Solenoidal magnets having supported outer coils
In a solenoidal electromagnet arrangement for a magnetic resonance imaging system, annular inner coils and annular end coils are provided, all concentrically aligned about an axis, the end coils being placed at axial extremities, axially outside of the inner coils. A pair of annular outer coils are provided concentrically aligned about the axis. An arrangement is provided retaining the pair of outer coils against an axial force urging the outer coils away from one another. The arrangement comprises strap elements which extend around a radially inner surface, a radially outer surface and an axially outer surface of each outer coil in certain circumferential locations. Each strap element on one of the outer coils is linked to a corresponding strap element on the other outer coil of the pair by a tensile member.
1. A solenoidal electromagnet arrangement for a magnetic resonance imaging system, comprising:
annular inner coils and annular end coils, all concentrically aligned about an axis, the end coils being placed at axial extremities, axially outside of the inner coils;
a pair of annular outer coils concentrically aligned about the axis; and
an arrangement retaining the pair of outer coils against an axial force urging the outer coils away from one another, said arrangement comprising strap elements which extend around a radially inner surface, a radially outer surface and an axially outer surface of each outer coil in certain circumferential locations, each strap element on one of the outer coils being linked to a corresponding strap element on the other outer coil of the pair by a tensile member.
2. An arrangement according to claim 1 wherein the outer coils are held concentric with said inner coils and end coils by support frames which are mechanically joined to a support structure of the inner coils and/or the end coils and mechanically joined to the tensile members.
3. An arrangement according to claim 2 wherein a length of the tensile members is adjustable.
4. An arrangement according to claim 2 wherein support frames are mechanically linked to the corresponding tensile members at or near radially outer extremities of the support frames.
5. An arrangement according to claim 1 wherein the tensile members are flexible.
6. An arrangement according to claim 1 wherein at least one of the outer coils is retained within a journal, and the strap elements surround the journal and the coil therein.
7. An arrangement according to claim 1 wherein a slip plane material is placed between the radially inner surface of one of the outer coils and an adjacent surface of the associated strap element, and between the radially outer surface of the outer coil and the adjacent surface of the strap element.
8. An arrangement according to claim 1 wherein a filler material is positioned between the axially outer surface of one of the outer coils and the axially outer end of the associated strap element.
9. An arrangement according to claim 1 wherein one of the outer coils is impregnated with a hardened material, and the associated strap elements are bonded to the coil by the hardened material.