EP0350266B1 - Coupling a cryogenic cooler to a body to be cooled - Google Patents

Coupling a cryogenic cooler to a body to be cooled Download PDF

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Publication number
EP0350266B1
EP0350266B1 EP89306786A EP89306786A EP0350266B1 EP 0350266 B1 EP0350266 B1 EP 0350266B1 EP 89306786 A EP89306786 A EP 89306786A EP 89306786 A EP89306786 A EP 89306786A EP 0350266 B1 EP0350266 B1 EP 0350266B1
Authority
EP
European Patent Office
Prior art keywords
sleeve
flange
cryocooler
cryostat
stage
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
EP89306786A
Other languages
German (de)
English (en)
French (fr)
Other versions
EP0350266A2 (en
EP0350266A3 (en
Inventor
Steven Joseph Brzozowski
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
General Electric Co
Original Assignee
General Electric Co
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by General Electric Co filed Critical General Electric Co
Publication of EP0350266A2 publication Critical patent/EP0350266A2/en
Publication of EP0350266A3 publication Critical patent/EP0350266A3/en
Application granted granted Critical
Publication of EP0350266B1 publication Critical patent/EP0350266B1/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25D—REFRIGERATORS; COLD ROOMS; ICE-BOXES; COOLING OR FREEZING APPARATUS NOT OTHERWISE PROVIDED FOR
    • F25D19/00—Arrangement or mounting of refrigeration units with respect to devices or objects to be refrigerated, e.g. infrared detectors
    • F25D19/006—Thermal coupling structure or interface
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F6/00—Superconducting magnets; Superconducting coils
    • H01F6/06—Coils, e.g. winding, insulating, terminating or casing arrangements therefor
    • H01F6/065—Feed-through bushings, terminals and joints

Definitions

  • the present invention relates to an arrangement for coupling a cryogenic cooler to a body or device to be cooled.
  • the invention relates for example to a direct contact thermal interface for demountably interconnecting a multi-stage cryocooler and a magnetic resonance (MR) magnet.
  • MR magnetic resonance
  • Cryocoolers using the Gifford-McMahon cycle can achieve low temperatures at their heat stations for removing heat from the interior of superconducting magnets.
  • the heat stations in a two stage cryocooler are located at the end of the first and second stages of the cold head portion of the cryocooler.
  • high contact forces are needed as well as soft metal interfaces in order to achieve low thermal resistances. Since the cryocooler is removable, heavy frost can accumulate at the interface when the cryocooler is removed for servicing. Re-establishing the connection in the presence of heavy frost can be difficult.
  • Differential expansion or contraction between a two stage cryocooler and the interface receptacle can also interfere with the formation of thermally efficient contact resistances.
  • a superconductor magnet cooled by a multistage cryocooler (8) comprising:
  • the axially flexible portion of the first sleeve and the second sleeve wall each comprises stainless steel cylindrical bellows.
  • the magnet further comprises means for limiting the axial travel of the first flange towards the cryostat when the cryocooler is not in the first sleeve, the means situated between the cryostat and the first flange.
  • Such an arrangement can be so made that it provides a cryocooler cold head interface receptacle for making reliable contacts with low thermal resistance at cryogenic temperatures. Also, it can be so made as to control independently contact forces at each stage of the cryocooler cold head.
  • An embodiment of the cryocooler cools a magnet, e.g. a superconductive magnet.
  • the magnet may be for use in magnetic resonance apparatus.
  • a cryocooler cold head receptacle 11 is shown attached to a cryostat 13.
  • the receptacle comprises an inner sleeve 15 which is closed at one end.
  • the closed end extends through an opening in the cryostat and rests on a support in the cryostat.
  • the support comprises a copper enclosed winding form 17.
  • the winding form is supported from the outer cryostat housing by a suspension (not shown).
  • the inner sleeve 15 is fabricated in several sections.
  • the closed end comprises a single piece of copper having first and second diameter cylinders 21a and 21b, respectively, each with its center lying on the same axial centerline.
  • the smaller diameter portion 21b of the cylinder is airtightly secured to the sleeve 15.
  • the copper cylinder is oven brazed in a hydrogen atmosphere to one end of the stainless steel sleeve 15 to form an airtight connection.
  • the larger diameter cylinder 21a is bolted through the copper shield 23 of the winding form 17.
  • a stainless steel bellows section 25 is joined between section 27 and section 29 of the inner sleeve by means of stainless steel bands 31 which are welded in place over the ends of the bellows 25 and the ends of the two sections 27 and 29.
  • Section 29 is brazed to the inner perimeter of a copper ring shaped first stage heat exchanger 35 which forms a portion of the sleeve wall.
  • the exterior of the ring 35 has six equally spaced flats.
  • the upper portion of the sleeve 37 is joined to the outer diameter of the ring 35 creating a circular face 41 inside the sleeve visible in Figure 2.
  • the circular face has two slots 45 to allow flow communication between the upper and lower portions of the inner sleeve 15.
  • the upper portion of the sleeve 37 terminates in the inner perimeter of a first stainless steel flange 47 having a central aperture.
  • the outer 51 and inner sleeves 15 together with the first flange 47 make an airtight seal of the cryostat opening.
  • a split collar 61 fits in a groove in the cryostat and engages the periphery of the first flange 47 when the sleeve compresses axially towards the cryostat.
  • the split collar 61 is shown surrounding the outer sleeve 51 but can alternatively be positioned between the inner and outer sleeves 51 and 15, respectively.
  • a second flange 63 having a central aperture is situated inside the aperture of the first flange 47 with an "O" ring 65 allowing an airtight axially sliding fit.
  • a flange 67 on cryocooler 71 is secured to the second flange 63 with the cold end of the cryocooler including the two cooling stages 73 and 75 extending into the inner sleeve 15.
  • the two stages operate at two different temperatures below room temperature with the second stage being colder than the first stage 73. The exact temperature at the stages depend upon the heat load imposed, but the heat stations typically operate at 50K and 10K, respectively.
  • the two stages 73 and 75 of the cryocooler cold end each have a generally cylindrical shape and lie along the same axial axis.
  • the second stage 75 has a smaller diameter than the first stage and extends therefrom first.
  • the first stage 73 terminates in a disk shaped heat exchanger 77 having a central aperture through which the second stage extends.
  • the second stage terminates in a disk shaped heat exchanger 79.
  • the second stage end of the cryocooler contacts the copper cylinder 21b which closes off the end of the inner sleeve 15.
  • a thin sheet 81 of indium assures good thermal contact between disc 79 and cylinder 21b.
  • An "O" ring 83 is provided between the cryocooler flange 63 and the second flange 67 to assure a hermetic seal so that the inner sleeve 15 can be evacuated when the cryocooler 71 is in place.
  • Adjustment means are provided to move the second flange axially relative to the first flange.
  • a ring of bolts 85 with Belleville washers 87 are shown joining the first and second flanges 63 and 47.
  • the washers 87 are selected to flatten at a predetermined pressure. Tightening the bolts 85 until the washers 87 flatten exert a predetermined force between the flanges.
  • hydraulic clamp means (not shown) can be used to move the flanges axially relative to one another with a predetermined fluid pressure in the hydraulic line resulting in a predetermined force being exerted.
  • the length of the inner sleeve 15 and the cold end of the cryocooler are such that the distance the second flange 63 can move towards the first flange 47 is greater than the space between the first stage heat exchanger 77 of the cryocooler and the surface on the ring 41 against which it seats.
  • a collar 93 of low emissivity material such as copper extends from the shield and surrounds the second stage portion of the inner sleeve 15 which encloses heat station 75 of the cryocooler reducing radiation losses between the 10K cooled surfaces and the cryostat housing 13.
  • the collar 93 is affixed to ring 35, which operates as a first stage interface heat exchanger, by six pieces of copper braid 95 circumferentially spaced about the collar and welded thereto. The other ends of each of the braids extend to separate blocks 97 to which they are welded. The blocks are bolted to the flats on the perimeter of heat exchanger ring 35.
  • the braid 95 permits movement between the inner sleeve 15 and the collar 93 which occurs due to thermal contraction and due to loosening and tightening of bolts 85.
  • Heat transfer between the second stage cryocooler heat station and the shield 23 directly surrounding the coil form having magnet windings 101 is accomplished by copper cylinder 21a being directly bolted to the copper shield 23.
  • the cylinder 21b which closes the end of the inner sleeve is formed from the same piece of copper as the portion which is bolted to the shield 23.
  • Thin indium sheet 81 visible in Figure 2 is situated between the end of the cryocooler second stage heat station and the end of the cylinder 21b assures good heat transfer.
  • Permanently attached resistive leads 103 and 105 extend from the outside of the interface through insulated fittings 106 on the first flange to the interior of the second sleeve 51. The penetration is made airtight.
  • the incoming leads are affixed to tabs 107 extending from two semicircular copper buses 111 and 113, most easily seen in Figures 2 and 3. Tabs 107 extend radially from either end of each of the semicircular buses.
  • the semicircular buses 111 and 113 are bolted to the bottom of the heat exchanger ring 35 together with electrical insulators 115 and 116 separating the copper buses 111 and 113 and the ring, another electrical insulator 117 and a stainless steel ring 121 spreading the load of bolts 123.
  • a layer of indium 125 is situated on either side of insulator 115 to assure a good thermal joint.
  • Insulator 115 comprises alumina or beryllia ceramic. Beryllia is preferred because of its greater heat conductivity.
  • the insulator 115 can be used without any metallization. Alternatively, if the ceramic is metallized with copper or nickel on both sides, the metallized ceramic can be soldered between copper ring 25 and bus bars using a solder with a modulus of elasticity such as indium solder and a pressure joint is not required.
  • the metallization can be applied by vapor deposition.
  • the thickness of the metallization can be 1 mil or less. The ceramic separates the copper or nickel on both sides maintaining electrical isolation between the two surfaces. Typical thicknesses are about 30 mils for the ceramic and 5 mils for the directly bonded metal.
  • the ceramic is not soldered, and bolts 123 extend through insulating sleeves to avoid electrically short circuiting the two semicircular copper buses together.
  • the bolts are tightened to provide at least 2 MPa (300 psi) between layers so that the indium layers 125 flow to assure good thermal conductivity between adjacent faces.
  • a second pair of leads 127 and 129 are soldered to the two remaining tabs 107 on each of the semicircular bus bars so that lead 127 is soldered to the same bus bar as lead 105 and lead 129 is soldered to the same bus bar as lead 103.
  • Leads 127 and 129 are then connected to bus bars 131 and 133, respectively, which are situated in a slot in the cylinder 21a.
  • the bus bars are bolted up into cylinder 21a.
  • a ceramic insulator comprising beryllia or alumina ceramic with two thin sheets of indium on either side are placed between the bus bar and the cylinder.
  • a stainless steel bar on each bus bar spreads the load of the bolts.
  • the bolts create at least 2 MPa (300 psi) between layers to allow the indium to flow to create a good thermal joint.
  • the bus bars are separated from one another a distance sufficient to provide a 250 volt dielectric strength.
  • the bus bars 131 and 133 are joined to the copper bus bars 141 and 143 on the magnet by a bolted joint.
  • a 77K thermal conductance using joints of beryllia and alumina has been measured to be as good as 5 W/cm2-K. Dielectric strength for these ceramics is better than the 250 volts required.
  • the high temperature lead sections will expel 2.3 watts into the first stage of the cooler.
  • the area available for heat transfer here is 12 square cm.
  • the proposed joint design fulfills this requirement.
  • the same magnet design has a heat input to the magnet independent of the current leads of 0.4 W, and an area available for heat transfer from the magnet to the second stage of the cooler of 35 square cm.
  • the best thermal conductance available at 77 K is about 1.8 W/cm2-K. Therefore, assuming this value to be temperature independent, the temperature difference across this joint is 0.0063 K. Now the heat leak down each resistive current lead is 0.31 watts. With the ceramic joint thermal conductance of 5 W/cm2-K, only 9.8 square cm. of area will maintain the temperature rise across this joint at less than 0.0063 K. This much area is available, so the heat will indeed travel into the cooler rather than the magnet.
  • the interface can be installed in the cryostat by first welding the outer sleeve 51 to the cryostat opening with the outer sleeve welded to flange 47.
  • the inner sleeve 15 is installed in the opening by first bolting the copper cylinder 21a to the magnet winding form 17 with the bus bars 131 and 133 already in place. Leads 127 and 129 are soldered in place.
  • the shield collar 93 with the braided sections 95 welded to the collar and blocks 97 is bolted to shield 91. Leads 103 and 105 which pass through flange 47 are soldered to tabs 107.
  • the cryostat 13 is evacuated causing the outer sleeve 51 to contract axially with the first flange 47 supported by the split collar 61.
  • the cold end of the cryocooler is inserted into the inner sleeve 15 and bolted to the second flange 63.
  • the inner sleeve 15 is evacuated creating an atmospheric pneumatic force proportional to the diameter of "O" ring 65 exerted on the second stage cryocooler heat station 75 and the end of the copper cylinder 21b.
  • "O" ring 65 has a 127 mm (5 inch) diameter, for example, the resulting pressure is 0.924 MPa (134 psi) between the second stage cryocooler heat station and copper cylinder 21b.
  • interface pressures may be adjusted by varying the diameter of the outer bellows 53 or "O" ring 65 and by varying spring constants of either or both bellows 25 and 53.
  • cryocooler cold head interface receptacle which makes reliable contacts with low thermal resistance at cryogenic temperatures. Also, the contact forces at each stage of the cryocooler interface can be independently controlled.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Physics & Mathematics (AREA)
  • Mechanical Engineering (AREA)
  • Thermal Sciences (AREA)
  • General Engineering & Computer Science (AREA)
  • Magnetic Resonance Imaging Apparatus (AREA)
  • Containers, Films, And Cooling For Superconductive Devices (AREA)
EP89306786A 1988-07-05 1989-07-04 Coupling a cryogenic cooler to a body to be cooled Expired - Lifetime EP0350266B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US21511488A 1988-07-05 1988-07-05
US215114 1988-07-05

Publications (3)

Publication Number Publication Date
EP0350266A2 EP0350266A2 (en) 1990-01-10
EP0350266A3 EP0350266A3 (en) 1991-01-23
EP0350266B1 true EP0350266B1 (en) 1993-07-21

Family

ID=22801714

Family Applications (1)

Application Number Title Priority Date Filing Date
EP89306786A Expired - Lifetime EP0350266B1 (en) 1988-07-05 1989-07-04 Coupling a cryogenic cooler to a body to be cooled

Country Status (4)

Country Link
EP (1) EP0350266B1 (enrdf_load_stackoverflow)
JP (1) JPH02125601A (enrdf_load_stackoverflow)
DE (1) DE68907654D1 (enrdf_load_stackoverflow)
IL (1) IL90668A (enrdf_load_stackoverflow)

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE19533555A1 (de) * 1995-09-11 1997-03-13 Siemens Ag Vorrichtung zur indirekten Kühlung einer elektrischen Einrichtung
JPH10275719A (ja) * 1997-03-31 1998-10-13 Sumitomo Electric Ind Ltd 超電導体の冷却方法
JP4788050B2 (ja) * 2001-03-14 2011-10-05 アイシン精機株式会社 磁場装置
GB0408425D0 (en) * 2004-04-15 2004-05-19 Oxford Instr Superconductivity Cooling apparatus

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2125767A5 (en) * 1971-02-19 1972-09-29 Comp Generale Electricite Low temp storage appts - with improved means for (un)loading specimens
US4516404A (en) * 1984-03-30 1985-05-14 General Electric Company Foam filled insert for horizontal cryostat penetrations
JPH0629635Y2 (ja) * 1986-09-09 1994-08-10 古河電気工業株式会社 低温保持装置

Also Published As

Publication number Publication date
JPH02125601A (ja) 1990-05-14
DE68907654D1 (de) 1993-08-26
JPH0335811B2 (enrdf_load_stackoverflow) 1991-05-29
EP0350266A2 (en) 1990-01-10
EP0350266A3 (en) 1991-01-23
IL90668A0 (en) 1990-01-18
IL90668A (en) 1992-07-15

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