US-12620514-B2 - Conformal winding and current-sharing in a dipole magnet using superconducting tape conductor

US12620514B2US 12620514 B2US12620514 B2US 12620514B2US-12620514-B2

Abstract

A conformal dipole winding includes a superconducting tape configured with a geometry that orients a face of the superconducting tape to be parallel to a local magnetic field produced by the winding along a length of the superconducting tape. The superconducting tape forms a tape-stack cable formed from a stack of a plurality of the superconducting tapes. A face of each of the superconducting tapes is oriented parallel to the local magnetic field and is in face-face contact with adjacent superconducting tapes.

Inventors

Peter McIntyre
John Scott Rogers

Assignees

THE TEXAS A&M UNIVERSITY SYSTEM
ACCELERATOR TECHNOLOGY CORP.

Dates

Publication Date: 20260505
Application Date: 20211021

Claims (9)

1 . A conformal dipole winding comprising a superconducting tape configured with a geometry that orients a face of the superconducting tape to be parallel to a local magnetic field produced by the winding along a length of the superconducting tape, wherein the superconducting tape forms a tape-stack cable comprising a stack of a plurality of the superconducting tapes, a copper cladding on all surfaces of each superconducting tape, and a face of each of the copper-clad superconducting tapes which is oriented closely parallel to the local magnetic field and is in face-face contact with adjacent superconducting tapes, further comprising a laminar spring contacting the innermost face of each tape-stack cable, or alternatively the innermost fact of each stack of turns of tape-stack cable, the laminar spring comprising two strips of high-strength metal alloy that form an arched spring and are welded to one another along their common edges to provide a compliant spring action over a range of compression, and further comprising a steel flux return assembly, wherein turns of the tape-stack cable and inner boundaries of the steel flux return assembly are arranged so that all turns of the tape-stack cable are conformal to the local magnetic field at the location of the cable turn; and wherein one turn of the tape-stack cable is located at a position where it selectively controls the sextupole component of the local magnetic field distribution in an aperture of the conformal dipole winding.
2 . The conformal dipole winding of claim 1 wherein the laminar spring is located in a cavity between an inner structural element of a winding core of the conformal dipole and an inner boundary face of a turn of the tape-stack cable and is configured to provide an outwardly directed force to compress the tape-stack cable against a boundary surface of an outer structural element of the winding core.
3 . The conformal dipole winding of claim 1 , further comprising an assembly of inner and outer structural elements and a cavity that supports turns of the tape-stack cable against Lorentz forces that operate upon the superconducting currents flowing within the superconducting tapes of the tape-stack cable in the conformal dipole winding.
4 . A flared-end winding assembly of a conformal dipole, the flared-end winding assembly comprising: a tape-stack cable comprising a plurality of superconducting tapes, wherein a face of each of the plurality of superconducting tapes is oriented parallel to a local magnetic field of the flared-end winding assembly; wherein turns of each tape-stack cable of the flared-end winding sub-assembly are connected continuously to a corresponding turn of the tape-stack cable on an opposite side of the conformal dipole by a connecting segment that follows a catenary curve that is tangent to and continuous with straight portions of the plurality of superconducting tapes of the tape-stack cable in the body region of the dipole; and wherein the catenary curve includes a deflection out of a plane of symmetry of the flared-end winding assembly that accommodates a beam tube through a dipole aperture of the conformal dipole and also maintains the local face orientation of the tapes to be closely parallel to the flaring vector magnetic field at each location within the flared-end sub-assembly.
5 . The flared-end winding sub-assembly of claim 4 , wherein a superconducting tape segment is sandwiched between each pair of neighboring superconducting tapes in each turn of the flared-end winding sub-assembly so that the superconducting tape segment is compressed to provide for low-resistance current transfer from the pair of neighboring superconducting tapes to stabilize current transport.
6 . The flared-end winding sub-assembly of claim 5 , wherein the flared-end winding assembly is impregnated with an electrically insulating medium to form a rigid assembly that immobilizes the flared-end winding assembly against Lorentz forces.
7 . A hybrid-coil magnet comprising: a conformal dipole winding comprising a superconducting tape-stack cable and configured as an inner sub-winding; and an outer sub-winding of a cable-in-conduit comprising superconducting wires, wherein the inner sub-winding and the outer sub-winding are assembled onto an inner core structure and preloaded inside a steel flux return assembly.
8 . The hybrid-coil dipole magnet of claim 7 , wherein the superconducting wires comprise Nb3Sn.
9 . The hybrid-coil dipole magnet of claim 7 , wherein the conformal dipole winding comprises a superconducting tape configured with a geometry that orients a face of the superconducting tape to be parallel to a local magnetic field produced by the winding along a length of the superconducting tape in all regions of the body and flared ends of the dipole winding.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This patent application claims priority from, and incorporates by reference the entire disclosure of, U.S. Provisional Application 63/198,470 filed on Oct. 21, 2020. TECHNICAL FIELD The present disclosure relates generally to dipole electromagnets and more particularly, but not by way of limitation to dipole electromagnets using thin tapes of REBCO that operate with maximum current density. BACKGROUND OF THE INVENTION This section provides background information to facilitate a better understanding of the various aspects of the disclosure. It should be understood that the statements in this section of this document are to be read in this light, and not as admissions of prior art. Dipole electromagnets are used to deflect a charged particle bunch along a circular trajectory so that the charged particle passes through an aperture of the dipole electromagnet to circulate the charged particle in an orbit of constant radius in a particle accelerator. The ring of dipole electromagnets is typically the most expensive component of an accelerator. The maximum magnetic field strength B0 in the aperture of the dipole electromagnet determines the momentum p of particles that can circulate in an accelerator of radius R: p=qB/cREq. (1)where q is the electric charge of the charged particles. The winding of a dipole accelerator electromagnet comprises a multiplicity of electrically insulated turns of a conducting wire or cable that are wrapped in a uniform cross-section around a support structure containing the aperture of the dipole. The conducting wire or cable is flared at ends of the dipole to accommodate the beam tube that conveys the particles in the accelerator. FIG. 1 shows a cross-section of a superconducting CIC, containing 15 wires of NbTi/Cu wire cabled around a perforated center tube and confined within an outer sheath tube. A magnetic field distribution is generated within the dipole aperture when an electric current is passed through the winding. The magnetic field in the dipole is also present in the winding itself, with strength {right arrow over (B)}n at the location of the nth turn of the winding, and the field {right arrow over (B)}n at the location of the nth tape produces a Lorentz force {right arrow over (F)}in on the current flowing within each length {right arrow over (L)}n of that conductor: F→l⁢n=I⁢L→n×B→n.Eq. (2) One limitation to the performance of a dipole magnet is the maximum field strength that can be created in its aperture. The winding can be made from a wire or cable of a superconductor, for example round wire of NbTi, Nb3Sn, or Bi-2212, or thin tapes of REBCO. Providing that the winding is operated at a temperature T that is below the critical temperature Tc of the superconductor, the winding can operate without dissipation of ohmic heat so long as the winding current does not exceed the critical current Ic(Bn,Tn), which value depends upon the magnetic field B n and the temperature T n in that turn of the winding. A second limitation to the performance of a dipole magnet containing windings of REBCO tape is that the critical current Ic(Bn, Tn, θ) is a function of the relative angle θ between the face-normal vector of the tape surface and the magnetic field vector, as illustrated in FIGS. 3A and 3B. In prior art for dipoles containing REBCO tape windings, θ˜0° much different from the favorable orientation θ˜90° in a multitude of locations within the winding, so that the superconducting current that can be supported is much less than would be the case in the favorable orientation. A third limitation to the performance of a dipole magnet containing windings of REBCO tape arises for applications in which a high magnetic field strength is required. In such cases the winding must be made using a tape-stack cable of individual tapes which are clustered with normal-state electrical contact among them so that the cable current is shared among the tapes within the tape-stack cable. For such cases the REBCO tape is coated with a layer of copper, and the copper coatings of neighboring tapes are in normal-state resistive contact within the tape-stack cable. It is difficult to maintain uniform low-resistance contact resistance among the copper surfaces of neighboring tapes at all locations within a winding, so that current-sharing is problematic and can produce local ohmic heating that reduces or quenches the superconducting current capacity of the tape-stack cable. Current-sharing is further compromised because the Lorentz force upon the currents in all tapes of the tape-stack cable acts to re-direct current that flows in inner tapes of each tape-stack cable (near the inside of the overall winding geometry) to flow instead in the outer tapes of the tape-stack cable, so that those tapes reach capacity prematurely and the tape-stack cable superconducting current capacity is correspondingly reduced. SUMMARY OF THE INVENTION The design of an accelerator dipole