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EP1018126A2 - Bobine supraconductrice a caracteristique q elevee et a faibles pertes - Google Patents

Bobine supraconductrice a caracteristique q elevee et a faibles pertes

Info

Publication number
EP1018126A2
EP1018126A2 EP97906900A EP97906900A EP1018126A2 EP 1018126 A2 EP1018126 A2 EP 1018126A2 EP 97906900 A EP97906900 A EP 97906900A EP 97906900 A EP97906900 A EP 97906900A EP 1018126 A2 EP1018126 A2 EP 1018126A2
Authority
EP
European Patent Office
Prior art keywords
coil
superconducting
superconductor
tape
superconducting magnetic
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP97906900A
Other languages
German (de)
English (en)
Other versions
EP1018126A4 (fr
Inventor
Bruce B. Gamble
Gregory L. Snitchler
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
American Superconductor Corp
Original Assignee
American Superconductor Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by American Superconductor Corp filed Critical American Superconductor Corp
Publication of EP1018126A2 publication Critical patent/EP1018126A2/fr
Publication of EP1018126A4 publication Critical patent/EP1018126A4/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F6/00—Superconducting magnets; Superconducting coils
    • H01F6/06—Coils, e.g. winding, insulating, terminating or casing arrangements therefor

Definitions

  • the invention relates to superconducting magnetic coils.
  • Q is defined as the ratio of the stored inductive energy with respect to the dissipation of the coil per cycle.
  • the very best copper or copper-iron wound inductive coils have Qs reaching 200.
  • Inductive coils have been fabricated using bulk ceramic superconducting materials. Because such bulk materials do not include a surrounding matrix-forming material, losses associated with eddy currents are minimized, making the materials attractive for use in high Q coils. However, there are problems associated with building high Q coils from such materials. Such ceramic materials normally have relatively high resistance characteristics in their normal state. Thus, if the ceramic were to lose its superconductivity characteristic (e.g., due to loss of cooling) and revert to its normal state, the stored energy in the coil would dissipate very quickly as heat in the coil. Because the ceramic material of the coil itself must dissipate the heat, the coil may, in many cases, overheat, causing irreversible damage (e.g., cracking) to the coil. Summary of the Invention
  • a superconducting magnetic coil for generating a magnetic field that varies along longitudinal and radial axes of the coil includes a superconductor tape wound about the longitudinal axis of the coil.
  • the superconductor tape includes a multi- filament composite superconductor having individual filaments surrounded or supported by a matrix-forming material.
  • the superconducting coil has a Q characteristic greater than 250 at a frequency less than 1,000 Hz, with the Q defined as the ratio of the stored inductive energy in the coil to the dissipation of the coil per cycle.
  • the superconductor tape is wound about itself, thereby forming a single-width, spirally-wound superconducting magnetic coil.
  • the superconducting magnetic coil can include a plurality of parallel-wound superconductor tapes each having the multi-filament composite superconductor.
  • the superconductor tape is formed of an anisotropic superconducting ceramic material (e.g. , copper oxide) .
  • the superconductor tape can be formed from a plurality of series-connected lengths of superconductor tapes. Each of the lengths can be connected to an adjoining length by a bridging segment, preferably formed of superconducting material.
  • the adjoining lengths can be spliced to each other.
  • the ratio of the diameter of the coil to the width of the superconducting tape of the single-layer coil is greater than 100.
  • the superconducting coil can have a diameter greater than one meter with the width of the superconductor tape forming said coil being less than 0.6 centimeters.
  • the superconducting magnetic coil can further include a plate member, formed of a ferromagnetic material (e.g., iron) and spaced a predetermined distance from one or both end regions of the superconducting coil.
  • the coil preferably has a Q characteristic greater than 250 at a frequency less than 200 Hz.
  • a method for fabricating a superconducting magnetic coil includes winding a superconductor tape, of the type and geometry described above, about the longitudinal axis of said coil in a single-width configuration.
  • a superconducting magnetic coil configuration and method of fabrication provides a coil with significantly reduced AC losses as well as an increased Q characteristic, for example, above 250 at frequencies less than 1,000 Hz, and preferably less than 200 Hz.
  • a superconducting coil with such a characteristic is invaluable as a key component in an efficient resonant circuit.
  • a single-width pancake coil configuration also has a significantly decreased effective width, thereby generating a field distribution with a much smaller radial field as compared to multi-pancake coil configurations.
  • more of the superconducting material lies along the radial axis (i.e., the axis defining the winding direction) rather than the longitudinal axis of the coil.
  • magnetic field analysis indicates the magnitude of the magnetic field is essentially zero at the center of the coil which further contributes to the overall reduction of the losses of the coil.
  • the filaments in the center of the superconducting tape experience almost no radial magnetic field; therefore, the tape is capable of carrying more current.
  • the magnetic field incident on the outer side edges of the tape is still far less than that experienced in multi-pancake coil stack configurations, such as in superconducting magnetic solenoids.
  • a further benefit of the single-width configuration is that the volume of superconducting material used to wind the coil is decreased, as compared to a conventional coil with similar magnetic field characteristic, thereby providing a further decrease in conduction losses.
  • the invention has particular advantages in those embodiments utilizing anisotropic superconducting compounds, such as multi-filament composite HTS superconductor having individual superconducting filaments surrounded by a matrix-forming material (e.g., silver).
  • a matrix-forming material e.g., silver
  • Fig. 1 is a perspective, partially cut-away, view of a superconducting magnetic coil in accordance with the invention.
  • Fig. IA is cross-sectional view of the superconducting magnetic coil taken along lines 1A-1A of Fig. 1.
  • Fig. 2 is a cross-sectional view of a multi ⁇ filament composite conductor.
  • Fig. 3 is a side view of the superconducting magnetic coil of Fig. 1.
  • Fig. 4 is a cross-sectional view of an alternative embodiment of a superconducting magnetic coil.
  • Fig. 5 is a side view of series-connected superconducting tapes wound two in hand.
  • Fig. 6 is a perspective view of a coil wound three in hand.
  • Coil assembly 10 includes a superconducting coil 12 wound in the form of a "pancake" coil. In winding a pancake coil, a superconductor tape 14 is wound one turn on top of a preceding turn to thereby form a plane of turns perpendicular to the longitudinal axis 16 of the coil (Fig. IA) .
  • Coil 12 is supported by a pair of insulative support members 18 made from a reinforced plastic, for example, G-10 fiberglass.
  • Each support member 18 has a thickness of about 1.25 centimeters, with one or both of the members having a number of openings 20 which allows liquid refrigerant (e.g. , liquid N 2 ) access to the inner windings of the superconductor tape 14 when the coil is immersed in a liquid cryogen dewar.
  • liquid refrigerant e.g. , liquid N 2
  • Fig. 1 is not shown to scale, with the thickness of the coil assembly being exaggerated with respect to the overall size of the coil.
  • the coil assembly typically may have a diameter greater than 1.0 meter with the thickness of the single-layer tape and support members being about 3.25 centimeters.
  • the coil assembly 10 resembles a thin, large diameter, disc-shaped platter.
  • the Q (quality factor) of a coil is defined as the ratio of the stored inductive energy with respect to the dissipation of the coil per cycle. This characteristic is expressed generally by the equation:
  • R eff represents the losses generated in the superconductor tape used to wind the coil which is exposed to an AC magnetic field. These losses include 1) hysteresis losses in the filaments of the tape, 2) coupling currents which flow between the filaments through the silver and then back again, as well as, 3) the eddy current losses associated with the low resistivity silver matrix. At low frequencies (i.e., less than 100 Hz) , ⁇ ff tends to be dominated by the hysteresis losses. On the other hand, at higher frequencies (i.e., above 100 Hz), eddy current losses tend to dominate R eff . At these higher frequencies, the above equation can be expressed as the following equation: n- 12 p ⁇ xfb 2 a 2 V
  • superconductor tape 14 is a high temperature copper oxide ceramic superconducting material, such as Bi 2 Sr 2 Ca 2 Cu 3 ⁇ x , commonly designated BSCCO 2223.
  • the superconductor tape 14 is fabricated as a multi-filament composite conductor having superconducting regions 24 which are approximately hexagonal in cross-sectional shape and extend the length of the multi-filament composite conductor.
  • Superconducting regions 24 form the filaments of the conductor which may include any desired anisotropic superconducting compound.
  • superconducting ceramics of the oxide, sulfide, selenide, telluride, nitride, boron carbide or oxycarbonate types may be used.
  • Superconducting intermetallics as well as metallic superconductors e.g., niobium-tin
  • metallic superconductors e.g., niobium-tin
  • Members of the rare earth (RBCO) family of oxide superconductors; the bismuth (BSCCO) family of oxide superconductors, the thallium (TBSCCO) family of oxide superconductors; or the mercury (HBSCCO) family of oxide superconductors may also be used.
  • the bismuth and rare earth families of oxide superconductors are generally preferred. Thallination, the addition of doping materials, including but not limited to lead and bismuth, variations from ideal stoichiometric proportions and such other variations in the formulation of the desired superconducting oxides as are well known in the art, are also within the scope and spirit of the invention.
  • two-layer and three-layer phases of the bismuth-strontium-calcium-copper-oxide family of superconductors (Bi 2 Sr Ca 1 Cu 1 O ⁇ , also known as BSCCO 2212 and Bi 2 Sr 2 Ca 2 Cu 3 O ⁇ , also known as BSCCO 2223, respectively) are the superconducting oxides most preferred for the operation of the present invention.
  • the filaments are surrounded by a matrix-forming material 26, which conducts electricity, but is not superconducting.
  • a matrix-forming material 26 which conducts electricity, but is not superconducting.
  • Metals generally means a material or homogeneous mixture of materials which supports or binds a substance, specifically including the superconducting oxides or their precursors, disposed within or around the matrix. Metals are typically used. Silver and other noble metals are the preferred matrix materials, but alloys substantially comprising noble metals, including ODS silver, may be used. "Alloy” is used herein to mean an intimate mixture of substantially metallic phases or a solid solution of two or more elements.
  • noble metal is meant a metal which is substantially non-reactive with respect to oxide superconductors and precursors and to oxygen under the expected conditions (temperature, pressure, atmosphere) of manufacture and use.
  • Preferred noble metals include silver (Ag) , gold (Au) , platinum (Pt) and palladium (Pd) .
  • Silver and its alloys, being lowest in cost of these materials, are most preferred for large-scale manufacturing.
  • superconducting regions 24 and the matrix-forming material 26 form the multi-filament composite conductor.
  • the thickness of the multi-filament composite conductor is typically about 0.24 mm.
  • a standard "fill factor" describing the cross-sectional area encompassed by the superconducting regions 24 relative to the overall conductor cross-sectional area is in a range between 10 to 60% (preferably, approximately 30%) .
  • the thickness of the ceramic insulation layer is typically on the order of 10 to 150 ⁇ m.
  • the tape may also be manufactured using other well-known methods including "powder-in-tube” (PIT) forms of tape such as layered laminates or coated tapes in which the superconductor is deposited on the surface of a tape- shaped substrate.
  • PIT "powder-in-tube”
  • superconductors fabricated from HTS materials are anisotropic, meaning that they generally conduct better in one direction than another.
  • the current carrying capacity of well-textured anisotropic superconducting composite articles will depend in large part on the relative orientations of their preferred direction, which is determined by the crystallographic alignment of their superconducting grains, and any current flow or external magnetic field. Because of their crystal structure, supercurrent flows preferentially in at least one of the directions lying within the plane normal to the c axis of each grain. Their critical current may be as much as an order of magnitude lower in their "bad” direction than in their "good” direction. Thus, an important consideration in fabricating high performance wires and tapes from these materials, which is not an issue in conventional tape fabrication, is finding a way to maximize the portions of the tape which do have the desired orientations.
  • the critical current associated with the superconductor structure varies as a function of the orientation of the magnetic field with respect to the crystallographic axes of the superconducting material.
  • the critical current is the current which establishes the point at which the material loses its superconductivity properties and reverts back to its normally conducting state.
  • the radial component of the magnetic field is at a minimum in the central region of a coil where the magnetic field lines are generally parallel with the longitudinal axis of the coil.
  • a single-layer coil 10 with the geometry described above is shown with its magnetic field distribution.
  • the magnitude of the radial field component of the magnetic field (designated by arrow 30) is much less at the outer edges 31 of the superconductor tape of the coil than experienced by a coil positioned at the end of a conventional solenoid coil design.
  • the effective width (w) of the coil has been substantially reduced, losses associated with the radial magnetic field component are also significantly reduced.
  • a desired current carrying capacity characteristic of the coil may be maintained without increasing the volume of superconductor, which would result in a further increase in the conductor loss of the coil.
  • more of the superconducting material lies along the radial axis of the coil. Indeed, the magnitude of the magnetic field is essentially zero at the center of the coil which further contributes to the overall reduction of the losses of the coil.
  • a coil using double pancakes or a multi- pancake stacked configuration still has a relatively large voltage gradient between a turn of one pancake and a corresponding adjacent turn of an adjacent pancake.
  • two turns of adjacent pancakes which forms a double pancake coil are adjacent to each other (i.e., radially spaced from the longitudinal axis of the coil the same distance) , but are spaced a longitudinal distance (i.e., about the width of the individual pancake) .
  • the voltage gradient between these adjacent turns can be relatively significant.
  • a single-width pancake coil in accordance with the invention, provides a much smaller and, therefore, more attractive voltage gradient across the coil.
  • the voltage gradient is small between adjacent overlying turns with the entire voltage gradient of the coil appearing from the inner diameter to the outer diameter of the coil.
  • iron plates 40 spaced from the outer edge of the superconducting coil 12, can further lower the losses of the coil.
  • the iron plates in effect provide a magnetic boundary which prevents dissipation of magnetic energy in the surrounding environment of the coil (e.g., dewar) .
  • the iron plates also further decrease the radial field component of the magnetic field by causing the flux lines 42 to extend in more of a parallel manner across each plate.
  • the use of iron plates for providing this effect is described in co-pending application Serial No. 08/302,358, assigned to the assignee of the present invention and incorporated herein by reference.
  • laminating the iron plates further lowers the conductor losses of the iron.
  • the iron plates are effective from a distance relatively far away from the edges and the coil as well as very close to the edges.
  • the optimum spacing of the iron plates from the edges of the coils for providing the best AC loss characteristic can be determined empirically. With the embodiment shown in Fig. 4, the iron plates are spaced approximately 15 centimeters from the coil.
  • the coil can be separated from the plates by a vacuum barrier formed of an epoxy composite (e.g., G-10 or G-ll) or multilayer insulation (MLI) made of alu inized mylar. Fabrication
  • the superconductor tape 14 may be formed with a number of individual windings of non-insulated tape, wound one over the other, in order to increase the thickness of the tape.
  • this technique allows the thickness of the tape (and, therefore, its current handling capacity) to be increased while allowing the use of standard thickness superconductor tapes.
  • a superconductor tape 14 is shown co-wound with three individual windings 50, 52, 54 and is often referred to as a coil wound "three in hand".
  • the lengths of the tape is generally limited to not more than about 200 meter lengths. Because the superconducting coil of the present invention requires lengths of coil greater than one kilometer (for a one meter diameter coil) , individual lengths of superconducting tape are required to be spliced together. Referring to Fig. 6, short bridging segments 60 of superconducting material used to electrically connect individual lengths of may be superconductor tape together to form a series length of tape which, at present, cannot be manufactured using conventional techniques. The bridging segments are formed of the same Bi 2 Sr 2 Ca 2 Cu 3 O x material used for winding the coils themselves.
  • the bridging segments are generally soldered to the lengths of tape at joint regions.
  • Other bridging materials for example, metal, composite superconductor, or a pure superconductor may also be used.
  • lengths of tape may be spliced directly together using an approach described in U.S. 5,116,810, assigned to the assignee of the present invention and hereby incorporated by reference. In an application requiring several tapes wound several layers
  • the spliced joint between each layer of tape is preferably performed at different positions along their lengths.
  • coil assembly 10 as shown in Figs.
  • the coil 1 and 4 are circularly shaped; however, in other applications the coil may be formed in other shapes commonly used for making magnetic coils, including racetrack and saddle-shaped coils.
  • the concept of the invention is applicable to anisotropic superconducting compounds having monofilament composite conductors.

Landscapes

  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Superconductors And Manufacturing Methods Therefor (AREA)

Abstract

L'invention concerne une bobine magnétique supraconductrice à faibles pertes, présentant une caractéristique Q relativement élevée. La bobine (12) comprend une bande supraconductrice (14) enroulée autour de l'axe longitudinal de la bobine. La bande comprend un supraconducteur composite à multiples filaments. Ce supraconducteur comporte des filaments supraconducteurs individuels entourés ou supportés par un matériau formant matrice. La bobine supraconductrice présente une caractéristique Q supérieure à 250, à une fréquence inférieure à 1000 Hz, la valeur de Q étant définie comme le rapport entre l'énergie d'induction stockée dans la bobine et la dissipation de la bobine par cycle.
EP97906900A 1996-02-09 1997-02-10 Bobine supraconductrice a caracteristique q elevee et a faibles pertes Withdrawn EP1018126A4 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
US59906796A 1996-02-09 1996-02-09
US599067 1996-02-09
PCT/US1997/002093 WO1997029493A1 (fr) 1996-02-09 1997-02-10 Bobine supraconductrice a caracteristique q elevee et a faibles pertes

Publications (2)

Publication Number Publication Date
EP1018126A2 true EP1018126A2 (fr) 2000-07-12
EP1018126A4 EP1018126A4 (fr) 2000-07-12

Family

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Family Applications (1)

Application Number Title Priority Date Filing Date
EP97906900A Withdrawn EP1018126A4 (fr) 1996-02-09 1997-02-10 Bobine supraconductrice a caracteristique q elevee et a faibles pertes

Country Status (3)

Country Link
EP (1) EP1018126A4 (fr)
AU (1) AU2266997A (fr)
WO (1) WO1997029493A1 (fr)

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB201313392D0 (en) * 2013-07-26 2013-09-11 Mcdougall Ian L Conductor for superconducting magnets

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3638154A (en) * 1970-03-26 1972-01-25 Atomic Energy Commission Braided superconductor
WO1995020228A1 (fr) * 1994-01-24 1995-07-27 American Superconductor Corporation Aimant supraconducteur

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3665351A (en) * 1970-07-09 1972-05-23 Gen Electric Superconductive magnets
EP0235809B1 (fr) * 1986-03-05 1992-12-09 Sumitomo Electric Industries Limited Electro-aimants dipolaires supraconducteurs et leur méthode de fabrication
JP2726499B2 (ja) * 1989-07-06 1998-03-11 古河電気工業株式会社 超電導利用機器
US5189260A (en) * 1991-02-06 1993-02-23 Iowa State University Research Foundation, Inc. Strain tolerant microfilamentary superconducting wire

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3638154A (en) * 1970-03-26 1972-01-25 Atomic Energy Commission Braided superconductor
WO1995020228A1 (fr) * 1994-01-24 1995-07-27 American Superconductor Corporation Aimant supraconducteur

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See also references of WO9729493A1 *

Also Published As

Publication number Publication date
WO1997029493A1 (fr) 1997-08-14
AU2266997A (en) 1997-08-28
EP1018126A4 (fr) 2000-07-12

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