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Conceptual design of a 20-MJ superconducting forced cooled ohmic-heating coil

Description: Conceptual design of a 20 MJ superconducting coil is described which was developed to demonstrate the feasibility of an ohmic-heating system. The superconductor material was Nb/sub 3/Sn for a 9 tesla maximum field. Cabled and braided conductors were investigated and the braided conductors were identified as the best alternates due to their high operating current densities and because of its porosity. The coil was designed to be cryostable for bipolar operation from +9 tesla to -9 tesla maximum field within 1 second. The forced cooled design utilizes cross flow cooling. The coil was designed to generate the flux swing while simultaneously meeting the limitations imposed by cooling, insulation, current density and stresses in the materials.
Date: January 1, 1978
Creator: Singh, S.K.; Murphy, J.H.; Janocko, M.A.; Haller, H.E.; Litz, D.C.; Eckels, P.W. et al.
Partner: UNT Libraries Government Documents Department

Magnetic refrigeration: the promise and the problems

Description: Magnetic refrigeration uses the temperature- and field-dependence of the entropy of some magnetic materials to accomplish cooling. Because of the intrinsically high efficiency of the magnetization and demagnetization process and because of the potential for excellent heat transfer between solids and fluids, magnetic refrigerators promise to have higher efficiency than existing gas-cycle refrigerators. Many ground-based and space-based applications could benefit significantly from the cost savings implied by higher efficiency. Other attributes of these devices are high reliability and low volume and mass per unit cooling power. The development of these refrigerators is underway at several places around the world, including the Los Alamos National Laboratory. The progress to date has been encouraging but some problems have been clearly identified. The arguments for high efficiency and the problems that will need to be solved to achieve this goal are discussed.
Date: January 1, 1984
Creator: Barclay, J.A.
Partner: UNT Libraries Government Documents Department

Improvements in the weldability of a superconductor sheath material

Description: This paper investigates the effects of chemistry and heat treatment variation on the 4-K tensile properties of A-286, a candidate sheath material for force-cooled superconductors. Currently, full use of A-286 and similar superalloys is limited by the observed low yield and ultimate tensile strengths in the welded and aged condition. The low strength is shown to be associated with the formation of precipitate-free zones as a result of alloying-element segregation during weld pool solidification. It has been determined that minor modifications of the weld-metal chemistry by the addition of Ti reduce precipitate-free-zone formation, resulting in matching weld-metal and base-plate strengths at 4 K. Furthermore, nucleation of the ..gamma..' hardening phase has been found to be a strong function of temperature and composition. Modified heat-treatment schedules have been determined that are amenable to superconductor fabrication and that resulted in increased weld hardening and improved 4-K tensile properties.
Date: August 7, 1985
Creator: Summers, L.T. & Morris, J.W. Jr.
Partner: UNT Libraries Government Documents Department

Simulation program for central helium liquefier

Description: The computer program described here analyzes the performance of Fermilab Central Helium Liquefier (CHL) and predicts the values of the plant thermodynamic variables at all process points in the plant. To simulate CHL, this program is modified from the prototype program which was developed by Hitachi Ltd. a couple of years ago. This program takes care of only the steady state simulation and takes account of the change of the turbine efficiency, the pressure drops and the UA values of the heat exchangers. How to use the program is shown.
Date: February 20, 1984
Creator: Kawamura, S.
Partner: UNT Libraries Government Documents Department

Superconductor development program at Lawrence Livermore Laboratory

Description: Winding of a Nb--Ti test coil at the Lawrence Livermore Laboratory is nearly complete. The conductor in this coil operates in a maximum field of 7.5 T and provides the 2-T field required by the Mirror Fusion Test Facility. Nb/sub 3/Sn multifilamentary conductors, made using the ''bronze'' technique, appear capable of providing the higher fields needed by commercial reactors.
Date: January 19, 1978
Creator: Cornish, D.N.
Partner: UNT Libraries Government Documents Department

Reliability of large superconducting magnets through design

Description: As superconducting magnet systems grow larger and become the central component of major systems involving fusion, magnetohydrodynamics, and high-energy physics, their reliability must be commensurate with the enormous capital investment in the projects. Although the magnet may represent only 15% of the cost of a large system such as the Mirror Fusion Test Facility, its failure would be catastrophic to the entire investment. Effective quality control during construction is one method of ensuring success. However, if the design is unforgiving, even an inordinate amount of effort expended on quality control may be inadequate. Creative design is the most effective way of ensuring magnet reliability and providing a reasonable limit on the amount of quality control needed. For example, by subjecting the last drawing operation is superconductor manufacture to a stress larger than the magnet design stress, a 100% proof test is achieved; cabled conductors offer mechanical redundancy, as do some methods of conductor joining; ground-plane insulation should be multilayered to prevent arcs, and interturn and interlayer insulation spaced to be compatible with the self-extinguishing of arcs during quench voltages; electrical leads should be thermally protected; and guard vacuum spaces can be incorporated to control helium leaks. Many reliable design options are known to magnet designers. These options need to be documented and organized to produce a design guide. Eventually, standard procedures, safety factors, and design codes can lead to reliability in magnets comparable to that obtained in pressure vessels and other structures. Wihout such reliability, large-scale applications in major systems employing magnetic fusion energy, magnetohydrodynamics, or high-energy physics would present unacceptable economic risks.
Date: September 5, 1980
Creator: Henning, C.D.
Partner: UNT Libraries Government Documents Department

Performance testing of a commercially produced cryogenic refrigerator

Description: A commercially available cryogenic refrigeration unit, model M-20, (3-phase, 60-Hz, 230-V) manufactured by Cryodynamics, Inc., was subjected to laboratory testing to measure some of its performance characteristics. Comparisons were made with those performance characteristics given in manufacturer literature for the M-20 unit (3-phase, 400-Hz, 208-V). At 77 K, the measured cooling capacity of the 60-Hz/230-V unit was very nearly the same (<2% difference) as the specified capacity (110 W) of the 400-Hz/208-V unit. At temperature levels higher than 77 K, measured cooling capacities exceeded the manufacturer product data sheet values. Coefficients of performance (COP) based on the experimental measurements ranged from about 0.37 at 250 K to 0.03 at 70 K. Comparison of measured to ideal (Carnot cycle) COPs yielded values ranging from about 8 to 18%, with broad maximum occurring between approximately 100 and 150 K. Finally, the measured cool-down time from room temperature to 77 K was about 10 minutes compared with a specification sheet value of 7.4 minutes. This difference may be attributed to lower thermal mass (without heater block) and higher operating frequency conditions associated with the specification. 6 figs., 2 tabs.
Date: September 1, 1990
Creator: Keshock, E.G. (Tennessee Univ., Knoxville, TN (USA). Dept. of Mechanical and Aerospace Engineering) & Murphy, R.W. (Oak Ridge National Lab., TN (USA))
Partner: UNT Libraries Government Documents Department

Analysis of magnetic refrigerators with external regeneration

Description: The central idea of the magnetic refrigeration systems analyzed in this paper is that of a MR having a regenerator composed of an integral number of separate stages but having only a single magnetic stage. In principle, each stage is thermally isolated from the others, but the stages are accessed by a manifold and valve system which allows gas to flow between the MM and the individual stages. The concept therefore is distinctly unlike that of the unusual continuous regenerator of gas refrigerators. Although a small amount of gas in the manifold is responsible for the actual transfer of heat between elements of the REGMR, it is clear from the cycle description in the caption of Fig. 1 that the fixed mass of the MM is analogous to a fixed mass of a working fluid in a gas refrigerator or engine. Both, in effect, are carried thermally through all parts of their respective systems.
Date: January 1, 1986
Creator: Overton, W.C. Jr. & Barclay, J.A.
Partner: UNT Libraries Government Documents Department

Evaluation and design of a large spacing loop-loop electromagnetic tool

Description: This paper investigates the potential use of a large spacing loop-loop electromagnetic logging tool to detect resistivity anomalies as far as 25 meters away from the borehole wall. A three-dimensional whole space electromagnetic modelling code was used to evaluate the response of such a tool to various transmitter and receiver loop orientations, operating frequencies, loop spacings, resistivity contrasts, anomaly sizes and anomaly distances. Anomalies were modeled as finite extent sheets of various thicknesses which terminated before intersecting the borehole wall. It was found that both coplanar and coaxial loop orientations provide strong anomaly response, but the coaxial loop orientation has superior depth penetration and is a less complex tool to design and build. For such a coaxial tool, anomalies could be detected as far from the borehole wall as half the loop spacing. For rock resistivities on the order of 100 ohm-m, contrasts greater than 2:1 and loop spacings of 75 meters the optimal operating frequency is shown to be 10 kHz. At these loop spacings, anomalies must be thicker 10 meters to be detected. It is further shown that for coaxial loops the nature of the response curves allows one to estimate the distance of an anomaly from the borehole wall although no angular location is possible. A coaxial loop-loop electromagnetic tool design that is currently being built is presented. This tool provides for a downhole power supply to a transmitter loop with a magnetic moment between 100 and 1000 A/m/sup 2/ that is electrically isolated via a fiber optic link from the variably spaced receiver located above. Signal detection is provided by a high sensitivity lock-in amplifier. The errors are conservatively estimated for this design at 5%. Thus anomalies resulting in a secondary field less than 5% of the primary transmitted field are deemed undetactable. 11 figs.
Date: February 1, 1986
Creator: Harben, P.E.; Rodgers, P.W. & Holladay, G.
Partner: UNT Libraries Government Documents Department

Support-electrode torque on a spherical superconducting gyroscope

Description: In 1960, L.I. Schiff observed that precise measurement of the precession of a spherical gyroscope orbiting the earth could provide a test of general relativity. The current effort to implement this experiment was initiated shortly thereafter by W.M. Fairbank. The gyroscope will be a fused-quartz sphere coated with superconductive niobium. The spinning superconducting coating generates a small magnetic field (the London field) which outside the rotor is that of a magnetic dipole and inside is uniform and parallel to the spin axis. The magnetic flux that this field produces in superconducting loops encompassing the rotor will change as the gyroscope precesses; the precession of the gyroscope will be measured by measuring the change in flux. Because the anticipated relativistic precession is extremely small, it is essential that no significant torques be coupled to the gyroscope through its London field. The torque on a superconducting sphere rotating in an arbitrary magnetic field can be expressed in terms of the l = 1 coefficients of the expansion of the field in spherical harmonic functions. In general, a boundary-value problem must be solved in order to obtain these coefficients. The diamagnetic torque produced by superconducting support electrodes is calculated. (WHK)
Date: January 1, 1982
Creator: Holdeman, L.B. & Holdeman, J.T. Jr.
Partner: UNT Libraries Government Documents Department

Experiment to determine properties of packed particle beds and regenerators at cryogenic temperatures

Description: The testing of the properties of packed-particle beds and regenerators at cryogenic temperatures as low as 4 K is an essential part of the magnetic refrigeration research and development program at the Los Alamos National Laboratory. We envision magnetic refrigeration and heat pump systems operating in various ranges from 4 K to ambient temperature and above. Only pressurized helium gas appears suitable as the heat exchange fluid for the low-temperature applications. Because published data on the properties of porous beds at low temperatures is sparse, we have found it necessary to develop an experimental test apparatus to study the properties of various configurations of beds and regenerators. Two of the well-known methods for such studies are the steady-enthalpy-flux method and the single-blow transient method. We have developed an experimental system in which gas flow can be suddenly switched to an alternate better (or colder) flow in step-function fashion at temperatures from 4 to 300 K. This apparatus will yield information on steady-state heat transfer and friction factors as well as on the transient behavior. Such information is very important to the design of high-efficiency magnetic refrigeration systems. This paper describes this experimental apparatus and presents the results and analysis of recent measurements on packed-particle beds in the liquid helium and liquid nitrogen temperature ranges.
Date: January 1, 1983
Creator: Barclay, J.A.; Overton, W.C. Jr.; Stewart, W.F. & Sarangi, S.
Partner: UNT Libraries Government Documents Department

Lansce liquid hydrogen moderator system hardware-characteristic-operation

Description: In this paper, we report the current status of the hardware development and testing program for a liquid hydrogen moderator system currently being fabricated for installation into the Los Alamos Neutron Scattering Center (LANSCE) upgraded target system.
Date: January 1, 1985
Creator: Robinson, H.; Russell, G.J.; Tucker, E.; Whitaker, R.; Williamson, K. & Edeskuty, F.
Partner: UNT Libraries Government Documents Department

Superconducting fault-current limiter and inductor design

Description: A superconducting fault current limiter (SFCL) that uses a biased superconducting inductor in a diode or thyristor bridge circuit was analyzed for transmission systems in 69, 138, and 230 rms kV utility transmission systems. The limiter was evaluated for costs with all components - superconducting coil, diode and/or SCR power electronics, high voltage insulation, high voltage bushings and vapor cooled leads, dewar, and refrigerator - included. A design was undertaken for the superconducting cable and coils for both diode and SCR 69 kV limiter circuits.
Date: January 1, 1982
Creator: Rogers, J.D.; Boenig, H.J.; Chowdhuri, P.; Schermer, R.I.; Wollan, J.J. & Weldon, D.M.
Partner: UNT Libraries Government Documents Department

Field enhancement of a 12. 5-T magnet using holmium poles

Description: Unlike conventional ferromagnetic materials such as iron and Supermendur, which produce saturation magnetization fields of approximately 2 T, several of the rare-earth elements (holmium, terbium, erbium, gadolinium, and dysprosium) yield saturated fields of nearly 4 T. This property makes these rare-earth metals particularly attractive as flux concentrators for use in superconducting magnets. This report concerns the use of holmium inserts to enhance the peak useful field of the nominally 12.5-T, 5-cm-bore tape magnet manufactured by the Intermagnetics General Corporation (IGC). Nonlinear magnetostatic analysis indicates that this field increases to nearly 16 T with the rare-earth poles inserted within the bore on both sides of the coil's split-plane radial access gap. This paper focuses on computer modeling methods and experimental results.
Date: September 7, 1984
Creator: Hoard, R.W.; Mance, S.C.; Leber, R.L.; Dalder, E.N.; Chaplin, M.R.; Blair, K. et al.
Partner: UNT Libraries Government Documents Department

Magnetic refrigeration for spacecraft systems

Description: Magnetic refrigerators, i.e., those that use the magnetocaloric effect of a magnetic working material in a thermodynamic cycle, offer potentially reliable, and efficient refrigeration over a variety of temperature ranges and cooling powers. A descriptive analysis of magnetic refrigeration systems is performed with particular emphasis on more efficient infrared detector cooling. Three types of magnetic refrigerator designs are introduced to illustrate some of the possibilities.
Date: January 1, 1981
Creator: Barclay, J.A.
Partner: UNT Libraries Government Documents Department

The high T/sub c/ superconducting bolometer

Description: A description is given of the optimization of a bolometric infrared detector which uses the resistive transition of a high T/sub c/ film as the thermometer. The performance of a LN cooled far infrared bolometer operated with a cooled low-pass filter is computed for the ideal case of a noise-free readout. The theory is then extended to include various contributions to the readout noise. Measurements are presented of the low frequency noise near T/sub c/ in current biased films of ErBa/sub 2/Cu/sub 3/O/sub 7/, which show that useful performance can be achieved. Comparisons are made with other infrared detection technologies which show that practical high T/sub c/ bolometers will be especially useful for wavelengths longer than the /approximately/20 ..mu..m cutoff of LN cooled photovoltaic detectors. Potential applications include far infrared laboratory spectroscopy and passively cooled space observations of bright sources such as the earth. 6 refs., 3 figs.
Date: August 1, 1988
Creator: Richards, P.L.; Verghese, S.; Geballe, T.H. & Spielman, S.R.
Partner: UNT Libraries Government Documents Department

Superconducting transistor

Description: A three film superconducting tunneling device, analogous to a semiconductor transistor, is presented, including a theoretical description and experimental results showing a current gain of four. Much larger current gains are shown to be feasible. Such a development is particularly interesting because of its novelty and the striking analogies with the semiconductor junction transistor.
Date: January 1, 1978
Creator: Gray, K. E.
Partner: UNT Libraries Government Documents Department

Program NICOLET to integrate energy loss in superconducting coils. [In FORTRAN for CDC-6600]

Description: A voltage pickup coil, inductively coupled to the magnetic field of the superconducting coil under test, is connected so its output may be compared with the terminal voltage of the coil under test. The integrated voltage difference is indicative of the resistive volt-seconds. When multiplied with the main coil current, the volt-seconds yield the loss. In other words, a hysteresis loop is obtained if the integrated voltage difference phi = ..integral delta..Vdt is plotted as a function of the coil current, i. First, time functions of the two signals phi(t) and i(t) are recorded on a dual-trace digital oscilloscope, and these signals are then recorded on magnetic tape. On a CDC-6600, the recorded information is decoded and plotted, and the hysteresis loops are integrated by the set of FORTRAN programs NICOLET described in this report. 4 figures.
Date: August 1, 1978
Creator: Vogel, H.F.
Partner: UNT Libraries Government Documents Department

A comparison of the conductor requirements for energy storage devices made with ideal coil geometries

Description: Superconducting Magnetic Energy Storage (SMES) plants have been proposed in both solenoidal and toroidal geometries. The former is efficient in terms of the quantity of superconductor required per unit of stored energy. For applications where a fringe field could be a problem, the toroidal geometry, which requires at least a factor of two more material, has been proposed. In addition to the solenoid and toroid, other geometries are possible, such as linear multipoles and spherical coils. These geometries have been considered for use in applications other than energy storage. In this report, the effectiveness (quantity of superconductor/stored energy) is calculated for various coil geometries. 7 refs., 4 tabs.
Date: August 1, 1988
Creator: Hassenzahl, W.
Partner: UNT Libraries Government Documents Department

Vacuum impregnation with epoxy of large superconducting magnet structures

Description: The Lawrence Berkeley Laboratory (LBL) has been developing a new generation of superconducting magnets which have the helium cooling system as an integral part of the magnet structure. The LBL technique calls for large sections of the magnet structure to be vacuum impregnated with epoxy. The epoxy was chosen for its impregnation properties. Epoxies which have good impregnation characteristics are often subject to cracking when they are cooled to cryogenic temperatures. The cracking of such an epoxy can be controlled by: (1) minimizing the amount of epoxy in the structure; (2) reducing the size of unfilled epoxy spaces; and (3) keeping the epoxy in compression. The technique for using the epoxy is often more important than the formulation of the epoxy. The LBL vacuum impregnation and curing technique is described. Experimental measurements on small samples of coil sections are presented. Practical experience with large vacuum impregnation superconducting coils (up to two meters in dia) is also discussed.
Date: June 1, 1978
Creator: Green, M.A.; Coyle, D.E.; Miller, P.B. & Wenzel, W.F.
Partner: UNT Libraries Government Documents Department

Problem of evaluating the safety of an explosive

Description: Some general considerations on the problem of evaluating the safety of an explosive lead to the reasons why the much-criticized drop-weight impact machine remains an important tool in most explosive research and development laboratories. Problems related to the design, calibration, and use of such machines, and certain misconceptions concerning the interpretation of the test data, are discussed. The results of an unsuccessful attempt to construct a more comprehensive hazards scale also are described.
Date: January 1, 1977
Creator: Smith, L. C.
Partner: UNT Libraries Government Documents Department