effectiveness of efficiently transforming that energy into electrical power by using optimally designed regenerative electromagnetic shock absorbers. In turn, the electrical power can be used to recharge batteries or other efficient energy storage devices (e.g., flywheels) rather than be dissipated. The results of the study are encouraging - they suggest that a significant amount of the vertical motion energy can be recovered and stored.
Date: May 14, 2001
Creator: Goldner, R. B.; Zerigian, P. & Hull, J. R.
Partner: UNT Libraries Government Documents Department

Critical heat flux and boiling heat transfer to water in a 3-mm-diameter horizontal tube.

Description: Boiling of the coolant in an engine, by design or by circumstance, is limited by the critical heat flux phenomenon. As a first step in providing relevant engine design information, this study experimentally addressed both rate of boiling heat transfer and conditions at the critical point of water in a horizontal tube of 2.98 mm inside diameter and 0.9144 m heated length. Experiments were performed at system pressure of 203 kPa, mass fluxes in range of 50 to 200 kg/m{sup z}s, and inlet temperatures in range of ambient to 80 C. Experimental results and comparisons with predictive correlations are presented.
Date: December 4, 2000
Creator: Yu, W.; Wambsganss, M. W.; Hull, J. R. & France, D. M.
Partner: UNT Libraries Government Documents Department

Factors affecting characterization of bulk high-temperature superconductors

Description: Three major factors affect the characterization of bulk high-temperature superconductors in terms of their levitation properties during interaction with permanent magnets. First, the appropriate parameter for the permanent magnet is internal magnetization, not the value of the magnetic field measured at the magnet`s surface. Second, although levitation force grows with superconductor thickness and surface area, for a given permanent magnet size, comparison of levitation force between samples is meaningful when minimum values are assigned to the superconductor size parameters. Finally, the effect of force creep must be considered when time-averaging the force measurements. In addition to levitational force, the coefficient of friction of a levitated rotating permanent magnet may be used to characterize the superconductor.
Date: November 1, 1997
Creator: Hull, J.R.
Partner: UNT Libraries Government Documents Department

Depinning of flux lines and AC losses in magnet-superconductor levitation system

Description: The AC loss characteristics of a magnet-superconductor system were studied with the magnet fixed to the free end of an oscillating cantilever located near a stationary melt-textured YBCO pellet. Below a threshold AC field amplitude {approx}2Oe, the dissipation of the oscillator is amplitude-independent, characteristic of a linear, non-hysteretic regime. Above threshold,dissipation increases with amplitude, reflecting the depinning and hysteretic motion of flux lines. The threshold AC field is an order of magnitude higher than that measured for the same YBCO material via AC susceptometry in a uniform DC magnetic field, A partial lock-in of flux lines between YBCO ab planes is proposed as the mechanism for the substantial increase of the depinning threshold.
Date: November 29, 1999
Creator: Terentiev, A. N.; Hull, J. R. & De Long, L. E.
Partner: UNT Libraries Government Documents Department

Fault current limiter-predominantly resistive behavior of a BSCCO shielded-core reactor

Description: Tests were conducted to determine the electrical and magnetic characteristics of a superconductor shielded core reactor (SSCR). The results show that a closed-core SSCR is predominantly a resistive device and an open-core SSCR is a hybrid resistive/inductive device. The open-core SSCR appears to dissipate less than the closed-core SSCR. However, the impedance of the open-core SSCR is less than that of the closed-core SSCR. Magnetic and thermal diffusion are believed to be the mechanism that facilitates the penetration of the superconductor tube under fault conditions.
Date: June 30, 2000
Creator: Ennis, M. G.; Tobin, T. J.; Cha, Y. S. & Hull, J. R.
Partner: UNT Libraries Government Documents Department

Conceptual design of a forced-flow-cooled 20-kA current lead using Ag-alloy-sheathed Bi-2223 high-temperature superconductors

Description: The use of high-temperature superconductors in current leads to reduce refrigeration power has been investigated by many groups in the past. Most used YBCO and Bi-2212 bulk superconductors, although their critical current density is not very high. In this paper, BI-2223 HTSC tapes sheathed with Ag alloys are used in the design of a 20-kA current lead because of their higher critical current in medium magnetic fields. The lead current of 20 kA is related to the coil current of the planned stellarator WENDELSTEIN 7-X. Forced-now helium cooling has been used in the design, allowing position-independent and well-controlled operation. The design characteristics of the lead are presented and 4-K helium cooling of the whole lead, as well as 60-K helium cooling of the copper part of the lead, is discussed. The power consumption at zero current, and the lead`s behaviour in case of loss of coolant flow, are given, The results of the design allow extrapolation to current leads of the 50-kA range.
Date: November 1, 1994
Creator: Heller, R. & Hull, J.R.
Partner: UNT Libraries Government Documents Department

Computer modeling of electromagnetic fields and fluid flows for edge containment in continuous casting

Description: A computer model was developed to predict eddy currents and fluid flows in molten steel. The model was verified by comparing predictions with experimental results of liquid-metal containment and fluid flow in electromagnetic (EM) edge dams (EMDs) designed at Inland Steel for twin-roll casting. The model can optimize the EMD design so it is suitable for application, and minimize expensive, time-consuming full-scale testing. Numerical simulation was performed by coupling a three-dimensional (3-D) finite-element EM code (ELEKTRA) and a 3-D finite-difference fluids code (CaPS-EM) to solve heat transfer, fluid flow, and turbulence transport in a casting process that involves EM fields. ELEKTRA is able to predict the eddy- current distribution and the electromagnetic forces in complex geometries. CaPS-EM is capable of modeling fluid flows with free surfaces. Results of the numerical simulation compared well with measurements obtained from a static test.
Date: February 1, 1996
Creator: Chang, F.C.; Hull, J.R.; Wang, Y.H. & Blazek, K.E.
Partner: UNT Libraries Government Documents Department

Design, Construction, and Initial Operation of the ANL Research Salt-Gradient Solar Pond

Description: The design consideration of a 1/4 acre research salt-gradient solar pond is described. Experience learned during the construction of the solar pond is presented. Initial operation of the pond indicates that the construction of the pond is sound and no leakage has occurred. The pond began to warm up during March of 1981. The maximum pond temperature reached 63 C at the end of July and it is still rising. All signs indicate that the operation of the well instrumented pond will be a success and the performance of the pond will be as expected, if not better.
Date: 1981
Creator: Cha, Y. S.; Sha, W. T. & Hull, J. R.
Partner: UNT Libraries Government Documents Department