U.S. patent application number 13/311125 was filed with the patent office on 2012-03-29 for cryogenic vacuum break thermal coupler.
This patent application is currently assigned to Massachusetts Institute of Technology. Invention is credited to Valery Fishman, Alexey L. Radovinsky, Alexander Zhukovsky.
Application Number | 20120073310 13/311125 |
Document ID | / |
Family ID | 39358522 |
Filed Date | 2012-03-29 |
United States Patent
Application |
20120073310 |
Kind Code |
A1 |
Radovinsky; Alexey L. ; et
al. |
March 29, 2012 |
CRYOGENIC VACUUM BREAK THERMAL COUPLER
Abstract
A novel thermal coupler apparatus and method to couple a
cryocooler or another cooling device to a superconducting magnet or
cooled object allows for replacement without a need to break the
cryostat vacuum or to warm up the superconducting magnet or other
cooled object. A method uses a pneumatic actuator for coupling, and
a retractable mechanical actuator for uncoupling. Mechanical
closing forces are balanced between the intermediate temperature
and low temperature cooling surfaces and do not transfer to the
cooled object. The pneumatic actuator provides permanent control
under mechanical closing forces in the thermal coupling.
Inventors: |
Radovinsky; Alexey L.;
(Cambridge, MA) ; Zhukovsky; Alexander; (Brighton,
MA) ; Fishman; Valery; (Framingham, MA) |
Assignee: |
Massachusetts Institute of
Technology
Cambridge
MA
|
Family ID: |
39358522 |
Appl. No.: |
13/311125 |
Filed: |
December 5, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11881990 |
Jul 30, 2007 |
8069675 |
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13311125 |
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60850565 |
Oct 10, 2006 |
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Current U.S.
Class: |
62/6 |
Current CPC
Class: |
F25D 19/006
20130101 |
Class at
Publication: |
62/6 |
International
Class: |
F25B 9/00 20060101
F25B009/00 |
Claims
1. A coupler for thermally coupling a cooling device having at
least one cooling stage, to an object to be cooled, the coupler
comprising: a. a cold station configured to couple with a cold
stage of a cooling device and configured to connect with an object
to be cooled; b. mechanically rigidly connected to the cold
station, an actuator support, between which and the cold station,
the cold stage of the cooling device fits, movably; c. a coupling
actuator arranged to apply substantially equal and opposite forces
to the cold stage and the actuator support, thereby forcing the
cold stage from an uncoupled configuration into a coupled
configuration, with the cold stage contacting the cold station,
without any force being applied to the object to be cooled; d. a
cooling device vacuum enclosure shaped and sized to house a cooling
device vacuum around the cooling device, comprising the cold
station; and e. a cooled object vacuum enclosure, shaped and sized
to house an object to be cooled, comprising the cold station,
arranged to house a cooled object vacuum that is hydraulically
independent from the cooling device vacuum.
2. The coupler of claim 1, further wherein the cold stage contacts
the cold station without any force being applied to the cooling
device.
3. The coupler of claim 1, further wherein the cold stage contacts
the cold station without any force being applied to the cooling
device vacuum enclosure.
4. The coupler of claim 1, further wherein the cold stage contacts
the cold station without any force being applied to the cooled
object vacuum enclosure.
5. The coupler of claim 1, further wherein the cold station is
configured to connect fixedly with an object to be cooled.
6. The coupler of claim 1, further comprising, thermally coupled to
the cold stage, an indium gasket.
7. The coupler of claim 1, the actuator comprising a pneumatic
actuator.
8. The coupler of claim 7, the pneumatic actuator comprising a
plurality of pneumatic actuators, arranged to operate in
parallel.
9. The coupler of claim 7, the pneumatic actuator comprising a
plurality of pneumatic bellows, arranged to operate in
parallel.
10. The coupler of claim 1, the actuator support comprising a
surface arranged substantially facing and opposite the cold
station, the actuator comprising a linearly extendible member,
coupled to the actuator support surface and pushing the cold stage
of the cooling device, toward the cold station, upon
energization.
11. The coupler of claim 1, further comprising a releasable couple
that releasably couples the cold stage with the coupler.
12. The coupler of claim 11, the cold stage comprising a device
circumferential flange, the releasable couple comprising a coupler
circumferential flange, connected to the cold station, the device
flange and the coupler flange being shaped and arranged so that: a.
with the cooling device in a first rotational position, translation
of the cold stage relative to the coupler is limited to a range of
inserted positions; and b. with the cooling device in a second
rotational position, translation of the cold stage relative to the
coupler is free to move beyond the range of inserted positions.
13. The coupler of claim 11, the releasable couple comprising a
clutch.
14. The coupler of claim 1, the cooling device comprising a
cryocooler.
15. The coupler of claim 1, the object to be cooled comprising a
magnet.
16. The coupler of claim 7, the pneumatic actuator comprising an
actuator that uses helium gas as a source of actuation.
17. The coupler of claim 1, further comprising: a. an object to be
cooled; and b. an apparatus coupled functionally to the object to
be cooled.
18. The coupler of claim 17, the object to be cooled comprising a
magnet.
19. The coupler of claim 17, the apparatus coupled functionally to
the object to be cooled comprising a magnetic resonance imaging
apparatus.
20. The coupler of claim 1, further comprising a cooling
device.
21. The coupler of claim 20, the cooling device comprising a
cryocooler.
22. The coupler of claim 1, further comprising a retraction
actuator, coupled to the cold stage, which retraction actuator is a
different actuator from the coupling actuator, the retraction
actuator arranged to move the cold stage from the coupled position
to an uncoupled position.
23-45. (canceled)
46. A method to thermally couple a cooling device having at least
one cooling stage to an object to be cooled, the method comprising
the steps of: a. providing a thermal coupler comprising: i. a cold
station connected with the object to be cooled and configured to
couple, with a cold stage of the cooling device; ii. mechanically
rigidly connected to the cold station, an actuator support, between
which and the cold station, the cold stage fits, movably; iii.
connected to the cold stage, at least one wing extension configured
to fit through at least one corresponding opening in the actuator
support; iv. an engagement actuator arranged to apply substantially
equal and opposite forces to the at least one wing extension of the
cold stage and the actuator support, upon energization, thereby
forcing the cold stage from an uncoupled position, toward and into
a coupled position, contacting the cold station, without any force
being applied to the object to be cooled; v. a cooling device
vacuum enclosure shaped and sized to house a cooling device vacuum,
around the cooling device, comprising the cold station; and vi. a
cooled object vacuum enclosure, shaped and sized to house an object
to be cooled, arranged to house a cooled object vacuum that is
hydraulically independent from the cooling device vacuum; b.
introducing the cooling device into the cooling device vacuum
enclosure, such that the at least one wing extension passes through
the corresponding opening in the actuator support and positioning
the cold stage of the cooling device in an uncoupled position
between the actuator support and the cold station; c. rotating the
cooling device so that the at least one wing extension is opposite
the actuator; and d. energizing the actuator, so that it engages
the wing extension, thereby forcing the cold stage from an
uncoupled position, toward a coupled position, contacting the cold
station, without any force being applied to the object to be
cooled.
47. The method to couple of claim 46, the actuator comprising a
pneumatic actuator, the step of energizing the actuator comprising
increasing the pressure of a gas provided to the actuator.
48. The method of claim 46, the step of providing a thermal coupler
further comprising, providing an indium gasket, bonded to the cold
stage.
49. The method of claim 46, the actuator comprising a pneumatic
actuator, the step of energizing the actuator comprising increasing
the pressure of helium gas provided to the actuator.
50. The method to couple of claim 46, further comprising the step
of establishing a vacuum within the cooling device vacuum
enclosure.
51. The method to couple of claim 46, further comprising the step
of activating the cooling device.
52. The method to couple of claim 51, the step of activating the
cooling device taking place before the step of energizing the
actuator.
53. The method to couple of claim 51, the step of activating the
cooling device taking place after the step of energizing the
actuator.
54. The method to couple of claim 46, the step of providing a
coupler comprising the step of providing a retraction actuator,
coupled to the cold stage, which retraction actuator is a different
actuator from the coupling actuator, the method to couple further
comprising the step of energizing the retraction actuator to move
the cold stage from the coupled position to an uncoupled
position
55-62. (canceled)
Description
RELATED DOCUMENTS
[0001] The benefit of U.S. Provisional application No. 60/850,565,
filed on Oct. 10, 2006, entitled CRYOGENIC VACUUM BREAK PNEUMATIC
THERMAL COUPLER, is hereby claimed, and the entire document is
hereby incorporated by reference herein.
BACKGROUND
[0002] The progress of cryocoolers in the past 20 years has brought
the technology to the state where magnet cooling in the absence of
liquid cryogens is a more attractive option than with the use of
liquid helium for some applications. In addition to cost and
convenience, the absence of liquid helium is attractive from the
point of safety, as the issues with rapid pressurization of the
cryogen and possible release of helium gas to environment
surrounding the device can be avoided. Cryogen-liquid-free magnets
require fewer external subsystems, fewer services, and thus are
also more portable.
[0003] Many applications of the cryogen-free technology have been
implemented, from magnets to detectors, for applications in outer
space as well as on the ground.
[0004] The present liquid-free cryocooler technology is very
reliable, with present Mean-Time-Between-Failures of about 10000
hours for Gifford-McMahon cryocoolers and 20000 hours for
pulse-tube cryocoolers. Although adequate for short-term
applications, for long term application means of being able to
replace the unit for maintenance are necessary.
[0005] Usual thermal insulation for the cooled object and for the
cryocooler cold head includes vacuum isolation of the cold
surfaces. Apiezon N grease is used in couplings for a better
thermal contact and improved thermal conductivity at cryogenic
temperatures in vacuum. In demountable (those that need to be
disconnected) couplings, indium gaskets are used for the same
purpose. Indium gaskets compressed in the coupling with a pressure
at which indium flows plastically provide a good thermal contact in
the connected couplings, with reliable demountable joints.
[0006] For some long-term applications, it is desirable to replace
the head of the cryocooler without breaking the cryostat vacuum
around the cold object, and sometimes even without warming up the
device. The need for removing the cryocooler head, without cooled
device warm-up, demands features of both the thermal management
system as well as for the vacuum that surrounds the cooled magnet.
It is a purpose of an invention hereof for a mechanical and thermal
coupler and a method of providing a quick thermal and mechanical
connect and disconnect of a cryocooler, which does not require
warm-up of the cooled device while replacing a cryocooler, which
can be performed quickly without influencing the cooled object
vacuum, and which can be conducted without any forces being applied
to the object to be cooled, which is generally sensitive thereto.
It is also important, where possible, to provide for such quick
thermal and mechanical connect and disconnect of a cryocooler
without applying any force to any of: the cooling device itself,
the walls of the cooling device vacuum or the walls of the cooled
object vacuum. For better thermal coupling, the coupler should also
provide reliable and controllable contact pressure between the
cryocooler cold head and the cooled object thermal stations through
the coupler of the demountable thermal joints.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1A shows a schematic cross-section view of a partially
axially symmetric pneumatically actuated coupler for providing
thermal contact between a two-stage cryocooler and corresponding
cooled object, with both stages engaged;
[0008] FIG. 1B shows a cross-sectional view of the coupler shown in
FIG. 1A, with both stages of the cryocooler disengaged from the
cooled object and the intermediate temperature thermal path;
[0009] FIG. 2 shows a schematic of a pneumatic actuator;
[0010] FIG. 3 shows a cross section view of a coupler between the
cryocooler first stage and the intermediate temperature station,
showing a mating wing and flange arrangement for installation and
removal of the cryocooler (in a disengaged position);
[0011] FIG. 4A shows an enlarged view of a portion of the
cross-section view of FIG. 1A, showing the cryocooler engaged to
the cold thermal path to the cooled object (magnet);
[0012] FIG. 4B shows an enlarged view of a portion of the
cross-section view of FIG. 1B, with cryocooler disengaged and gap
36 open;
[0013] FIG. 5A shows an enlarged view of a portion of the
cross-section view of FIG. 1A, showing the intermediate temperature
thermal path with cryocooler engaged;
[0014] FIG. 5B shows an enlarged view of a portion of the
cross-section view of FIG. 1B, with cryocooler disengaged and gap
38 open;
[0015] FIG. 6A is a schematic representation in cross-sectional
view of a generic cooling device having only one stage, and a
coupler and cooled object, shown in a disengaged configuration with
gap 136 open;
[0016] FIG. 6B is a schematic representation of the apparatus shown
in FIG. 6A, shown in an engaged configuration; and
[0017] FIG. 7 is a schematic representation of a portion of the
apparatus shown in FIG. 6A, in partial end view along the lines
7-7, with the cooling device retracted and rotated from the
position shown in FIG. 6A.
SUMMARY
[0018] A more detailed partial summary is provided below, preceding
the claims. Coupler systems are described herein to provide for a
quick thermal and mechanical connect and disconnect of cryocooler
heads. Two vacuums are used. The vacuum that is used in the
cryocooler environment is different from that of the cooled object
vacuum (cryostat vacuum). Mechanical means apply the required
forces to maintain good contact between discrete components, to
effectively transfer thermal loads in vacuum. For a two stage
cooling device the actuator creates adjustable forces on interfaces
between the cryocooler stages and respective thermal stations of
the cooled object. Forces at the interfaces are reacted through the
actuator in series with the walls separating the cryocooler and
cryostat vacuums.
[0019] In addition, it is convenient to provide the pressures
required for establishing good thermal contact across the interface
of the demountable thermal joints in vacuum by means that do not
transfer loads to the object to be cooled. Surfaces designed with
compressible gaskets for good thermal transfer across the interface
may bond, so that breaking the demountable thermal joint is
difficult. Means are disclosed to provide the forces required for
separation of different elements in the interface.
DETAILED DESCRIPTION
[0020] FIGS. 1A and 1B show a coupler system where there are two
separate vacuums for a cooled object and for the cryocooler, as
well as two thermal paths for the cooled object (cold thermal path)
and intermediate temperature thermal path (for the radiation
shield, current leads and others).
[0021] FIG. 1A is a cross-section through an embodiment of an
apparatus invention hereof, showing the cooling device engaged.
FIG. 1B is a cross-section through the apparatus, showing the
cooling device disengaged. FIG. 1A shows the cryocooler engaged to
both the intermediate temperature and cold thermal stations. FIG.
1B shows the cryocooler disengaged from the intermediate
temperature and cold thermal stations. (In the industry, typically
the warmer temperature station is referred to as the intermediate
thermal station (being intermediate between cold and room
temperature). As used herein, and in the claims, either the term
first, or the term intermediate may be used to identify a thermal
station, that is typically not the coldest station. In the claims,
typically first is used, whereas in this specification,
intermediate is typically used.) The word station is generally used
to refer to a component permanently thermally connected with the
cold object or its radiation shield. Below, the word stage is
generally used to refer to a component of the cooling device.
[0022] The object to be cooled and its surrounding cryostat are not
shown in FIG. 1A or 1B, because to do so and show both to scale is
awkward. Typically, the object to be cooled is significantly larger
in both mass and dimensions than the cryocooler. For instance, the
mass of a cryocooler could be 10 kg, to cool a magnet of about 1000
kg. The relative physical dimensions would be similarly sized.
[0023] The cooled object external vacuum boundary, between the
outer environment and the cooled object vacuum includes the
cryostat vacuum wall 28, bellows 32 and room temperature flange 23,
end other elements not shown. There is an internal boundary between
the cooling device vacuum and the cooled object vacuum established
by the cryocooler sleeve, including the cold station 30,
cold-to-intermediate temperature support tube 12, intermediate
temperature flange 14 and intermediate-to-room temperature support
tube 24, attached to the room temperature flange 23.
[0024] The cooling device vacuum is bounded, on its inside, by the
cooling device itself, having first stage 4 and second stage 6, and
on its outside some elements that bound, in part, the cold object
vacuum, including cold station 30, cold-to-intermediate support
tube 12, intermediate temperature flange 14, intermediate-to-room
temperature support tube 24, room temperature flange 23, and
flexible bellows 44, end vacuum flange 46 and cryocooler head
flange 2.
[0025] There are two thermal paths. The cold thermal path includes
the cryocooler second stage 6 through cold station 30 and cold
thermal anchor 10. The cold thermal anchor 10 is in good thermal
contact with the cooled object, not shown. The means by which the
cooled object is thermally and mechanically connected to the cold
anchor are not important, except that the connection is of a type
that does not result in any forces being applied to the object to
be cooled as a result of establishment of the thermal coupling with
the cooling device into the thermal paths, described below.
Typically, the cold station 30 and the cold anchor 10 are fixed to
each other, essentially permanently, for example, by bolts, or any
other suitable mechanism to establish a permanent thermal
connection. Thus, they may be considered together as a cold unit
60. In fact, rather than the two separate elements of a cold anchor
10 and a cold station 30 being used, a single unitary cold unit 60
may be used in some circumstances. The term cold unit is used in
this specification and the attached claims to mean both the two
separate elements of a cold anchor 10 and a cold station 30
associated together, or a single unitary element that performs
their functions.
[0026] To increase thermal conductance, a pliable layer can be
placed between the surfaces in thermal joints. For instance,
Apiezon N grease can be used in the coupling for better thermal
contact between cold station 30 and cold thermal anchor 10, which
is not disturbed during cryocooler removal/installation. Indium
gasket 48 is bonded to the surface of the cryocooler cold stage 6
that is in contact with the cold station 30 (see FIGS. 4A and 4B).
The cold thermal circuit is broken by retracting the cryocooler and
opening a gap 36 between the cryocooler second stage 6 and the cold
station 30. During disengagement and removal, indium gasket 48
remains attached to cryocooler second stage 6. (In the industry for
two stage cryocoolers, typically, the warmer temperature stage is
referred as the first stage, which is used to cool the intermediate
temperature thermal station (being intermediate between cold and
room temperatures). The second stage refers to the coldest
temperature stage of the cryocooler, which is used to cool the
cooled object.)
[0027] The intermediate temperature thermal path includes the
cryocooler first stage 4, cryocooler first stage wing 16, the
intermediate temperature station 18, flexible thermal anchor 26,
intermediate temperature flange 14, and the intermediate
temperature flexible thermal anchor 8, which is in good thermal
contact with the intermediate temperature thermal shield. The
intermediate temperature thermal shield surrounds the cooled object
and serves to intercept the heat to the cold object as well as to
the current leads, cold mass supports, and other sources of heat at
temperatures between the cooled object and room temperature. The
intermediate temperature thermal path is interrupted when the
cryocooler is retracted, opening a gap 38 in the intermediate
temperature thermal path between the intermediate temperature
station 18 and cryocooler first stage wing 16. The indium gasket 54
is attached to the cryocooler first stage wings 16, and is removed
with it during cryocooler retraction.
[0028] An actuator includes a deformable element 20 (for instance
bellows) that is filled with gas that does not liquefy or solidify
at the operating temperature (for instance helium) through
pneumatic actuator pressurization tube 40 (see FIG. 2). When the
actuator is not pressurized, it assumes an uncoupled position,
which corresponds to the stages of the cooling device being
uncoupled mechanically and thermally from the intermediate and cold
temperature stations, and thus, the object to be cooled. When the
actuator is powered to expand, by being pressurized, the bellows
expands, and equal and opposite forces are applied to intermediate
temperature station 18 and to pneumatic actuator support 22.
[0029] Retracting actuator 34 is shown as a linear motion actuator,
which can be displaced in the same direction as the main axis C of
the cryocooler. It has access to the cryocooler space vacuum
through flexible retracting actuator bellows 58, which permits
axial displacement of the retracting actuator 34 for cryocooler
disengagement without breaking vacuum. The retraction limiter 52 is
immobile, and contacts the cryocooler first stage wing 16 during
retraction of the cryocooler, to provide the force necessary to
open the gap 38 in the intermediate temperature thermal path and
gap 36 in the cold path.
[0030] A pneumatic bellows 20 is attached at one end to the
pneumatic actuator support 22 with another end facing the
intermediate temperature station 18 (see FIG. 2). The retracting
limiter 52 is placed between actuator bellows and under the wings
of the pneumatic actuator support 22 and intermediate temperature
station 18.
[0031] A purpose of an invention hereof is to provide means for
attaching a cryocooler with two stages to an intermediate
temperature station and a cold station of a cooled object in such a
manner as to enable quick connect and disconnect, without applying
any forces to the object to be cooled due to the thermal coupling
or uncoupling with the cooling device. This operation is required
for cryocooler head replacement, both for regular maintenance as
well as for unscheduled maintenance, without the need to break the
cooled object vacuum or to warm up the thermal radiation shield,
current leads and cooled object. The cooled object can be a
superconducting magnet, a detector, a motor or other cooled device,
while the intermediate thermal station can be thermally connected
to current leads, and/or to a thermal radiation shield, and/or to
mechanical supports of the cooled object to minimize a heat load of
the cooled object.
[0032] As an example, not to be taken as limiting, of a useful
embodiment, the intermediate temperature is between 25 and 90K,
while the cooled object can be from 2 K all the way to 30 K. For
applications with low temperature superconducting magnets the
intermediate temperature can be around 40-70 K, while the
temperature of the cooled object (superconducting magnet) is from 3
K to 12 K.
[0033] An engagement sequence is described next (see FIGS. 1A and
1B). First the retracting actuator 34 is reset to allow engagement
by the pneumatic actuator bellows 20. After the cryocooler is
placed so that the cryocooler first stage wings 16 go through the
slots in pneumatic actuator support 22 and intermediate temperature
station 18, the cryocooler is rotated until the wings 16 of the
cryocooler first stage are placed directly between the intermediate
temperature station 18 and the retractor ring 56. The vacuum flange
46 of the cryocooler head 2 is sealed to seal the cryocooler vacuum
(bounded as described above). The space of the cryocooler vacuum is
pumped out.
[0034] The actuator is, at this moment, in an uncoupled position.
Engagement is then carried out by increasing the pressure of the
helium gas in the pneumatic actuator bellows 20 by feeding gas
through pneumatic actuator pressurization tube 42, and the
pneumatic actuator bellows 20 extends to a coupling position,
exerting a force to intermediate temperature station 18 and an
equal and opposite force to the pneumatic actuator support 22. The
intermediate temperature station moves (due to a flexible
connection 26 with flange 14), closing the gap 38 in the
intermediate temperature path. The force on the intermediate
station 18 is transmitted to the wings 16 attached to the first
stage 4 of the cryocooler and through its rigid body to the cold,
second stage 6, pushing it toward the cold station 30 (to the
right, as shown), and closing the gap 36. The balancing force
(toward the left, as shown) on the pneumatic actuator support 22 is
transmitted through the rigidly connected intermediate-to-room
temperature support tube 24, intermediate temperature flange 14,
cold-to-intermediate support tube 12 and cold station 30. Once the
gaps 36 and 38 close, the cryocooler 4, 6 stages are pinched
between the intermediate temperature station 18 and the cold
station 30, with the pressures at the interfaces which were
formerly the gaps 36 and 38, increasing as pressure in the actuator
20 increases.
[0035] Once the actuator is in the coupling position and the gaps
are closed, the actuator continues to apply increasing forces on
the contacting elements, which increasing forces are reacted along
the cryocooler cold head 6, cryocooler body between two stages, and
first stage head 4, establishing good thermal coupling in thermal
pathways.
[0036] No force is transferred or applied to the cold object (and
its radiation shield) when the cryocooler is compressed against the
thermal stations of the cold object and its radiation shield. This
condition can be achieved if the heat transferring surfaces 16* of
the first and 6* of the second stages of the cryocooler, face in
opposite directions.
[0037] This is facilitated by the first stage 4 of the cryocooler
having wings 16, which penetrate through respective openings in the
intermediate temperature station 18.
[0038] During initial installation and during replacements when the
cold object has been allowed to warm up, the cryocooler is turned
on after engaging the intermediate temperature thermal path and the
cold thermal path and energizing the actuator.
[0039] In the case of the cold object remaining at cold
temperatures, there are at least two options for starting up the
cryocooler. One method has the cryocooler turned on and allowed to
partially cool before activating (pressurizing) the pneumatic
actuator bellows 20 and connecting the cryocooler to the
intermediate temperature and the cold temperature thermal paths.
Alternatively, in another method the pneumatic actuator bellows 20
is activated, establishing contact between the warm cryocooler and
the colder intermediate temperature station 18 and cold station 30.
After the gaps are closed and the intermediate temperature and cold
thermal circuits are reestablished, the cryocooler is turned
on.
[0040] The same but opposite directed forces act on the surface of
the cold station 30 and the surface of the intermediate temperature
station 18, across which the cold thermal path and intermediate
temperature thermal path are established. The contact areas at the
intermediate temperature station 18 and cold station 30 are
selected so that appropriate contact pressures are applied at both
stages for adequate thermal transfer. A pliable material, for
instance, an indium gasket 54 in FIG. 2 at the intermediate
temperature thermal path, and indium gasket 48 (see FIGS. 4A and
4B) at the cold temperature thermal path, are placed between mating
surfaces in both the intermediate temperature and the cold thermal
paths to maximize thermal conductance in a vacuum.
[0041] The contact pressure across the intermediate temperature and
cold thermal circuits demountable joints can be adjusted by varying
the pressure of the gas in the pneumatic actuator 20. A beneficial
gas in the bellows is helium. Pneumatic actuators offer a
significant advantage over some other actuators, such as a
mechanical spring actuator, because a pneumatic actuator can
provide precise pressure, and thereby pressure control in the
thermal coupling, even over a very wide range of temperature
variation during the entire time of the cryocooler operation.
[0042] One of the ends of the intermediate-to-room temperature
support tube 24 is at room temperature, on the side of the room
temperature flange 23 and the other end is in contact with the
intermediate temperature flange 14. Similarly, the
cold-to-intermediate temperature support tube 12 is in contact with
the intermediate temperature flange 14 at one end and with the cold
station 30 at the other. To prevent excessive heat loads, the tubes
are made of thin steel, sufficiently thick to support the loads,
but thin enough to maintain low thermal conductance between the
ends. To increase the length of the warm-cold thermal passes along
tubes and reduce heat transfer along the tubes, they can be made as
a reentrant assembly of multiple tubes welded to stainless steel
spacer rings 11, 13, 21 and 25, as shown in the figures.
[0043] When pneumatic actuator 20 is pressurized the cryocooler
body between the first stage 4 and the second stage 6 is in
compression. Structural issues of the cryocooler may limit the
forces applied by the pneumatic actuator 20. If so, a reinforcing
crossbar can be installed between the first and the second stage
flanges of the cryocooler. The reinforcing crossbar may be made of
a material with low thermal conductivity, for instance a
fiber-glass material. Another constraint is the pressure
limitations of the bellows of the pneumatic actuator 20.
[0044] Simply removing the pressure on the gas of the pneumatic
actuator bellows 20 is not enough to disengage the intermediate
temperature and cold stations. Substantial forces need to be
applied to break the mechanical adhesion at the coupling with
indium gaskets. There are multiple means to apply these forces. The
figures show, for example, a retraction actuator 34.
[0045] A cryocooler disengagement and removal method is described
next. If the cold object is a non-persistent superconducting
magnet, the magnet is preferentially de-energized during the
cryocooler replacement operation. The pneumatic actuator 20 is
de-pressurized. Then retraction actuator 34 is used to provide a
force to disengage the cryocooler. Two possible outcomes occur
next, depending on which gap opens first: the gap 38 in the
intermediate thermal path, or gap 36 in the cold path.
[0046] If gap 36 in the cold path opens first, the cryocooler
second stage 6 moves away from the cold station 30. After some
travel away from the cold station 30, the cryocooler first stage
wing 16 contacts the retraction limiter 52. Continued application
of the retraction actuator 34 results in forces applied to
disengage the cryocooler first stage wing 16 from contact with the
intermediate temperature station 18. After gap 38 opens in the
intermediate temperature thermal path, the cryocooler is no longer
thermally or mechanically attached to the system.
[0047] If, instead the gap 38 opens first, then further application
of the retraction actuator 34 moves the intermediate temperature
station 18 away from the cryocooler first stage wing, until
eventually retractor ring 56 contacts the cryocooler first stage
wing 16. Continued application of the retraction actuator 34 would
then disengage the cryocooler second stage 6 from the cold station
30, opening the gap 36 in the cold path. In either case, cryocooler
disengagement can be confirmed by the position of the cryocooler
head and the retraction actuator 34.
[0048] After both gaps 36 in the cold path and 38 in the
intermediate temperature thermal path have opened, the cryocooler
vacuum space (bounded as described above) is filled with helium
gas. The gas (from an external gas source) is introduced in the
cryocooler vacuum space (the gas supply line is not shown in the
Figures), to prevent condensable gases from accessing the
cryocooler vacuum space and condense on cold surfaces. The
cryocooler head 2 is disconnected from the vacuum flange 46 by
removing bolts connecting the cryocooler head 2 to the vacuum
flange 46, while maintaining a steady flow of helium gas to prevent
air from entering the cryocooler vacuum space and condensing on
cold surfaces. The cryocooler is then rotated so that the
cryocooler first stage wings 16 clear the wings in the intermediate
station 18. At this point, the cryocooler is clear and can be
removed. The vacuum flange 46 is sealed by a temporary cover to
prevent air from entering and condensing on cold surfaces.
[0049] Replacement of the cryocooler has been described above, for
both the cold object at near room temperature (during initial
installation or during maintenance where the cold object has been
allowed to be warmed up), and for when the cold object remains at
low temperature.
[0050] To provide good thermal contact in a vacuum between the cold
station 30 and the cold thermal anchor 10, they may be soldered
together or a thin layer of thermal conducting deformable material
may be introduced to the surface before assembly. For instance, a
useful material is Apiezon-N grease. The connection between cold
station 30 and the cold thermal anchor 10 is established by a set
of screws, and is not disconnected during cryocooler retraction and
remains cold during the maintenance operation.
[0051] The demountable contact between the cryocooler cold head 6
and the thermal station 30 is provided by a thin ductile metal that
remains ductile at operating temperatures, such as indium. It is
necessary to remove the indium gaskets during cryocooler removal,
and thus the indium gasket 48 is adhered to the cryocooler second
stage 6. Similarly, the indium gasket 54 is attached to the
cryocooler first stage wing 16, and is removed with the cryocooler
head. Apiezon-N grease is a material used in all cryogenic
non-disconnected thermal couplings to reduce temperature drops in
these joints operating in vacuum.
[0052] The retraction actuator 34 has no contact with the cold
temperature thermal path. The retraction actuator 34 is only in
contact with elements at intermediate temperature, and represents a
small additional thermal load to the cryocooler first stage.
[0053] The bellow actuators 20 present additional heat load to the
first stage of the cryocooler due to thermal conductance from
relatively warm intermediate-to-room temperature support tube 24
and pneumatic actuator support 22 to the intermediate temperature
station 18 and then to the first stage of the cryocooler. This
thermal load is limited by thin walls of low thermal conductivity
stainless steel bellows as well as thermal insulation disks (for
instance of fiberglass composite) bonded to the bottom of the
bellow to avoid metal-to-metal contact with the intermediate
temperature flange 18. Thermal load to the first stage of the
cryocooler due to pneumatic actuator pressurization tube 40 can be
limited by using small diameter (2-3 mm) thin wall tube with a very
big relative length (length/diameter). Thermal convection from the
room temperature region through the pneumatic actuator
pressurization tube 40 and inside pneumatic actuator 20 also could
present additional heat load for the first stage of the cryocooler.
If this thermal load is a problem, the pneumatic actuator
pressurization tube 40 can be provided with multiple internal
porous plugs (for instance made from compressed stainless steel
wires or chips, or high density metallic or ceramic foams) to
strongly limit convection heat load due to gas in tubes.
Additionally a package of several steel foil disks with thin
fiberglass spacers inserted in thermally-insulating tube with
diameter close to the bellow inner diameter and attached to the
cold bottom of the bellows can minimize convection and radiation
thermal load inside the bellows to its cold surface and to the
first stage of the cryocooler. The disks and cylinder have very
small holes, which permit equal pressure inside the bellows as well
as pumping it out.
[0054] During cryocooler replacement, the vacuum of the cryocooler
is broken by filling the space with flowing helium gas (to avoid
condensation and freezing of atmosphere gases and moisture on the
cold surfaces), by introducing helium gas deep in the cryocooler
vacuum space (precise location not shown in the figures). The
presence of helium gas at atmospheric or slightly above its
pressure does represent a thermal load to both intermediate
temperature and cold thermal circuits, but it is possible to
rapidly replace the cryocooler and reestablish the vacuum before
much heating of the intermediate temperature and cold thermal paths
has occurred.
[0055] The cryocooler and coupler can be oriented with the stages
of the cryocooler extending generally horizontally, or vertically,
or at any orientation in between.
[0056] Before engagement, the cryocooler is supported at its head
2, from which the body, including stages 4 and 6 is cantilevered at
a horizontal orientation. If it is necessary, alignment supports
can be provided to support the cantilevered body against tilting
under the force of gravity, or to maintain proper alignment within
the cavity. When engaged, the cryocooler is mechanically supported
at 30 and partially at 18 by friction forces that arise normal to
the compression forces at the interfaces that had formerly been the
gaps 36 and 38. At the warm end the weight load of the cryocooler
head is taken by flange 46, bellows 44, flange 23, bellows 32, the
major cryostat wall 28, and alignment supports. When disengaged,
the cryocooler weight is supported only by flange 46 and other
parts, see above. The large axial forces required to establish the
intermediate temperature and the cold thermal paths are
self-contained and balanced within the elements that experience
them. Vibrations of the cryocooler in the direction normal to the
main axis C of the cryocooler are damped by the presence of
flexible bellows 44 and 32. However, axial vibrations are
transmitted to the cold station 30. If needed to prevent these
vibrations in the cooled object, it is possible to have a section
of the cold thermal anchor 10 that is flexible. Vibrations of the
elements in the intermediate temperature thermal paths are damped
by the flexible thermal anchor 26 and by flex in 8.
[0057] An attractive feature of an invention disclosed herein is
that no forces are transferred or applied during placement,
operation and removal of the cryocooler from the cryocooler to the
cold object or to the thermal shield. The forces needed to
establish good thermal conduction in both the intermediate
temperature thermal path as well as in the cold thermal path are
self-contained. Good thermal contact is positively achieved by
appropriate selection of the contact areas, and by application of
adequate pressure in the pneumatic actuator 20. Good thermal
conduction to the cooled object is achieved by using a rigid cold
thermal anchor 10.
[0058] With or without thermal connection between the cryocooler
and cooled object being established, there are no forces applied to
the cooled object from the cryocooler.
[0059] Forces created by the actuator are contained within the
structural elements including the cryocooler and its stages 4, 6
and the vacuum walls 24, 12, of the cryocooler vacuum. The cold
thermal station is firmly attached to the cold thermal anchor 10
for instance by bolts 35.
[0060] In the example shown, the fixture transduces an actuator's
linear expansion and the equal and opposite forces generated
thereby, to equal and opposite compression forces applied to the
cooling device at its intermediate and cold temperature stages.
Alternative actuation and fixture designs are possible. What is
required is that engagement of the thermal conduction path between
the object to be cooled and the cooling object take place without
any unbalanced forces applied externally to the object to be
cooled. The forces in the thermal coupling are self-contained in
the circuit consisting of part of the cooling device between two
stages, actuator, and vacuum walls of the cooling device. An
alternative design can provide tension forces to the cooling device
between intermediate and cold temperature stages. The actuator need
not be linear, or pneumatic. It may be rotary, linkages,
compressive, etc. It can be electro-mechanical, pneumatic,
hydraulic, etc. In general, as the actuator is powered, the cooling
device is brought to a coupled position with the cold unit 60, and
thus, the object to be cooled. With a linear actuator, it is
powered to expand. Other actuators may be powered to rotate
elements into a coupled position. A pneumatic actuator, powered by
a gas such as helium, does provide the control advantages described
above, in a cryogenic context.
[0061] The foregoing has described a cryocooler having two stages:
a first stage, referred to herein as an intermediate temperature
stage, and a second stage, referred to herein sometimes as a cold
(lowest temperature) stage. Different cooling devices are used for
different applications. The cooling device could be a different
kind of cryocooler, such as a pulse tube, Gifford-McMahon, or
Sterling type, with one or two stages (one or two temperature
levels), cryostats with cryogenic liquid, cryogenic refrigerators
(with one, two, or three levels of cooling temperatures) etc. A
two-stage cryocooler typically has a united cooling system with two
stages (to be connected with the cooled object). It is also
possible for there to be more than two stages. For instance,
cryogenic refrigerators), could have three stages available for
cooling (for instance 78 K, 20 K, 2.0 K). Usually the coldest
temperature is used to cool the cooled object and the higher
temperatures are used to cool thermal shields (one or two) around
the cooled object, current leads, cold mass supports and so on.
Such a cooling scheme decreases power required for cooling.
[0062] Rather than two stages, there may be only one stage. A
single stage set-up is described below, in conjunction with FIGS.
6A and 6B, which show a single stage cooling device and cooled
object, with a quick-release thermal coupler in a disengaged
configuration shown in FIG. 6A, and an engaged (coupled)
configuration shown in FIG. 6B. FIG. 6B only shows a portion of the
device shown in FIG. 6A. FIG. 7 shows a cross-section through the
device shown in FIG. 6A, at lines 7-7. The object to be cooled and
its surrounding cryostat are shown in FIGS. 1A and 1B, not to
scale. Generally they are much bigger than the cooling device.
[0063] A one stage cooling device 102, of any suitable kind,
engages a thermal coupler 119. The coupler, includes an actuator
support 122, a fixture 168, a cold station 130 and actuators 120a,
b, etc., with reference numeral 119 referring to all of these
elements together as a coupler, as discussed below. The cooling
device cold head 106 is thermally conductively secured (such as by
permanent bolts) to a cold head extension 107 with wings made of a
thermal conductive material, which may be, for instance of copper.
A gap 136 is shown between the cold head extension with wings 107
and the stationary cold station 130. The stationary cold station
130 is thermally conductively coupled to the cold object 137
through a cold anchor 162. The cold anchor 162 and cold object 137
are secured to the cold station 130 by a permanent means such as
bolts 135 between a flange 163 and the cold station 130. For a
better heat transfer in vacuum they (cold anchor, flange and cold
station) can be soldered together, connected with application of
indium gasket, or Apiezon N grease.
[0064] As with a two stage device discussed above, the two separate
elements of cold anchor 162 (with its flange 163) and cold station
130 are secured to each other essentially permanently, and thus may
be referred to herein and in the claims as a cold unit 161, or
their functions can be served by a unitary element that is also
referred to herein as a cold unit.
[0065] An actuator has a plurality of bellows units positioned
parallel to longitudinal axis C of the coupler, of which 120b and
120e are shown in FIGS. 6A and 6B. The actuator support 122 is
rigidly coupled to the stationary cold station 130 by the fixture
168. As shown in the cross sectional view in FIG. 7, the embodiment
shown has eight such bellows, 120 a-h, positioned in two groups of
four, all controlled simultaneously by the same pneumatic supply
125 and controller (not shown). The cold head extensions 107 may
have wing sections as circumferential ring segments. Two opposing
wing sections 167a and 167b, pass through correspondingly shaped
openings in actuator support 122 and permit locking in place, as
explained below. There may be two, three, four, or more wing
sections, each with a corresponding opening between flange
elements. The actuators act upon the wing sections.
[0066] A cold object vacuum container 108 surrounds the cold object
137, and is coupled to the stationary cold station 130 by a
re-entrant enclosure wall member 109. Another vacuum container 124
partially surrounds the cooling device and is also rigidly coupled
to the cold object vacuum container 108 through a ring 114. The
cooling device vacuum container 124 is flexibly attached to an end
vacuum flange 170 through a flexible wall 144 and a flange 123. The
wall member 109 is optionally re-entrant to increase the length of
the thermal path between the cold object and the warm surroundings.
The wall 144 may be flexible, as shown, to accommodate changes in
size, as the various parts change temperature, and also to
accommodate the motion of the cooling device as it is inserted and
removed.
[0067] An engagement sequence for the single stage device is as
follows. First the cryocooler is inserted into the coupler. Then
the cryocooler is rotated to the position where the wings 107 are
opposite bellows 120b, 120e, etc. Then the flange 114 is sealed and
the vacuum space of the cryocooler is pumped out. Next, the
actuator bellows 120a-120h are engaged by expansion of a gas that
fills within their chambers, supplied through supply lines 121e,
121b, which are in turn supplied by a central supply line 125 from
an external source of gas, for instance, helium. When pressure is
applied to fill the pneumatic chamber of each bellows of the
actuator, the chamber expands, forcing the cold head extension
wings 107 away from the stationary actuator support 122. The
cryocooler with the cold head extension 107 moves toward the cold
station 130, closing the gap 136. The actuator fully extends, and
presses the cold head extension firmly into the cold station 130
thereby establishing the thermal path from the cold head 106 to the
cooled object 137, through the indium gasket 169 bonded to the cold
head extension.
[0068] No unbalanced external force is applied to the cooled
object, because the force necessary to establish the thermal path
is established by expanding the bellows 120b, 120e, etc., with
balanced forces upon the actuator support 122 and the cold station
130. An indium gasket may be adhered to the face of the cold head
extension 107 facing the cold station 130. The cooled object 137 is
thermally connected with the cold station 130 through the cold
anchor 162 for instance by bolts 135. No unbalanced force is
applied from the coupler to the cooled object, to the cooling
device body, and to the vacuum walls of the cooling device or the
cooled object. The coupling forces in the thermal coupling are
self-contained in the circuit consisting of extension of the cold
head of the cooling device, actuator, and actuator support
connected with the cold station.
[0069] FIG. 6B shows the coupler in a configuration with the gap
136 closed, and the cold head extension pressing firmly against the
cooling device surface of the cold station through the indium
gasket 169.
[0070] FIG. 7, which is an end view of the coupler along the lines
7-7 of FIG. 6A, with the cooling device rotated away from the
position shown in FIGS. 6A and 6B, and retracted so that the wings
167a and 167b are at the same level as the actuator ends, helps to
illustrate how the cooling device is inserted and removed from the
coupler. As described above, in general, partially circumferential
flanges on each of the cooling device and portions of the coupler
are shaped and sized to allow passing the cooling device through an
opening in the coupler when the cooling device is in a first
rotational orientation relative to the coupler, and to prevent such
insertion (and removal) and passing when the cooling device is not
in the first rotational orientation.
[0071] For instance, the cold head extension 107 may have a pair of
wings 167a and 167b that are oppositely positioned across the
central axis C of the cooling device, which wings are sized to fit
within correspondingly shaped openings in the circumferential
extent of the actuator support 122. To insert the cooling device,
the wings 167a and 167b are lined up with the respective openings,
and the cooling device is inserted along the axis C. After the cold
head extension has passed through the opening 131, it is rotated
90.degree. around the C axis, so that the wings become aligned with
the bellows 120 a-h, and is thereby locked against removal. It can
translate a small distance, within the space between the bellows
120 a-h and the, of the cold station 130.
[0072] Rather than wings and mating openings, other mechanical
schemes for relatively quick disengagement and re-engagement can be
used. Such examples include, but are not limited to: bayonet-type
pin and slot; various sorts of a clutch, e.g. roughly analogous to
an automotive disk brake, expandable cylindrical sections that
engage a surrounding wall, radially extendable arms, or other
members.
[0073] FIGS. 6A, 6B and 7 do not show any actuator for disengaging
the cold head 106 from the cold object 107, analogous to the
retraction actuator handle and rod 34 of the two stage coupler
shown in FIG. 1A. Any suitable means can be used to retract the
cooling device, such as by gripping and pulling on the head 102. In
this case the tensile forces are transferred to the cooling device
body. The tensile forces have less potential for damage than
compressive forces, which pose the risk of possible buckling. But,
in any case, no forces are transferred to the cooled object. Also
an retracting actuator rod (not shown) can be used, pulling the
cold head extension 107 to the left (as shown). In this case
practically no forces are transferred to the cooling device
either.
[0074] The cooled object has its own separate vacuum space bordered
by cold object vacuum container 108, shared reentrant wall 109, and
the cold thermal station 130. The cooling device has its own vacuum
space bordered by the cold station 130 also, shared re-entrant wall
109, cooling device vacuum container 124, flange 123, flexible
bellows wall 144, and end flange 170. Breaking the vacuum of the
cooling device doesn't have any influence on the cooled object
vacuum. The cooling device can be replaced without breaking the
cooled object vacuum.
[0075] As with the two-stage embodiment discussed above, the
fixture and actuator arrangement need not be as shown. What is
required is that the fixture and actuator provide engagement of the
thermal conduction path between the object to be cooled and the
cooling object without any unbalanced forces applied externally to
the object to be cooled, to the cooling device body, and to the
vacuum walls of the cooling device or the cooled object.
[0076] For a one stage embodiment of the type shown in FIG. 6A,
another beneficial effect is that the cooling device itself need
not be compressed or experience any external, unbalanced force, in
the same manner as the cooled object remains free of such forces in
both embodiments. As shown, the cold stage wing extensions 107 are
bolted to the cold stage 106, in the same manner as the cold anchor
162 is bolted (or otherwise attached) to the cold station 130.
Thus, upon engagement and further pressure to establish the thermal
path, the cooling device is not compressed. The only force upon it
is at the flange that is bolted or secured in some other way to the
wings 107. But the force within this joint is contained within the
elements of the joint, and does not vary as the engagement pressure
increases.
[0077] A further benefit of such a one stage device, as shown, is
that no forces arise in the walls of either of the vacuum
enclosures, 108 of the cooled object or 124 of the cooling
device.
[0078] In a two stage embodiment, the actuators are shown acting
directly on the first, warmer stage of the cooling device. However,
this need not be the case. The actuators could alternatively have
been placed acting directly upon the colder second stage of the
cooling device, for instance if fitted with wings analogous to
wings 107 in the one stage embodiment (in which case, the cooling
device body could be under tension between two stages) or, upon
both stages. Such a design, with the actuator acting directly at
both stages, permits that no compressive forces transfer to the
cooling device body.
[0079] While particular embodiments have been shown and described,
it will be understood by those skilled in the art that various
changes and modifications may be made without departing from the
disclosure in its broader aspects. It is intended that all matter
contained in the above description and shown in the accompanying
drawings shall be interpreted as illustrative and not in a limiting
sense.
[0080] The cooled object could be a superconducting magnet,
cryogenic magnet (made of non-superconducting wires, with a very
low electrical resistance at cryogenic temperatures), infrared
detectors (for instance for a night vision and temperature
measurements), space instruments (bolometers) for measurements of
earth temperature, different electronic devices, cryo-medical and
cryo-surgical instrumentation and equipment, etc. Important
features, common with all of these devices, are: separate vacuum
thermal insulation for both source of cooling and cooled object;
and the ability to disconnect the source of cooling and replace it
without breaking the insulating vacuum of the cooled object (and
not to warm it up).
SUMMARY
[0081] An important apparatus embodiment of an invention hereof is
a coupler for thermally coupling a cooling device having at least
one cooling stage, to an object to be cooled. The coupler
comprises: a cold station configured to couple with a cold stage of
a cooling device and configured to connect with an object to be
cooled. Mechanically rigidly connected to the cold station, is an
actuator support, between which and the cold station, the cold
stage of the cooling device fits, movably. A coupling actuator is
arranged to apply substantially equal and opposite forces to the
cold stage and the actuator support, thereby forcing the cold stage
from an uncoupled configuration into a coupled configuration, with
the cold stage contacting the cold station, without any force being
applied to the object to be cooled. The apparatus also comprises a
cooling device vacuum enclosure, shaped and sized to house a
cooling device vacuum around the cooling device, comprising the
cold station; and a cooled object vacuum enclosure, shaped and
sized to house an object to be cooled, also comprising the cold
station, arranged to house a cooled object vacuum that is
hydraulically independent from the cooling device vacuum.
[0082] In a related important embodiment the cold stage contacts
the cold station without any force being applied to the cooling
device. It may also be that the cold stage contacts the cold
station without any force being applied to the cooling device
vacuum enclosure. A related important embodiment has the cold stage
contact the cold station without any force being applied to the
cooled object vacuum enclosure. It may also be that the cold stage
contacts the cold station without any force being applied to any
of: the cooling device the cooling device vacuum enclosure, or the
cooled object vacuum enclosure.
[0083] With all of the related inventions hereof, it is
advantageous for the cold station to be configured to connect
fixedly with an object to be cooled.
[0084] For any invention disclosed herein, it is useful that an
indium gasket be thermally coupled to the cold stage.
[0085] With a very important embodiment, the actuator comprises a
pneumatic actuator. The actuator may comprise a plurality of
pneumatic actuators, arranged to operate in parallel, which
actuators may be bellows. The pneumatic actuator is beneficially a
helium powered actuator.
[0086] In general, it is useful that the actuator support comprise
a surface arranged substantially facing and opposite the cold
station. In such a case, the actuator comprises a linearly
extendible member, coupled to the actuator support surface and
pushing the cold stage of the cooling device, toward the cold
station, upon energization.
[0087] An additional important related embodiment, further
comprises a releasable couple that releasably couples the cold
stage with the coupler. The cold stage may, in such a case,
comprise a device circumferential flange. The releasable couple
comprises a coupler circumferential flange, connected to the cold
station, with the device flange and the coupler flange being shaped
and arranged so that: with the cooling device in a first rotational
position, translation of the cold stage relative to the coupler is
limited to a range of inserted positions; and with the cooling
device in a second rotational position, translation of the cold
stage relative to the coupler is free to move beyond the range of
inserted positions. The releasable couple may alternately comprise
a clutch.
[0088] For still another related embodiment of an apparatus
invention hereof further the cooling device comprises a
cryocooler.
[0089] With yet another important embodiment the object to be
cooled comprises a magnet.
[0090] An embodiment of an apparatus invention hereof further
comprises: an object to be cooled; and an apparatus coupled
functionally to the object to be cooled. With such an embodiment,
the object to be cooled may advantageously comprise a magnet and,
further, the apparatus coupled functionally to the object to be
cooled may comprise a magnetic resonance imaging apparatus.
[0091] A related embodiment of an apparatus invention hereof
further comprises a cooling device, which may be a cryocooler.
[0092] With each of the apparatus embodiments of inventions hereof,
there may be a retraction actuator, coupled to the cold stage,
which retraction actuator is a different actuator from the coupling
actuator, the retraction being actuator arranged to move the cold
stage from the coupled position to an uncoupled position.
[0093] A related important embodiment of an apparatus invention
hereof is a coupler for thermally coupling, a cooling device to an
object to be cooled, where the cooling device is a type having at
least a first and a second, colder, cooling stages, which stages
are rigidly coupled to each other. The coupler comprises: an
intermediate temperature station, configured to couple releasably
with the first stage of the cooling device; a cold station,
configured to fixedly connect to the object to be cooled and also
to couple releasably with the second, colder stage of the cooling
device; and a fixture that rigidly connects the cold station to an
actuator support. This embodiment also includes an actuator that
couples the actuator support to the intermediate temperature
station, the actuator and fixture being configured such that
energization of the actuator causes the intermediate temperature
station to move away from the actuator support, and also brings
into contact: i. the intermediate temperature station with the
first stage, of the cooling device; and the cooling device colder
stage with the cold station. Forces are thereby established on the
first stage and the colder stage, which forces are substantially
equal and opposite to each other, without any force being applied
to the cold object. This embodiment also comprises a cooling device
vacuum enclosure shaped and sized to house a cooling device vacuum
around the cooling device, comprising the cold station; and a
cooled object vacuum enclosure, shaped and sized to house an object
to be cooled, the cooled object vacuum enclosure being
hydraulically independent of the cooling device vacuum enclosure,
such that a vacuum within the cooling device vacuum enclosure can
be broken without breaking a vacuum within the cooled object vacuum
enclosure.
[0094] More specifically, the cooling device may comprise a body
with the first stage at a first location between a first and a
second end of the body, and the colder stage being located at the
second end of the body. The fixture then comprises an enclosure
into which the cooling device fits, the enclosure comprising a
rigid wall that is fixed to the actuator support and extends
therefrom, toward and beyond the intermediate temperature station
and further toward the cold station, extending beyond the colder
stage of the cooling device when the cooling device is inserted
within the fixture. The associated actuator comprises a linearly
extendable actuator which, upon energization: forces a movable end
of the actuator in the direction toward the cold station and away
from the actuator support until the movable end of the actuator
meets the intermediate temperature station; and further forces the
intermediate temperature station to move in the direction of the
colder stage of the cooling device to cause contact between the
intermediate temperature station and the first stage of the cooling
device, also forcing the first stage, and the entire cooling
device, including the second colder stage, in the direction of the
colder stage of the cooling device, such that pressure increases at
an interface joining the colder stage and the cold station as well
as at an interface joining the intermediate temperature station and
the first stage of the cooling device, without any force being
applied to the object to be cooled.
[0095] Regarding an important variation of an apparatus invention
hereof, the actuator has an uncoupled position, and the coupler is
configured such that with the actuator in the uncoupled position,
the intermediate temperature station and the first stage are
mechanically and thermally uncoupled and the cold station and the
colder stage are mechanically and thermally uncoupled. With such a
device the actuator has a range of motion, and the coupler is
configured such that with the actuator in a coupled position, the
intermediate temperature station and the first stage of the cooling
device are mechanically and thermally coupled. The coupler of such
an apparatus may further be configured such that with the actuator
in a coupled position, the cold station and the colder stage of the
cooling device are mechanically and thermally coupled. According to
one variation the coupler can be configured such that with the
actuator in the coupled position, as the actuator is powered to
expand, pressure and thermal coupling between the cold station and
the colder stage of the cooling device increases, without any force
being applied to the object to be cooled.
[0096] As with the embodiments described above for a single stage
cooling device, with the two or more stages, the actuator may
comprising a pneumatic actuator, either single or a plurality,
which plurality may be arranged in parallel. The actuators may be
powered by helium gas supply.
[0097] An advantageous embodiment has the actuator support member
comprising a surface arranged substantially facing the cold
station, the actuator comprising a linearly extendible member,
coupled to the actuator support surface and the cold stage of the
cooling device, to push the cooling device away from the actuator
support when the actuator is energized, toward the colder end of
the cooling device.
[0098] Such a coupler may further comprise a couple that releasably
couples the cooling device with the coupler. In such a case, the
cooling device may comprise a device flange, and the intermediate
temperature station may comprise a flange element. The device
flange and the intermediate temperature station flange element are
shaped and arranged so that: with the cooling device in a first
rotational position, translation of the first stage relative to the
coupler is limited to a range of inserted positions; and with the
cooling device in a second rotational position, the first stage is
free to translate relative to the coupler beyond the range of
inserted positions. A convenient configuration to achieve this has
the intermediate temperature station flange element comprising
openings, the actuator support comprising openings, and the cooling
device first stage comprising wings, which fit within the openings
of the intermediate temperature station flange element and of the
actuator support.
[0099] As with the one stage cooler embodiment, for a two or more
stage embodiment, the cooling device may comprise a cryocooler and
the object to be cooled may comprise a magnet. The apparatus
coupled functionally to the object to be cooled may comprise a
magnetic resonance imaging apparatus or a proton beam radiation
treatment apparatus. The cooling device can further be part of the
coupler. Finally, there can be a retraction actuator, coupled to
the first stage, which retraction actuator is a different actuator
from the coupling actuator, the retraction actuator being arranged
to move the first stage from a coupled position to an uncoupled
position.
[0100] The engagement actuator can be applied to directly push the
intermediate station toward the intermediate stage of the cooling
device as shown, or it can be applied to directly push the cold
stage of the cooling device toward and into contact with the cold
station, or the actuator can be connected to directly contact both
the intermediate and cold stages of the cooling device. Or, there
can be two such actuators, one for each stage.
[0101] Important aspects of inventions disclosed herein are also
methods, of which an important embodiment is a method to thermally
couple a cooling device having at least one cooling stage to an
object to be cooled. The method comprises the steps of: providing a
thermal coupler comprising: a cold station connected with the
object to be cooled and configured to couple, with a cold stage of
the cooling device; mechanically rigidly connected to the cold
station, an actuator support, between which and the cold station,
the cold stage fits, movably. Connected to the cold stage, at least
one wing extension is configured to fit through at least one
corresponding opening in the actuator support; an engagement
actuator is arranged to apply substantially equal and opposite
forces to the at least one wing extension of the cold stage and the
actuator support, upon energization, thereby forcing the cold stage
from an uncoupled position, toward and into a coupled position,
contacting the cold station, without any force being applied to the
object to be cooled. Also part of the coupler is a cooling device
vacuum enclosure shaped and sized to house a cooling device vacuum,
around the cooling device, comprising the cold station; and a
cooled object vacuum enclosure, shaped and sized to house an object
to be cooled, arranged to house a cooled object vacuum that is
hydraulically independent from the cooling device vacuum. The
method also includes the steps of introducing the cooling device
into the cooling device vacuum enclosure, such that the at least
one wing extension passes through the corresponding opening in the
actuator support, and positioning the cold stage of the cooling
device in an uncoupled position between the actuator support and
the cold station; and rotating the cooling device so that the at
least one wing extension is opposite the actuator. The final step
of the general description of this method is energizing the
actuator, so that it engages the wing extension, thereby forcing
the cold stage from an uncoupled position, toward a coupled
position, contacting the cold station, without any force being
applied to the object to be cooled.
[0102] As with the apparatus embodiments discussed above, the
method embodiments of the inventions hereof can be accomplished
with many of the apparatus discussed above. For instance, the
actuator may comprise a pneumatic actuator, and the step of
energizing the actuator may comprise increasing the pressure of a
gas provided to the actuator. The gas may be helium. The actuator
may be sole, or a plurality, which plurality may operate in
parallel.
[0103] The method may further comprise the step of establishing a
vacuum within the cooling device vacuum enclosure, followed by
activating the cooling device. Activating the cooling device may
take place either before or after energizing the actuator.
[0104] A final step in the method of coupling may be decoupling,
accomplished by providing a retraction actuator, coupled to the
cold stage, which retraction actuator is a different actuator from
the coupling actuator, with the method to couple further comprising
the step of energizing the retraction actuator to move the cold
stage from the coupled position to an uncoupled position.
[0105] A very important embodiment of an invention hereof is a
method to thermally couple a cooling device having a first and a
second, colder, cooling stages, to an object to be cooled. The
cooling device stages are rigidly connected to each other. The
method comprises the steps of: providing a thermal coupler
generally of a type described above, for instance comprising: an
intermediate temperature station, configured to couple releasably
with the first stage of the cooling device; a cold station,
configured to fixedly connect to the object to be cooled and also
to couple releasably with the second, colder stage of the cooling
device; and a fixture that rigidly connects the cold station to an
actuator support. Connected to the first stage, at least one wing
extension is configured to fit through at least one corresponding
opening in the intermediate temperature station. An actuator
couples the actuator support to the intermediate temperature
station. The actuator and fixture are configured such that
energization of the actuator moves the intermediate temperature
station, away from the actuator support and also brings into
contact: the intermediate temperature station with the first stage
of the cooling device; and the cooling device colder stage with the
cold station. Forces are thereby established on the first stage and
the colder stage, which forces are substantially equal and opposite
to each other, without any force being applied to the object to be
cooled. The device that is provided also comprises: a cooling
device vacuum enclosure shaped and sized to house a cooling device
vacuum that surrounds the cooling device, comprising the cold
station; and a cooled object vacuum enclosure, shaped and sized to
house an object to be cooled, the cooled object vacuum enclosure
being hydraulically independent of the cooling device vacuum
enclosure, such that a vacuum within the cooling device vacuum
enclosure can be broken without breaking a vacuum within the cooled
object vacuum enclosure. The method of coupling also includes the
steps of: introducing the cooling device into the cooling device
vacuum enclosure such that the at least one wing extension passes
through the corresponding opening in the actuator support;
positioning the first stage of the cooling device in an uncoupled
position by rotating the cooling device so that the at least one
wing extension is opposite the intermediate temperature station;
and energizing the actuator, so that contact arises between: the
intermediate temperature station with the first stage of the
cooling device; and the cooling device colder stage with the cold
station.
[0106] For an important embodiment, the actuator comprises a
pneumatic actuator, and the step of energizing the actuator
comprises increasing the pressure of a gas provided to the
actuator.
[0107] The method to couple the two stage embodiment may further
comprise the step of establishing a vacuum within the cooling
device vacuum enclosure followed by activating the cooling device.
Activating the cooling device may take place before or after
energizing the actuator.
[0108] Helium gas may be introduced into the cooling device vacuum
enclosure.
[0109] As with a one stage configuration, there may also be
provided a retraction actuator, coupled to the cooling device,
which retraction actuator is a different actuator from the coupling
actuator, and the method to couple may further comprise the step of
energizing the retraction actuator to move the cold stage from the
coupled position to an uncoupled position.
[0110] Many techniques and aspects of the inventions have been
described herein. The person skilled in the art will understand
that many of these techniques can be used with other disclosed
techniques, even if they have not been specifically described in
use together. For instance, for a two or more stage cooling device,
the coupling actuator can be coupled directly to the intermediate
temperature station or to the cold stage, or both. The retraction
actuator can similarly be coupled directly to either or both
stages. The specific arrangement of an actuator support and a
fixture that rigidly connects the support to the cold station may
take a different geometric path or shape, as long as it permits
applying a balancing force to the cold station that is equal and
opposite to the force that is applied at the cold station by the
cold stage, so that no unbalanced force remains to affect the cold
object. The type of fixture shown may be used with a wing and
opening flange type quick-connect mechanism, or a clutch, or any
other releasable coupling mechanism. The actuator need not be
linearly expanding, but can be rotary, or some other
configuration.
[0111] This disclosure describes and discloses more than one
invention. The inventions are set forth in the claims of this and
related documents, not only as filed, but also as developed during
prosecution of any patent application based on this disclosure. The
inventors intend to claim all of the various inventions to the
limits permitted by the prior art, as it is subsequently determined
to be. No feature described herein is essential to each invention
disclosed herein. Thus, the inventors intend that no features
described herein, but not claimed in any particular claim of any
patent based on this disclosure, should be incorporated into any
such claim.
[0112] Some assemblies of hardware, or groups of steps, are
referred to herein as an invention. However, this is not an
admission that any such assemblies or groups are necessarily
patentably distinct inventions, particularly as contemplated by
laws and regulations regarding the number of inventions that will
be examined in one patent application, or unity of invention. It is
intended to be a short way of saying an embodiment of an
invention.
[0113] An abstract is submitted herewith. It is emphasized that
this abstract is being provided to comply with the rule requiring
an abstract that will allow examiners and other searchers to
quickly ascertain the subject matter of the technical disclosure.
It is submitted with the understanding that it will not be used to
interpret or limit the scope or meaning of the claims, as promised
by the Patent Office's rule.
[0114] The foregoing discussion should be understood as
illustrative and should not be considered to be limiting in any
sense. While the inventions have been particularly shown and
described with references to preferred embodiments thereof, it will
be understood by those skilled in the art that various changes in
form and details may be made therein without departing from the
spirit and scope of the inventions as defined by the claims.
[0115] The corresponding structures, materials, acts and
equivalents of all means or step plus function elements in the
claims below are intended to include any structure, material, or
acts for performing the functions in combination with other claimed
elements as specifically claimed.
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