Cooling arrangement for a superconducting magnet structure for an MRI system
A superconducting magnet structure has a number of axially aligned superconducting inner magnet coils that form an inner magnet structure (30) and a number of superconducting outer coils each having an inner diameter greater than an outer diameter of each of the inner magnet coils. The inner magnet structure is enclosed within a cryogen vessel, and the outer coils are located outside of the cryogen vessel, in thermal contact with a cooling arrangement for cooling the outer coils.
1. A superconducting magnet structure comprising:
a number of axially aligned superconducting inner magnet coils that form an inner magnet structure and a number of superconducting outer coils each having an inner diameter greater than an outer diameter of each of the inner magnet coils;
a cryogen vessel in which the inner magnet structure is enclosed, with the outer coils located outside of the cryogen vessel
a cooling arrangement in thermal contact with the outer coils for cooling the outer coils; and
said cooling arrangement for the outer coils comprising respective heat exchangers in thermal and mechanical contact with respective outer coils, each heat exchanger having a cryogen tube, with upper and lower extremities of each cryogen tube being in communication with the cryogen vessel respectively at or near upper and lower extremities of the cryogen vessel.
2. A superconducting magnet structure according to claim 1 , wherein the cryogen tube is extruded.
3. A superconducting magnet structure according to claim 1 , wherein the heat exchangers are structural members held in position by a mechanical support structure mounted on the cryogen vessel, and wherein the heat exchangers retain the outer coils ( 32 ) in place.
4. A superconducting magnet structure comprising:
a number of axially aligned superconducting inner magnet coils that form an inner magnet structure and a number of superconducting outer coils each having an inner diameter greater than an outer diameter of each of the inner magnet coils;
a cryogen vessel in which the inner magnet structure is enclosed, with the outer coils located outside of the cryogen vessel
a cooling arrangement in thermal contact with the outer coils for cooling the outer coils; and
the cooling arrangement for the outer coils comprising a thermal link to the cryogen vessel.
5. A superconducting magnet structure according to claim 4 wherein the thermal link comprises a thermal bus bar, laminate or braid.
6. A superconducting magnet structure according to claim 4 comprising a thermally conductive mechanical support structure to which the outer coil as are attached, said support structure being thermally linked to the cryogen vessel by the thermal link.
7. A superconducting magnet structure according to claim 4 wherein the thermal link joins an outer coil to the cryogen vessel.
8. A superconducting magnet structure according to claim 1 comprising an outer vacuum container (OVC) enclosing said cryogen vessel, said outer coils, and said cooling arrangement with said heat exchangers and said cryogen tube.
9. A superconducting magnet structure according to claim 8 comprising support structures that support the cryogen vessel within the OVC support structures comprising rods or bands of stainless steel.
10. A superconducting magnet structure according to claim 1 , wherein the cryogen vessel comprises a cylindrical enclosure, comprising inner and outer cylindrical walls joined by annular end walls, the annular end walls being planar surfaces.
11. A superconducting magnet structure according to claim 1 , comprising electrical termination and connections and switches housed at or near the bottom of the cryogen vessel.
12. A superconducting magnet structure according to claim 11 , comprising a sump at the bottom of the cryogen vessel, with the terminations, connections and switches being located in said sump.
13. A superconducting magnet structure according to claim 11 , wherein the outer coils are electrically connected to the terminations, connections and switches in the cryogen vessel.
14. A superconducting magnet structure according to claim 8 , wherein the cryogen vessel is mechanically suspended from the OVC, and the outer coils and the associated heat exchangers are mechanically supported from the cryogen vessel.
15. A superconducting magnet structure according to claim 1 , further comprising at least one additional gas buffer tank vertically above the inner magnet structure and in communication with the cryogen vessel through at least one linking tube.