Superconducting magnets with thermal radiation shields
A cylindrical superconducting magnet has a number of axially-aligned annular coils of superconducting wire, arranged for cooling by thermal conduction through a cooled surface in mechanical contact with the coils. The coils are provided with a cryogenic radiation shield located between respective radially inner surfaces of the coils and respective axes of the coils. The cryogenic radiation shield is formed of a metal layer in thermal contact with the cooled surface.
1. A cylindrical superconducting magnet structure, comprising:
a plurality of resin-impregnated, axially aligned annular coils of superconducting wire, each coil having an axis around which the coil is wound, and a radially outer surface and a radially inner surface;
a tubular support structure at least partially surrounding the respective radially outer surfaces of said annular coils and having a larger diameter than said radially outer surfaces, each of said annular coils exhibiting a thermal resistance between the respective annular coil and the tubular support structure;
a cooling arrangement in thermal communication with said tubular support structure that cools at least said tubular support structure to a cryogenic temperature; and
a cryogenic radiation shield between the respective radially inner surfaces of the annular coil and the respective axes of the annular coils, said cryogenic radiation shield comprising a metal cylinder mechanically joined to the tubular support structure at a plurality of axial and circumferential intervals, and comprising a plurality of thermally linking structures that thermally link the metal cylinder to the tubular support, each of said thermally linking structures having a thermal resistance that produces a thermal resistance between the metal cylinder and the tubular support structure that is less than the respective thermal resistances between the annular coils and the tubular support structure.
2. A cylindrical superconducting magnet structure as claimed in claim 1 wherein said metal cylinder comprises a plurality of sub-cylinders, each mechanically and thermally joined to said tubular support structure.
3. A cylindrical superconducting magnet structure as claimed in claim 1 wherein each of said plurality of axial and circumferential intervals is 0.3 m or less.
4. A cylindrical superconducting magnet structure as claimed in claim 1 wherein said metal cylinder comprises a cylinder formed of a first metal having a first electrical conductivity that is mechanically and thermally joined to said tubular support structure, and a cladding formed of a second metal having a second electrical conductivity, which is larger than said first conductivity, applied to a radially inner surface of said cylinder formed of said first metal.
5. A cylindrical superconducting magnet structure as claimed in claim 4 wherein said cladding is comprised of aluminum having at least 99.999% purity.
6. A cylindrical superconducting magnet structure as claimed in claim 1 wherein said metal cylinder has a radially inner surface, and comprising a pattern of further superconducting wires applied to said radially inner surface of said metal cylinder.