skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Transient magnetic field and temperature modeling in large magnet applications

Abstract

This paper discusses a coupled magnetic/thermal model developed to study heat and magnetic field diffusion in conducting materials subject to time-varying external fields. There are numerous applications, both military and commercial. These include: energy storage devices, pulsed power transformers, and electromagnetic launchers. The time scales of interest may range from a magnetic field pulse of a microsecond in an electromagnetic launcher, to hundreds of seconds in an energy storage magnet. The problem can be dominated by either the magnetic field or heat diffusion, depending on the temperature and the material properties of the conductor. In general, heat diffuses much more rapidly in high electrical conductivity materials of cryogenic temperatures. The magnetic field takes longer to diffuse, since screening currents can be rapidly set up which shield the interior of the material from further magnetic field penetration. Conversely, in high resistivity materials, the magnetic field diffuses much more rapidly. A coupled two-dimensional thermal/magnetic model has been developed. The results of this model, showing the time and spatial variation of the magnetic field and temperature, are discussed for the projectile of an electromagnetic launcher.

Authors:
; ; ;  [1]
  1. (General Dynamics Corp., San Diego, CA (USA). Space Systems Div.)
Publication Date:
OSTI Identifier:
5272380
Resource Type:
Journal Article
Resource Relation:
Journal Name: IEEE (Institute of Electrical and Electronics Engineers) Transactions on Magnetics; (USA); Journal Volume: 25:4
Country of Publication:
United States
Language:
English
Subject:
25 ENERGY STORAGE; MAGNETIC ENERGY STORAGE; TRANSFORMERS; MAGNETS; ELECTRIC CONDUCTIVITY; CRYOGENICS; ELECTRIC CONDUCTORS; HEAT TRANSFER; LAUNCHING; MAGNETIC FIELDS; MAGNETIC SHIELDING; PROJECTILES; ELECTRICAL EQUIPMENT; ELECTRICAL PROPERTIES; ENERGY STORAGE; ENERGY TRANSFER; EQUIPMENT; PHYSICAL PROPERTIES; SHIELDING; STORAGE; 250100* - Energy Storage- Magnetic

Citation Formats

Gurol, H., Hardy, G.E., Peck, S.D., and Leung, E. Transient magnetic field and temperature modeling in large magnet applications. United States: N. p., 1989. Web. doi:10.1109/20.34304.
Gurol, H., Hardy, G.E., Peck, S.D., & Leung, E. Transient magnetic field and temperature modeling in large magnet applications. United States. doi:10.1109/20.34304.
Gurol, H., Hardy, G.E., Peck, S.D., and Leung, E. Sat . "Transient magnetic field and temperature modeling in large magnet applications". United States. doi:10.1109/20.34304.
@article{osti_5272380,
title = {Transient magnetic field and temperature modeling in large magnet applications},
author = {Gurol, H. and Hardy, G.E. and Peck, S.D. and Leung, E.},
abstractNote = {This paper discusses a coupled magnetic/thermal model developed to study heat and magnetic field diffusion in conducting materials subject to time-varying external fields. There are numerous applications, both military and commercial. These include: energy storage devices, pulsed power transformers, and electromagnetic launchers. The time scales of interest may range from a magnetic field pulse of a microsecond in an electromagnetic launcher, to hundreds of seconds in an energy storage magnet. The problem can be dominated by either the magnetic field or heat diffusion, depending on the temperature and the material properties of the conductor. In general, heat diffuses much more rapidly in high electrical conductivity materials of cryogenic temperatures. The magnetic field takes longer to diffuse, since screening currents can be rapidly set up which shield the interior of the material from further magnetic field penetration. Conversely, in high resistivity materials, the magnetic field diffuses much more rapidly. A coupled two-dimensional thermal/magnetic model has been developed. The results of this model, showing the time and spatial variation of the magnetic field and temperature, are discussed for the projectile of an electromagnetic launcher.},
doi = {10.1109/20.34304},
journal = {IEEE (Institute of Electrical and Electronics Engineers) Transactions on Magnetics; (USA)},
number = ,
volume = 25:4,
place = {United States},
year = {Sat Jul 01 00:00:00 EDT 1989},
month = {Sat Jul 01 00:00:00 EDT 1989}
}
  • We present the designs of probes for making critical current density (J{sub c}) measurements on anisotropic high-temperature superconducting tapes as a function of field, field orientation, temperature and strain in our 40 mm bore, split-pair 15 T horizontal magnet. Emphasis is placed on the design of three components: the vapour-cooled current leads, the variable temperature enclosure, and the springboard-shaped bending beam sample holder. The vapour-cooled brass critical-current leads used superconducting tapes and in operation ran hot with a duty cycle (D) of ∼0.2. This work provides formulae for optimising cryogenic consumption and calculating cryogenic boil-off, associated with current leads usedmore » to make J{sub c} measurements, made by uniformly ramping the current up to a maximum current (I{sub max}) and then reducing the current very quickly to zero. They include consideration of the effects of duty cycle, static helium boil-off from the magnet and Dewar (b{sup ′}), and the maximum safe temperature for the critical-current leads (T{sub max}). Our optimized critical-current leads have a boil-off that is about 30% less than leads optimized for magnet operation at the same maximum current. Numerical calculations show that the optimum cross-sectional area (A) for each current lead can be parameterized by LI{sub max}/A=[1.46D{sup −0.18}L{sup 0.4}(T{sub max}−300){sup 0.25D{sup −{sup 0{sup .{sup 0{sup 9}}}}}}+750(b{sup ′}/I{sub max})D{sup 10{sup −{sup 3I{sub m}{sub a}{sub x}−2.87b{sup ′}}}}]× 10{sup 6}A m{sup −1} where L is the current lead's length and the current lead is operated in liquid helium. An optimum A of 132 mm{sup 2} is obtained when I{sub max} = 1000 A, T{sub max} = 400 K, D = 0.2, b{sup ′} = 0.3 l h{sup −1} and L = 1.0 m. The optimized helium consumption was found to be 0.7 l h{sup −1}. When the static boil-off is small, optimized leads have a boil-off that can be roughly parameterized by: b/I{sub max } ≈ (1.35 × 10{sup −3})D{sup 0.41} l h{sup ‑1} A{sup −1}. A split-current-lead design is employed to minimize the rotation of the probes during the high current measurements in our high-field horizontal magnet. The variable-temperature system is based on the use of an inverted insulating cup that operates above 4.2 K in liquid helium and above 77.4 K in liquid nitrogen, with a stability of ±80 mK to ±150 mK. Uniaxial strains of −1.4% to 1.0% can be applied to the sample, with a total uncertainty of better than ±0.02%, using a modified bending beam apparatus which includes a copper beryllium springboard-shaped sample holder.« less
  • The superconducting magnet systems of future fusion reactors, such as a Demonstration Power Plant (DEMO), will produce magnetic field energies in the 10 s of GJ range. The release of this energy during a fault condition could produce arcs that can damage the magnets of these systems. The public safety consequences of such events must be explored for a DEMO reactor because the magnets are located near the DEMO's primary radioactive confinement barrier, the reactor's vacuum vessel (VV). Great care will be taken in the design of DEMO's magnet systems to detect and provide a rapid field energy dump tomore » avoid any accidents conditions. During an event when a fault condition proceeds undetected, the potential of producing melting of the magnet exists. If molten material from the magnet impinges on the walls of the VV, these walls could fail, resulting in a pathway for release of radioactive material from the VV. A model is under development at Idaho National Laboratory (INL) called MAGARC to investigate the consequences of this accident in a large toroidal field (TF) coil. Recent improvements to this model are described in this paper, along with predictions for a DEMO relevant event in a toroidal field magnet.« less
  • A magnetic field drift, gradual decrease of the order of 10{sup -4} in several tens of hours, was observed with the beam intensity decrease in an operation of an azimuthally varying field (AVF) cyclotron. From our experimental results, we show that the temperature increase of the magnet iron by the heat transfer from the excitation coils can induce such change of the magnetic field as to deteriorate the beam quality. The temperature control of the magnet iron was realized by thermal isolation between the main coil and the yoke and by precise control of the cooling water temperature of themore » trim coils attached to the pole surfaces in order to prevent temperature change of the magnet iron. The magnetic field stability of {+-}5x10{sup -6} and the beam intensity stability of {+-}2% have been achieved by this temperature control.« less
  • This paper presents the theoretical and experimental studies of a dual-magnet (DM) configuration that forms the electromagnetic circuit of a nanopositioning actuator. Motivation of this work arises when an accurate prediction of the magnetic field behavior within the DM configuration is required to achieve ultrahigh precision motion control. In the theoretical modeling, the DM configuration is decomposed into several regions where each region is treated as a boundary-value problem. A method, termed superposition of the boundary conditions, is used to obtain the field solution of an air gap that is influenced by two magnetic sources. Consequently, a two-dimensional (2D) analyticalmore » model that accurately predicts the magnetic field behavior of the DM configuration is presented. In the experimental investigations, the magnetic flux density measured from a DM configuration prototype is used to validate the accuracy of the 2D analytical model. These experimental data were also compared against the magnetic flux density collected from a conventional single-magnet configuration prototype. Such comparisons verify the claimed features of the DM configuration, i.e., providing 40% increase in the magnetic flux density and offering an evenly distributed magnetic field through the entire air gap of 11 mm.« less