# US 5,701,744 A · Magnetic resonance imager with helium recondensing > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 5,701,744 A - Document ID: US5701744A - Status: Granted - Kind: A - Application number: 08/741,993 - Filed: 1996-10-31 - Granted: 1997-12-30 - Earliest claimed: 1996-10-31 - Assignees: General Electric Company - Inventors: Phillip William Eckels; Kazuhiko Sato; Daniel Christian Woods; Granville Geer Ward; Gregory Farin Hayworth; Christopher G. King - Web page: https://patentgrep.com/patent/US5701744A ## CPC - G01R 33/3815: with superconducting coils, e.g. power supply therefor - F17C 13/02: Special adaptations of indicating, measuring, or monitoring equipment (measuring in general G01) - F25D 19/006: {Thermal coupling structure or interface} - H01F 6/04: Cooling - F17C 2221/017: Helium - F17C 2223/0161: cryogenic, e.g. LNG, GNL, PLNG - F17C 2227/0353: using cryocooler - F25B 2400/17: Re-condensers - G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12) - F17C: VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES (storing fluids in natural or artificial cavities or chambers in the earth B65G5/00; construction or assembling of bulk storage containers employing civil-engineering techniques E04H7/00; variable-capacity gas-holders F17B; liquefaction or refrigeration machines, plants, or systems F25) - F25D: REFRIGERATORS; COLD ROOMS; ICE-BOXES; COOLING OR FREEZING APPARATUS NOT OTHERWISE PROVIDED FOR (refrigerated showcases A47F3/04; thermally-insulated vessels for domestic use A47J41/00; refrigerated vehicles, see the appropriate subclasses of classes B60 - B64; containers with thermal insulation in general B65D81/38; heat-transfer, heat-exchange or heat-storage materials, e.g. refrigerants, or materials for the production of heat or cold by chemical reactions other than by combustion C09K5/00; thermally-insulated vessels for liquefied or solidified gases F17C; air-conditioning or air-humidification F24F; refrigeration machines, plants, or systems F25B; cooling of instruments or comparable apparatus without refrigeration G12B) - H01F: MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES - F25B: REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS ## Abstract A cryogen recondensing system magnetic resonance imager superconducting magnet and a cryogen recondensing system with a rare earth displacement material cryocooler and superconductive lead bismuth magnetic sleeve provides superconducting current flow of currents induced by movement of the rare earth displacer which generate opposing magnetic fields to shield the superconducting magnet from the magnetic interference of the cryocooler rare earth displacer. Strips of high conductivity wave-shaped aluminum or sapphire rods may be embedded in the surface of the sleeve to lower the thermal resistance of the superconducting shield to enable it to quickly reach superconducting temperature. ## Claims ### Claim 1 A cryogen recondensing system with a mechanical cryocooler utilizing a rare earth displacer for a magnetic resonance imager superconducting magnet comprising: a sleeve surrounding said cryocooler rare earth displacer; said sleeve being magnetically coupled to the magnetic fields generated by the movement of said rare earth displacer; said sleeve including a lead alloy which provide superconducting flow of currents induced in said shield by said magnetic fields; and high thermal conductivity members along the surface of said sleeve; said superconducting current flow opposing said induced magnet fields to shield said superconducting magnet from said magnetic fields generated by said movement of said rare earth displacer; and said cryocooler thermally connected to cryogen recondensing means. ### Claim 2 (depends on 1) The superconducting magnet cryogen recondenser of claim 1 wherein high thermal conductivity members are positioned along the surface of said sleeve. ### Claim 3 (depends on 2) The superconducting magnetic cryogen recondenser of claim 2 wherein said superconducting magnet includes a closed cavity therein and said cryocooler is removably positioned within said cavity. ### Claim 4 (depends on 2) The superconducting magnet cryogen recondenser of claim 2 wherein said sleeve is a lead-bismuth alloy and said thermal conductivity members are aluminum strips to reduce the thermal resistance of said sleeve. ### Claim 5 (depends on 4) The superconducting magnet cryogen recondenser of claim 4 wherein said aluminum strips high purity aluminum bent into a wave pattern within grooves on said sleeve and a polymer interface is provided between said aluminum and said sleeve. ### Claim 6 (depends on 5) The superconducting magnet cryogen recondenser of claim 5 in which said wave pattern of said aluminum strips is approximately sinusoidal. ### Claim 7 (depends on 6) The superconducting magnet cryogen recondenser of claim 6 wherein said aluminum strips have a cross-section of approximately 1.5 by 2.0 millimeters with in excess of ten slots axially spaced around the circumference of said sleeve. ### Claim 8 (depends on 2) The superconducting magnet cryogen recondenser of claim 2 wherein said sleeve is a lead bismuth alloy and includes a plurality of embedded sapphire rods to reduce the thermal resistance of said sleeve. ### Claim 9 (depends on 3) The superconducting magnet cryogen recondenser of claim 3 wherein said lead alloy is approximately 15.5 parts by weight tin, 32 parts lead and 52.5 parts bismuth. ### Claim 10 (depends on 3) The superconducting magnet cryogen recondenser of claim 3 wherein said lead alloy includes approximately 40-46 parts bismuth and 60-54 parts lead. ### Claim 11 (depends on 1) The superconducting magnet cryogen recondenser of claim 1 wherein said lead alloy is approximately 48 parts lead, 13 parts cadmium and 13 parts tin. ### Claim 12 (depends on 3) The superconducting magnet cryogen recondenser of claim 3 wherein said sleeve is positioned around said cavity. ### Claim 13 (depends on 12) The superconducting magnet cryogen recondenser of claim 12 wherein said cryocooler is a multi-stage cryocooler and said magnetic shield surrounds the coldest stage of said cryocooler. ### Claim 14 (depends on 3) The superconducting magnet cryogen recondenser of claim 3 wherein said cryogen is helium. ### Claim 15 (depends on 13) The superconducting magnet cryogen recondenser of claim 13 wherein said aluminum strips are positioned in axial extending grooves on the outer surface of said sleeve and retained in place. ### Claim 16 (depends on 14) The superconducting magnet cryogen recondenser of claim 14 wherein said aluminum strips are retained in place by retaining members comprising deformations of said sleeve overlying portions of said aluminum strips. ### Claim 17 (depends on 14) The superconducting magnet cryogen recondenser of claim 14 wherein said shield is approximately 1/8 inches thick, said cryocooler is a multi-stage cryocooler, and said shield surrounds the coldest stage of said multi-stage cryocooler. ### Claim 18 (depends on 4) The superconducting magnet cryogen recondenser of claim 4 wherein said cryocooler includes an outer housing and said sleeve closely fits around said cryocooler housing with thermal grease between said housing and said sleeve.