Cryogen-free magnet system comprising a magnetocaloric heat sink
A cryostat system is kept at a cryogenic operating temperature without providing or supplying cryogenic fluids by a cryocooler. The cryostat system includes a superconducting magnet arrangement and a heat sink apparatus to prolong the time before the superconducting magnet arrangement quenches/returns to the normally conducting state if active cooling fails. The heat sink apparatus includes magnetocaloric material and is thermally connected to the superconducting magnet arrangement and/or to parts of the cryostat system through which ambient heat can flow to the superconducting magnet arrangement. In this way, the cryostat system can be operated in a truly “cryogen-free” manner while maintaining a sufficiently long time to quench in the event of potential operational malfunctions.
1. A cryostat system configured to be kept at a cryogenic operating temperature in a dry manner without providing or supplying cryogenic fluids, the cryostat system comprising:
a cryocooler configured to provide active cooling without cryogenic fluid;
a superconducting magnet arrangement; and
a heat sink apparatus comprising a magnetocaloric material, and configured to prolong a time to quench before the superconducting magnet arrangement returns to a normally conducting state if the active cooling fails, wherein the heat sink apparatus is thermally connected to the superconducting magnet arrangement or to parts of the cryostat system, through which ambient heat flows to the superconducting magnet arrangement.
2. The cryostat system according to claim 1 , wherein the parts of the cryostat system, through which ambient heat flows to the superconducting magnet arrangement, comprise parts of the cryocooler, radiation shields, or mechanical suspension devices for the superconducting magnet arrangement.
3. The cryostat system according to claim 1 , wherein the heat sink apparatus is arranged relative to the superconducting magnet arrangement to minimize magnetic fields from the superconducting magnet arrangement at the magnetocaloric material.
4. The cryostat system according to claim 3 , wherein the magnetic fields from the superconducting magnet arrangement at the magnetocaloric material are less than 2 Tesla after a demagnetization process.
5. The cryostat system according claim 1 , further comprising a temperature control device configured to keep the temperature of the magnetocaloric material constant during normal operation.
6. The cryostat system according to claim 1 , wherein the heat sink apparatus includes at least one magnetic coil.
7. The cryostat system according to claim 6 , wherein the magnet coil of the heat sink apparatus is superconductively short-circuited when in operation.
8. The cryostat system according to claim 6 , wherein the magnet coil of the heat sink apparatus is electrically connected to the superconducting magnet arrangement.
9. The cryostat system according to claim 8 , wherein the magnet coil of the heat sink apparatus is electrically connected in series to the superconducting magnet arrangement.
10. The cryostat system according to claim 9 , wherein the magnet coil of the heat sink apparatus and the superconducting magnet arrangement are spatially arranged and electrically interconnected to form a magnetic field-generating coil.
11. The cryostat system according to claim 1 , further comprising a magnetic shield that surrounds the heat sink apparatus.
12. The cryostat system according to claim 11 , wherein the magnetic shield surrounds a magnet coil of the heat sink apparatus.
13. The cryostat system according to claim 11 , wherein the magnetic shield includes an active shield magnet coil.
14. The cryostat system according to claim 11 , wherein the magnetic shield is a passive magnet shield arrangement.
15. The cryostat system according to claim 14 , wherein the passive magnet shield arrangement comprises a superconducting material, soft iron, or a short-circuited coil made of superconducting wire.
16. The cryostat system according to claim 1 , wherein the superconducting magnet arrangement comprises high temperature superconducting (HTS) elements.
17. The cryostat system according to claim 1 , wherein the cryostat system is part of a magnetic resonance equipment.
18. The cryostat system according to claim 1 , wherein the magnetocaloric material of the heat sink apparatus comprises gadolinium gallium garnet (GGG), dysprosium gallium garnet (DGG), gallium lithium fluoride (GLF), or dysprosium aluminum garnet (DAG).