Layout for magnet coils wound with anisotropic superconductor, and method for laying out the same

1. A coil arrangement comprising:

a hollow coil with a constant inner radius about an axis of symmetry to generate a magnetic field in a working volume, wherein the hollow coil has windings of an anisotropic superconductor with a superconducting current-carrying capacity in a magnetic field perpendicular to a current direction in the anisotropic superconductor depending on both a magnetic field amplitude and a magnetic field direction in a plane perpendicular to the current direction; and

a sectional plane which includes the axis of symmetry and which intersects the hollow coil, wherein the hollow coil has a rectangular coil cross-section in the sectional plane that is defined by a radially inner edge, a radially outer edge, a first axial edge, and a second axial edge, the radially inner edge defined by a radially innermost winding of the hollow coil, the radially outer edge defined by a radially outermost winding of the hollow coil, the first axial edge defined by an axially first winding of the hollow coil with a smallest coordinate along a direction of the axis of symmetry, and the second axial edge defined by an axially last winding of the hollow coil with a greatest coordinate along the direction of the axis of symmetry, wherein the hollow coil includes:

a first coil region that fully overlaps the rectangular coil cross-section along the direction of the axis of symmetry and contains no layer which is fully wound in the axial direction, wherein the layer is a region limited in the axial direction by a length of the hollow coil and in a radial direction by a constant radius;

a second coil region within the first coil region, the second coil region fully overlapping the first coil region radially and overlapping 10% of the first coil region along the direction of the axis of symmetry and including the first axial edge or second axial edge;

a third coil region inside the first coil region, the third coil region fully overlapping the first coil region radially and overlapping 40% of the first coil region along the direction of the axis of symmetry and abutting the second coil region, wherein a number of windings of the anisotropic superconductor in the third coil region is at least four and one-half times a number of windings of the anisotropic superconductor in the second coil region;

a fourth coil region inside the rectangular coil cross-section, the fourth coil region fully overlapping the rectangular coil cross-section radially, overlapping 10% of the rectangular coil cross-section along the direction of the axis of symmetry, and including the first axial edge, wherein a first number of coil edge windings is determined by a number of windings of the anisotropic superconductor in the fourth coil region; and

a fifth coil region inside the rectangular coil cross-section, the fifth coil region fully overlapping the rectangular coil cross-section radially and overlapping 10% of the rectangular coil cross-section along the direction of the axis of symmetry, and including the second axial edge, wherein a second number of coil edge windings is determined by the number of windings of the anisotropic superconductor in the fifth coil region;

wherein a maximum number of coil edge windings is determined by a quotient of a cross-sectional area of the fourth coil region or a cross-sectional area of the fifth coil region and a cross-sectional area of the anisotropic superconductor,

wherein the windings of the anisotropic superconductor are layer wound with cylindrical symmetry about the axis of symmetry,

wherein the windings of the anisotropic superconductor are laid out in such a manner that the generated magnetic field has a field component B r perpendicular to the current direction and to the axis of symmetry, the maximum of the field component B r in the windings of the anisotropic superconductor being at least 5% lower than a comparable field component B r generated by a comparable coil that generates the same magnetic field in the center of the working volume with lengths of the fourth coil region and fifth coil region shortened along the axis of symmetry toward a center of the comparable coil,

wherein the lengths of the fourth coil region and the fifth coil region are shortened by a ratio of the first number of coil edge windings to the maximum number of coil edge windings in the fourth coil region, as well as a ratio of the second number of coil edge windings to the maximum number of coil edge windings in the fifth coil region, with the number of windings of the anisotropic superconductor in the comparable coil remaining the same as the number of windings of the anisotropic superconductor in the hollow coil,

wherein a minimum of the superconducting current-carrying capacity of the anisotropic superconductor in the hollow coil is at least 3% higher than a superconducting current-carrying capacity of the anisotropic superconductor in the comparable coil, and

wherein non-superconducting material is wound together with the anisotropic superconductor in the first coil region toward the first axial edge and the second axial edge along the axis of symmetry.

2. The coil arrangement according to claim 1 , wherein the second coil region is wound with at least 20% fewer conductor windings than an axially adjoining coil region of the same geometry.

3. The coil arrangement according to claim 2 , wherein the second coil region is wound with 40% to 60% fewer conductor windings than the axially adjoining coil region of the same geometry.

4. The coil arrangement according to claim 3 , wherein the second coil region is wound with 50% fewer conductor windings than the axially adjoining coil region of the same geometry.

5. The coil arrangement according to claim 1 , wherein the maximum of the field component B r in the windings of the anisotropic superconductor is at least 10% lower than a field component B r in the comparable coil.

6. The coil arrangement according to claim 5 , wherein the maximum of the field component B r in the windings of the anisotropic superconductor is up to 50% lower than a field component B r in the comparable coil.

7. The coil arrangement according to claim 1 , wherein the minimum of the superconducting current-carrying capacity of the anisotropic superconductor is at least 5% higher than a minimum of the superconducting current-carrying capacity of the anisotropic superconductor in the comparable coil.

8. The coil arrangement according to claim 7 , wherein the minimum of the superconducting current-carrying capacity of the anisotropic superconductor is at least 30% higher than a minimum of the superconducting current-carrying capacity of the anisotropic superconductor in the comparable coil.

9. The coil arrangement according to claim 8 , wherein the minimum of the superconducting current-carrying capacity of the anisotropic superconductor is up to 50% higher than a minimum of the superconducting current-carrying capacity of the anisotropic superconductor in the comparable coil.

10. The coil arrangement according to claim 1 , wherein the number of windings of the anisotropic superconductor in the fourth coil region or the number of windings of the anisotropic superconductor in the fifth coil region decreases toward the first axial edge or the second axial edge, respectively, in discrete steps along the axis of symmetry.

11. The coil arrangement according to claim 1 , wherein the number of windings of the anisotropic superconductor in the fourth coil region or the number of windings of the anisotropic superconductor in the fifth coil region decreases toward the first axial edge or the second axial edge quasi-continuously along the axis of symmetry (z).

12. The coil arrangement according to claim 1 , wherein windings in the first coil region are wound from a single, continuous superconductor piece.

13. The coil arrangement according to claim 1 , wherein the non-superconducting material comprises foil inserts.

14. A method for laying out a coil arrangement according to claim 1 , comprising:

proceeding from a coil arrangement with a coil of the anisotropic superconductor which is layer wound with cylindrical symmetry about the axis of symmetry, and

winding non-superconducting material together with the anisotropic superconductor in the first coil region toward the edge along the axis of symmetry, wherein the superconducting current-carrying capacity of the coil is limited on axial ends by the field component B r with a maximum radial magnetic field component minimized by reducing a number of windings in optimization regions of the coil comprising the fourth coil region and the fifth coil region, wherein the superconducting current-carrying capacity of the coil is increased by varying at least one parameter selected from:

a size of the optimization regions in which the number of windings is reduced,

the number of windings in the optimization regions, and

a distribution of windings in the optimization regions.