Apparatus and method for providing a thermally conductive bond

Abstract

An apparatus for cooling an object (601) moving in a cryostat includes a heat transfer part (602) forming a contact surface with the object (601) and means for fastening the heat transfer part (602) to a cooling structure (604) so ​​as to leave the contact surface free. The apparatus includes a spring part (605) separate from the heat transfer part (602) and arranged to apply a spring force (606) to the heat transfer part (602) that urges the contact surface toward contact with the object (601).

Description

[Technical Field]

[0001] The present invention relates generally to cryostats in which an object being cooled is introduced into the cryostat in such a way that heat is conducted from the object being cooled to the structure of the cryostat. Specifically, the present invention relates to a method for providing an efficient thermally conductive bond. [Background technology]

[0002] Cryostats are used to cool objects to very low temperatures. Generally, the object being cooled is called the sample, and the area to be cooled to the lowest temperature is called the target area. There are two different options for getting the sample to the target area. In the most traditional way, the entire cryostat is heated and opened, the sample is manually clamped into the target area, the cryostat is closed, and the entire cryostat with the sample is cooled again. A sample changer can be installed in the cryostat to allow for rapid sample exchange.

[0003] Figure 1 is a schematic diagram of a cryostat equipped with a sample changer. This cryostat uses two-stage mechanical pre-cooling, with a dilution refrigerator at the innermost stage. The outermost vacuum chamber 101 of the cryostat is shown in dashed lines. The top 103 of the mechanical pre-cooler is covered by a room-temperature flange 102 to which it is clamped. The first stage 104 of the mechanical pre-cooler is clamped to the first cooling flange 105, and the second stage 106 is clamped to the second cooling flange 107. The dilution refrigerator's still 109 is located on the third cooling flange 108. The dilution refrigerator's mixing chamber 110 is clamped to the fourth cooling flange 111. For clarity, a thermally adjustable connection between the flanges may be included, not shown. The target area 112 where the sample is clamped is part of the fourth cooling flange 111 or is otherwise in communication with the mixing chamber 110 to ensure as good thermal conductivity as possible. During operation, the temperature of the first cooling flange 105 may be a few tens of Kelvin, the temperature of the second cooling flange 107 may be about 4 K, the temperature of the third cooling flange 108 may be about 1 K, and the temperature of the fourth cooling flange 111 may be only a few milliKelvin.

[0004] The cryostat of FIG. 1 includes a top-loader sample changer; alternatively, solutions of the bottom-loader type or clamped to the side of the vacuum chamber are known from the prior art. The sample holder includes a vacuum tube 113 hermetically clamped to a gate valve 114 of the vacuum chamber. The sample, not separately shown in FIG. 1, is clamped to a sample holder 115 that is first drawn into the vacuum tube 113. When the vacuum tube 113 is clamped to the gate valve 114 and evacuated, the sample holder 115 can be pushed into position at the target area 112 using one or more probes 116. For this purpose, all flanges and other structures located along its path must include matching holes, forming a so-called clear shot.

[0005] If the sample and sample holder 115 are at room temperature when they reach the target area 112, the heat they contain must be transferred from the innermost part to the outer part throughout the cryostat. This is possible, but slow, because, for understandable reasons, all heat transfer between the outside air and the innermost part of the cryostat is minimized during operation. Also, the innermost cooling device of the cryostat can reach the lowest temperature, but has the weakest cooling power. It is often more advantageous to pre-cool the sample and sample holder on their way to the target area. Mechanical contact or a thermally conductive gas may be used to form a thermally conductive bond between the sample holder and a suitable cooling unit.

[0006] 2 and 3 show the pre-cooling principle known from Patent Document 1. Here, the flange hole 201 and the sample holder 115 are not circular, but rather have a shape such that in one rotational position, the outermost part of the sample holder 115 abuts the flange adjacent to the hole 201. These parts are provided with a threaded hole 301. In addition to or instead of the focusing probe 116, the sample changer may include a threadable rod 202, so that the sample holder 115 can be temporarily fastened to the flange by a screw located at the outermost end of the threadable rod (or by means of a separate bolt that rotates relative to the threadable rod), as shown in FIG. 2. When sufficient pre-cooling has been provided, the screw or bolt is removed, and the sample changer is rotated to the appropriate position so that it can be moved through the flange hole 201, as shown in FIG. 3. The screw or bolt may also be used to secure the sample holder 115 to the target area.

[0007] The solutions shown in Figures 2 and 3 have several drawbacks. First, the design of the sample holder is limited, and the drilling of the flange holes becomes more complicated. Second, friction caused by the tightening of the screws or bolts must be taken into account. Metals and other solids have a very low specific heat capacity when cold, so even a small amount of heat generated by friction may be enough to warm the object they interact with by a few degrees. Furthermore, the structure is highly dependent on the physical dimensions of the mechanical object, which shrink as the temperature decreases. Since the object's dimensions change upon cooling, the requirement for mechanical compatibility may cause problems with the operability of the mechanism.

[0008] The use of thermally conductive springs is known in the art and is illustrated in Figures 4 and 5. A sample 401 is clamped into a sample holder 115, which here is generally disc-shaped and made from a material with good thermal conductivity. A plurality of springs 402, a resilient and thermally conductive material, are clamped around holes in the flange 105. As shown in Figure 5, when the sample holder 115 is pressed between the springs, the springs bend outward and are pressed against the edges of the sample holder 115 by their spring force.

[0009] A drawback of the solutions shown in Figures 4 and 5, at least for the present invention, is the lack of a material that is both sufficiently elastic and has sufficiently high thermal conductivity. When two solid bodies come into contact with each other, thermal conductivity is highly dependent on the amount of force pressing the two solid bodies toward each other, so good elasticity is necessary. Copper is a good example of a material that has good thermal conductivity but does not bend. When used as a "spring," a copper piece bends to its outward position upon initial use and does not return to its original position, causing all subsequent precooling attempts to fail due to poor contact. On the other hand, a beryllium copper alloy allows the spring to maintain its properties well, but its very low thermal conductivity necessitates coating the spring with gold or silver. However, this coating is necessarily thin so that the composite cross-section with good thermal conductivity between the sample holder 115 and the flange 105 is relatively small. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] European Patent No. 2409096B1 Summary of the Invention [Problem to be solved by the invention]

[0011] It is an object of the present invention to provide an apparatus and method for efficiently cooling objects placed in a cryostat. Another object of the present invention is to provide an apparatus and method that is durable without loss of efficiency even after several uses. An additional object of the present invention is that it is applicable to cooling multiple objects of different sizes or shapes. A further object of the present invention is that the required apparatus parts can be manufactured from commonly available materials using conventional machining methods.

[0012] The objectives of the present invention are achieved by using a heat transfer portion in the structure and a separate spring portion, the resilience of which biases the heat transfer portion into good contact with the object being cooled. [Means for solving the problem]

[0013] An apparatus for providing a thermally conductive coupling for cooling a moving object in a cryostat according to the present invention comprises: a heat transfer portion that forms a contact surface with the object; means for fastening the heat transfer portion to the cooling structure so that the contact surface is free; The spring portion is separate from the heat transfer portion and is arranged to apply a spring force to the heat transfer portion that presses the contact surface in a direction that brings the object into contact with the heat transfer portion.

[0014] In one embodiment, the heat transfer section comprises a plurality of heat transfer elements arranged in a ring, the contact surface being formed by the surfaces of the heat transfer elements facing inwards of the ring, which has the advantage that a large proportion of the outer surface of the object being moved inside the cryostat is available for heat transfer needs.

[0015] In one embodiment, the spring portion includes one or more spring elements arranged outside the ring of heat transfer elements and pushing the heat transfer elements toward the center of the ring, which has the advantage of symmetrically applying the necessary pushing force for efficient heat transfer to objects moving within the cryostat.

[0016] In one embodiment, the device includes means for supporting the spring portion to the cooling structure, which has the advantage of making it easier to control the magnitude or direction of the applied spring force.

[0017] In one embodiment, the heat transfer portion includes a clamping ring having an inner edge and a plurality of heat transfer pieces, each having one end clamped to the inner edge of the clamping ring and another free end oriented substantially perpendicular to a plane defined by the clamping ring, which has the advantage of facilitating the manufacture of the heat transfer portion to a precise desired size or shape.

[0018] In one embodiment, the spring portion includes a support ring fastened to the upper portion of the clamping ring and having an inner surface, and a plurality of spring pieces supported by the inner surface of the support ring and arranged to apply the spring force to the heat transfer piece, which has the advantage of being able to apply a desired spring force to the heat transfer piece.

[0019] In one embodiment, the spring pieces form a continuous band of spring pieces that extend around the inner surface of the support ring and are supported in one or more grooves in the inner surface of the support ring, which provides an advantageous manufacturing technique for producing the spring portion.

[0020] In one embodiment, the device further includes an upper clamping ring clamped to an upper portion of the support ring and arranged to support a free end of each heat transfer piece at a position farther from the center line of the ring formed by the heat transfer pieces than the center of the heat transfer pieces, which has the advantage that the position of the heat transfer pieces is particularly good with respect to movement of an object during movement within the cryostat.

[0021] In one embodiment, the heat transfer part is made of copper or silver, which has the advantage that the heat transfer part has high thermal conductivity.

[0022] In one embodiment, the heat transfer part made of copper or silver is coated with gold, which has the advantage that the relevant surface of the heat transfer part does not oxidize and can maintain good thermal conductivity over time.

[0023] In one embodiment, the spring portion is manufactured from a beryllium copper alloy, which has the advantage that the spring portion has elastic properties suitable for use in extremely low temperature environments such as cryostats.

[0024] An arrangement for cooling an object in motion in a cryostat according to the invention comprises a cooling structure and a device according to any of the above descriptions arranged in the cooling structure.

[0025] In one embodiment, the arrangement includes a first cooling structure and a first device as described above disposed on the first cooling structure. In this case, the arrangement may include a second cooling structure and a second device as described above disposed on the second cooling structure. The first cooling structure may include an opening concentric with the first and second devices. In the first device, the contact surfaces of the devices may form a ring having a first diameter. In the second device, the contact surfaces of the devices may form a ring having a second diameter smaller than the first diameter. The diameter of the opening may be larger than the first and second diameters. This has the advantage that an object moving within a cryostat may include two parts of different diameters, arranged so that both parts are compatible for heat transfer through a particular device.

[0026] In one embodiment, the second cooling structure defines a target area in the cryostat where the object being cooled is clamped, thereby having the advantage of cooling the object as much as possible by heat transfer.

[0027] In one embodiment, the arrangement includes a sample holder forming at least part of the object in motion within the cryostat, the sample holder comprising a first section having a diameter corresponding to the first diameter and a second section having a diameter corresponding to the second diameter, the second section being arranged in a part of the sample holder that is positioned relative to the first section in the same direction as the second cooling structure is positioned relative to the first cooling structure, which has the advantage that the second section is not damaged in the previous cooling step and is therefore as little damaged as possible when used in the cooling step. [Brief explanation of the drawings]

[0028] [Figure 1] A cryostat is shown. [Figure 2] 1 shows a known pre-cooling solution. [Figure 3] 3 shows a subsequent stage of use of the solution according to FIG. 2. [Figure 4] 1 shows a known pre-cooling solution. [Figure 5] 5 shows a later stage of use of the solution according to FIG. [Figure 6] The principle of efficient pre-cooling is shown. [Figure 7] 1 illustrates an embodiment for performing pre-cooling. [Figure 8] 8 shows one element of the solution of FIG. 7. [Figure 9] 1 illustrates an embodiment for performing pre-cooling. [Figure 10] 1 illustrates an embodiment for performing pre-cooling. [Figure 11] 1 illustrates an embodiment for performing pre-cooling. [Figure 12] 12 shows further details of the embodiment of FIG. 11. DETAILED DESCRIPTION OF THE INVENTION

[0029] 6 illustrates the principle of an apparatus for providing a thermally conductive coupling for the purpose of cooling a moving object 601 in a cryostat. The moving object 601 is referred to as a sample holder in FIG. 6, but it may also be any other moving object. The actual purpose may be to move and cool another item, such as a sample clamped in the sample holder. However, in practice, such an indirectly moving item (e.g., a sample) and the item that moves it (e.g., a sample holder) may generally be considered as one moving object 601 in a cryostat.

[0030] In the principle shown in Fig. 6, the device includes a heat transfer part 602 that forms a contact surface with an object 601. Therefore, the objective is to bring the moving object 601 and the heat transfer part 602 into physical contact with each other so that heat can be transferred between them by conduction from one solid object to the other. The thermally conductive bond based on physical contact between the objects is indicated by cross-hatching in Fig. 6. The heat transfer part 602 may consist of one or more parts.

[0031] In the principle shown in Fig. 6, the device includes a means 603 for fastening a heat transfer part 602 to a cooling structure 604. This fastening is specifically provided so that a contact surface of the heat transfer part 602 is free to come into contact with a moving object 601. The above-mentioned condition is natural in the sense that without a free contact surface, it is difficult or impossible to bring the moving object 601 into thermally conductive contact with the heat transfer part 602. There is a thermally conductive bond between the heat transfer part 602 and the cooling structure 604, which is indicated by cross-hatching in Fig. 6.

[0032] 6, the device includes a spring portion 605 that is separate from the heat transfer portion 602 and is arranged to apply a spring force 606 to the heat transfer portion 602. The spring force 606 pushes the contact surface of the heat transfer portion 602 in a direction that brings the moving object 601 into contact with the contact surface.

[0033] The separation of the heat transfer portion 602 and the spring portion 605 means that, in contrast to the prior art, it is not intended that the same structural element provides both heat conduction between the object 601 and the cooling structure 604 and the force maintaining the heat-conducting contact. The separation does not mean that the spring portion 605 and the heat transfer portion 602 must be located completely separate from each other in different parts of the structure. It means that the spring portion 605 may be one part (or multiple parts), and the heat transfer portion 602 may be another part (or multiple other parts). The part forming the spring portion 605 may be made of a different material from the other parts forming the heat transfer portion. This is reasonable, since these parts are required to have very different properties: the most important property of the heat transfer portion 602 is the most efficient possible heat conduction between the moving object 601 and the cooling structure 604, while the most important property of the spring portion 605 is to provide a good spring force 606.

[0034] The spring portion 605 may be supported by the cooling structure 604, as indicated by reference numeral 607 in Figure 6. However, this is not required. Examples of supported and unsupported embodiments are described in more detail below.

[0035] FIG. 7 illustrates an apparatus for providing a thermally conductive coupling for cooling a moving object within a cryostat, according to one embodiment. The moving object is not shown in FIG. 7 but may be assumed to be, for example, a disk of the same type as that described in the prior art description and in FIGS. 4 and 5 . The cooling structure is one flange 105 of the cryostat. It is therefore assumed here that several cooling devices, such as the cryostat's mechanical precooler or several stages of a dilution refrigerator, remain thermally conductively coupled to flange 105 (outside the area shown in FIG. 7 ). A circular opening is provided in flange 105 for transporting the moving object. If the moving object is a sample holder being transported to a target area, the opening in flange 105 is part of a clear shot used for this purpose.

[0036] The heat transfer part of the device shown in Fig. 7 includes a plurality of heat transfer elements 701 arranged in a ring. In shape, the heat transfer elements 701 are similar to the thermally conductive springs used in prior art solutions. However, they differ in that in the embodiment shown in Fig. 7 they are not required to be elastic. The heat transfer elements 701 can be made, for example, from copper, so that they are relatively easy to bend, but have a natural tendency to maintain their position after being bent.

[0037] In the embodiment according to Fig. 7, there are also means for fastening the heat transfer part to the cooling structure. These means include a clamping ring 702 and screws 703 for fastening the clamping ring 702 to the flange 105. The outermost end of each heat transfer element 701 is tightly pressed between the clamping ring 702 and the flange 105. This ensures that a good thermally conductive bond is maintained between the heat transfer element 701 and the flange 105, which acts as the cooling structure.

[0038] The contact surface of the heat transfer section for an object moving within the cryostat is formed by the surface facing inward of the ring formed by the heat transfer elements 701. Comparing Figure 7 with Figures 4 and 5, it is easy to see that, for example, a disk-shaped sample holder is pressed into the center of the ring formed by the heat transfer elements 701 so that its cylindrical outer surface contacts each of the heat transfer elements 701 simultaneously.

[0039] In the embodiment shown in Figure 7, the spring portion of the device includes a spring element 704 disposed on the outside of a ring-shaped heat transfer element 701 and urging the heat transfer element 701 toward the center of the ring. The spring element 704 is shown separately in Figure 8. The spring element is annular and is made of spring steel, beryllium copper alloy, or other suitable material that maintains its elasticity even at the low temperatures of the cryostat.

[0040] The spring elements 704 are sized to press against the circular contact surface jointly formed by the heat transfer elements 701 to a diameter smaller than the opening in the flange 105 (and smaller than the diameter of the moving object being cooled) when at rest (when no moving object is contacting the heat transfer elements 701). When a moving object is pressed against the center of the ring, the spring elements urge the free ends of the heat transfer elements 701 outward, bending each heat transfer element 701 at a point where the vertical portion of the heat transfer element changes to a horizontal portion. Throughout this specification, directional terms such as vertical and horizontal are used to indicate the manner of representation used in the drawings and do not limit how the corresponding parts are oriented in the actual device.

[0041] The spring force generated by the spring element 704 resists the bending of the heat transfer element 701. This generates a force that presses the heat transfer element 701 firmly against the surface of the moving object in the cryostat, thereby ensuring efficient heat transfer between these parts. When the moving object is transferred away from the center of the ring formed by the heat transfer element 701, the spring element 704 presses the heat transfer element 701 back to its position before the moving object was introduced. Therefore, the device providing a thermally conductive coupling shown in FIG. 7 can be used the next time a moving object in the cryostat needs to be cooled by the device.

[0042] 9 shows another embodiment of an apparatus for providing a thermally conductive coupling for cooling an object moving within a cryostat. In the apparatus of FIG. 9, the heat transfer section forming the contact surface with the object consists of a plurality of heat transfer elements 901 arranged in a ring. Again, the contact surface is formed by the surfaces of the heat transfer elements 901 facing inward toward the ring. The heat transfer elements 901 are made of a material that has a high thermal conductivity at the operating temperature of the cryostat, such as copper or silver. They may also be coated with a coating that improves their heat transfer properties, such as a layer of gold.

[0043] 9, the means for fastening the heat transfer part to the cooling structure comprises slide rails 902, one of which is provided for each heat transfer element 901. Each heat transfer element 901 is mounted on the corresponding slide rail so as to be easily movable in the radial direction of the ring formed by the heat transfer elements 901. If necessary, the part of the heat transfer element 901 located within the slide rail 902 and / or the slide rail itself may be coated with a coating that combines good heat transfer properties with low friction at temperatures corresponding to the operation of the cryostat.

[0044] Based on the above principle, in the embodiment of FIG. 9, a spring portion is provided that is separate from the heat transfer portion. The spring portion is arranged to apply a spring force to the heat transfer portion, urging the contact surface of the heat transfer portion in a direction that contacts an object moving within the cryostat. In the embodiment of FIG. 9, the spring portion includes multiple spring elements 903 arranged outside the heat transfer elements 901 arranged in a ring shape. Specifically, in this embodiment, the number of spring elements 903 is equal to the number of heat transfer elements. The spring element corresponding to each heat transfer element 901 urges each heat transfer element toward the center of the ring. The spring elements 903 are compression springs made of spring steel, beryllium copper alloy, or other suitable material that maintains elasticity even at the low temperatures of the cryostat.

[0045] Unlike the embodiment of Figure 7, in the embodiment of Figure 9 there are means for supporting the spring elements to the cooling structure. These means include a clamping ring 904 and bolts 905 that clamp the clamping ring 904 to the flange 105. Most preferably, the inner surface of the clamping ring 904 is provided with recesses for the ends of each spring element 903 so that the spring elements 903 remain in place and oriented correctly.

[0046] Compared to FIG. 7 , the embodiment of FIG. 9 has the advantage that the heat transfer element 901 is not subjected to constant reciprocating bending, and therefore does not exhibit metal fatigue and fracture that may result from such bending. On the other hand, the disadvantages of the embodiment of FIG. 9 are the friction that inevitably occurs in the slide rail 902, which generates undesirable amounts of heat, and the thermal conductivity of the slide rail mechanism, which is lower than that of the pressure contact portion of FIG. 7 . If metal fatigue is not a major issue, the principles shown in FIGS. 7 and 9 can be combined, for example, as shown in FIG. 10 . In the embodiment shown in FIG. 10 , the heat transfer element 701 is similar to that in FIG. 7 , but the spring portion consists of a spring element 903 similar to that in FIG. 9 . In addition to the clamping ring 904 and bolt 905, the clamping means includes a lifting ring 1001 specifically designed to press the horizontal end of the heat transfer element 701 against the flange 105. Naturally, a single common ring combining the characteristics of the ring 904 and ring 1001 shown in FIG. 10 may also be used.

[0047] 9 uses hinges instead of slide rails 902. Thus, at the bottom of the vertical portion of each heat-transfer element 901, there is a hinge that contacts the ring and has a horizontal axis of rotation, allowing the vertical portion to rotate toward and away from the center of the ring. Hinges are more complex in structure than slide rails and require more individual parts and operations during assembly, but the use of hinges can achieve lower friction, more reliable operation, and less excess heat generation than the use of slide rails.

[0048] FIG. 11 illustrates an apparatus for providing a thermally conductive coupling for cooling an object moving within a cryostat, according to one embodiment. The embodiment of FIG. 11 is similar to the previously described embodiments in that the apparatus includes a heat transfer portion, a means for fastening the heat transfer portion to a cooling structure (e.g., flange 105 in FIG. 11 ), and a spring portion separate from the heat transfer portion. The heat transfer portion forms a contact surface with an object moving within the cryostat to cool the object. The fastening to the cooling structure is performed so that this contact surface is free. The spring portion is positioned to apply a spring force to the heat transfer portion that urges the contact surface toward the object.

[0049] As with the other embodiments described above, in FIG. 11 , the object being cooled is assumed to be at least partially cylindrical and move up and down through the opening in the flange 105. The heat transfer section includes a plurality of heat transfer elements 1101 arranged in a ring shape, which in this embodiment are also referred to as heat transfer strips. The contact surface is formed by the surface of the heat transfer strips 1101 facing inward toward the ring. The spring section includes a plurality of spring elements 1102 arranged outside the ring-shaped heat transfer strips 1101 and urging the heat transfer strips 1101 toward the center of the ring. The device also includes means for supporting the spring section to the cooling structure. These means include rings 1103, 1104, and 1105 and bolts 1106, the structure and operation of which are described in more detail below.

[0050] The heat transfer portion of the device according to the embodiment of Fig. 11 includes a clamping ring 1104. The dimensions of the inner edge of the clamping ring may be approximately the same as the dimensions of the opening in the flange 105, but may be larger or smaller. One end of the heat transfer piece 1101 is clamped to the inner edge of the clamping ring 1104. The free end of the heat transfer piece 1101 is oriented in a direction substantially perpendicular to the plane defined by the clamping ring 1104. As a result, in the position shown in Fig. 11, the free end of the heat transfer piece 1101 faces upward.

[0051] The unit formed by the heat transfer pieces 1101 and the clamping ring 1104 is advantageously manufactured from a material that conducts heat as well as possible at the relatively low temperatures associated with normal operation of a cryostat. Such materials include, for example, copper and silver. The heat transfer pieces 1101 and the clamping ring 1104 may also be gold-plated and / or have other coatings or surface treatments that improve their ability to form a thermally conductive bond with the components they contact. In particular, the contact surface formed by the surface of the heat transfer pieces 1101 facing the inside of the ring should advantageously be manufactured to be fairly hard so that it is not damaged by repeated sliding with the object being cooled.

[0052] The heat transfer strip 1101 may be manufactured from a sheet of material of an appropriate thickness by cutting a comb-like portion of a length corresponding to the circumference of the inner edge of the clamping ring 1104. The continuous edge of the comb-like portion may be fastened around the inner edge of the clamping ring 1104 using an appropriate metal joining method, such as welding or soldering.

[0053] The spring portion of the device according to the embodiment of Figure 11 includes a support ring 1103 clamped onto the top of a clamping ring 1104. The spring elements of the spring portion are a plurality of spring pieces 1102 supported on the inner surface of the support ring 1103 and arranged to apply a spring force to the heat transfer pieces 1101 urging them towards the center of the ring formed by the heat transfer pieces 1101.

[0054] The spring segments 1102 may be separate and may form a continuous band of spring segments that extend around the inner surface of the support ring 1103 and are supported in one or more grooves in the inner surface of the support ring 1103. In place of the spring segments 1102, coil springs as in the embodiment of Figures 9 and 10 or spring rings as in the embodiment of Figure 7 may be used.

[0055] The spring strips 1102, or other spring elements used instead, are advantageously fabricated from materials that remain elastic at the low temperatures typical of cryostat operation, including many spring steels and beryllium copper alloys.

[0056] The number of heat transfer pieces 1101 and spring pieces 1102 may vary. This type of solution has several advantages. First, it allows the dimensions of the heat transfer pieces 1101 and spring pieces 1102 to be optimized according to their respective functions (heat transfer / spring force generation); for example, the heat transfer pieces 1101 should not be too narrow in relation to their length, since the heat transfer cross-sectional area of ​​narrow pieces is small. Second, if the number of heat transfer pieces 1101 and spring pieces is different, their vertical edges do not coincide, at least in many points. This helps to press adjacent heat transfer pieces 1101 against the object being cooled with as constant a force as possible at each point. A third advantage is that, since the number is not critical in the first place, if an element is to be specifically manufactured for this purpose, it is possible to use more accessible parts for the application in other connections in the most advantageous cases.

[0057] 11 includes, in addition to the above components, an upper clamping ring 1105 that is clamped to the top of the support ring 1103 and is positioned to support the free end of each heat transfer piece 1101 at a position farther from the center line of the ring formed by the heat transfer pieces 1101 than the center of the heat transfer piece 1101 (R2>R1 in FIG. 11). Thus, the upper clamping ring 1105, together with the spring pieces 1102, ensures that each heat transfer piece 1101 is bent into a curved shape so that an object moving within the cryostat can easily move from either direction to the center of the ring formed by the heat transfer pieces 1101. The upper clamping ring 1105 is not necessary if the moving object has a conical profile sufficient for the opening of the ring formed by the heat transfer pieces 1101 and / or if the free end of each heat transfer piece 1101 is bent sufficiently far from the center line of the ring in some other way.

[0058] 11, the clamping bolts 1106 extend through the clamping ring 1104, the support ring 1103, and the upper clamping ring 1106. This is not required, and if the rings 1104, 1103 are countersunk, each ring may be fastened to the base structure by its own bolt or in any other suitable manner.

[0059] In general, each time a moving object in a cryostat slides over another part (e.g., a contact surface of a device used for cooling), scratches and abrasion can occur on the surfaces that come into contact with each other. This effect occurs in a substantially similar manner, regardless of the technical implementation of the device used for cooling, although the amount of scratches and abrasion can vary in different implementations. Both scratches and abrasion are undesirable, as they can weaken the thermal conduction between the object being cooled and the contact surface of the device used for cooling.

[0060] In particular, it is advantageous to have as good a thermally conductive bond as possible to cool the sample to a minimum temperature at the target area, however, if the same thermally conductive bond is also applied where the sample (typically the sample holder) is pre-cooled before reaching the target area, this can cause significant scratches and wear which should be avoided.

[0061] The aim is therefore to provide an arrangement which ensures as good a thermally conductive connection as possible to cool the moving object at the target area, whilst also pre-cooling other parts of the cryostat before it reaches the target area.

[0062] This objective is achieved by forming a different type of thermally conductive bond between the moving object within the cryostat and the cooling structure when the object reaches the target region than that used to pre-cool the moving object.

[0063] FIG. 12 shows an example of an arrangement for cooling an object in motion within a cryostat. The arrangement includes a first cooling structure (here, flange 108) and a first device 1201 fastened to the first cooling structure, shown here substantially similar to that of FIG. 11 but which may be an apparatus according to any of the embodiments described above. The arrangement includes a second cooling structure (here, flange 111) and a second device 1202 fastened to the second cooling structure. Here, the second device 1202 is shown substantially similar to that of FIG. 11 but which may be an apparatus according to any of the embodiments described above. The first cooling structure, i.e., flange 108, includes an opening 1203 concentric with the first device 1201 and the second device 1202.

[0064] 12 is that the first device 1201 and the second device 1202 are not exactly the same size. In the first device 1201, the contact surface of the device forms a ring with a first diameter. In the second device 1202, the contact surface of the device forms a ring with a second diameter, which is smaller than the first diameter. In one embodiment, the second cooling structure 111 forms a target area in which the object being cooled in the cryostat is clamped. Therefore, the diameter of the circular contact surface of the device located in the target area is smaller than the diameter of the device that pre-cools the object before it reaches the target area.

[0065] 12, the object moving within the cryostat is a sample holder 1204. Specifically, in this example, the sample holder 1204 forms only a portion of the object moving within the cryostat, since it has a sample holder 1205 clamped thereto and a probe 1206 that moves with the sample holder. The sample holder 1204 includes a first portion 1207 having a first diameter, i.e., a diameter corresponding to the diameter of the contact surface of the first device 1201. The sample holder 1204 also includes a second portion 1208 having a second diameter, i.e., a diameter corresponding to the diameter of the contact surface of the second device 1202.

[0066] The compatibility of the diameter of the sample holder 1204 portion with the diameter of the corresponding contact surface of the cooling device is shown by comparing the first device 1201 and the second device 1202 in the situation shown in FIG. 12 . The sample holder 1204 is positioned where the first device 1201 will cool it. The large-diameter portion 1207 of the sample holder 1204 is pressed against the contact surface of the first device 1201. Based on the principle described above, this means that the heat transfer piece of the first device 1201 is pushed outward from the so-called rest position, where the sample holder 1204 is not positioned. Therefore, the diameter of the first portion 1207 of the sample holder 1201 is not equal to the minimum diameter of the contact surface of the first device 1201 in the rest position. Instead, it is slightly larger so that the sample holder 1201 can move within the first device when the sample holder 1201 pushes the heat transfer piece outward, as shown in FIG. 12 .

[0067] The quantity that is important for heat transfer is not only the force pressing the thermally conductive surfaces together, but also the area of ​​contact. Figure 12 shows how the heat transfer pieces of the first device 1201 are pushed to a position where the majority of the length of each piece contacts the large diameter portion 1207 of the sample holder. This action can be achieved by precisely sizing the structure. Mechanical simulations can be used as an aid to simulate the deformation of the heat transfer pieces and spring pieces and the action of the force pushing the heat transfer pieces and spring pieces outward.

[0068] Correspondingly, the diameter of the second part 1208 of the sample holder 1201 is not equal to the smallest diameter of the contact surface of the second device 1202 in the rest position, but is slightly larger. This is shown in FIG. 12 by vertical dashed lines 1209, 1210 drawn from the lower edge of the second part 1208 to the heat transfer piece of the second device 1202. When the sample holder is lowered the distance from the position shown in FIG. 12 to the position where the second part 1208 is located on the second device 1202, the heat transfer piece of the second device 1202 is in a position similar to that of the heat transfer piece of the first device 1201 in FIG. 12. Immediately after the first part 1207 of the sample holder 1204 is pulled out from it, the heat transfer piece of the first device 1201 naturally returns to its rest position under the pressure of the spring piece of the first part 1201.

[0069] The diameter of the opening 1203 in the cooling structure 108 is larger than the diameter of the portions 1207 or 1208 of the sample holder 1204. This condition is set so that the sample holder 1204 does not touch the edge of the opening 1203 at any stage, but simply moves smoothly through the opening.

[0070] The sample holder 1204 moves to the target area, with the second portion 1208 moving first. To enable this operation, the second portion 1208 must be positioned relative to the first portion 1207 in the same direction as the target area (generally, the second cooling structure 111) relative to the first cooling structure 108. When the second portion 1208 reaches the target area, it has not yet come into contact with any previous portion, and in particular has not slid along any previous contact surface, so it is completely undamaged and unwearable. Each time a sample is changed, two sliding movements (one when the sample is introduced into the target area and the other when the sample is removed from the target area) naturally occur between the second portion 1208 and the contact surface of the second device 1202, but the total amount of these sliding movements is substantially less than if the same portion of the sample holder were to slide over all pre-cooled contact surfaces when introduced and removed.

[0071] When comparing the described embodiment devices with prior art arrangements, such as those shown in FIGS. 4 and 5, one important factor is the thermally conductive cross-sectional area. In prior art arrangements, the spring 402 is typically a gold-coated beryllium copper alloy. Because beryllium copper alloys have poor thermal conductivity at cryogenic temperatures, heat is conducted almost entirely from the sample holder 115 to the flange 105 through the spring's gold coating. While its thickness is typically only a few micrometers, in the devices according to FIGS. 7 and 9-12, the heat transfer element can be solid, highly thermally conductive copper, and in strip-like embodiments, its thickness can be, for example, 0.5 to 1 millimeter. It is therefore clear that the thermally conductive cross-sectional area is several hundred times greater than in prior art solutions.

[0072] The embodiments described herein offer several advantages over providing a thermally conductive coupling from the side of a sample holder or other object moving within a cryostat. One advantage is that they are not sensitive to dimensional changes due to temperature changes. For example, as the probe shortens upon cooling, it moves the sample holder in the same direction as the sample holder moves in any case. This does not significantly change the quality or mechanical compatibility of the thermally conductive coupling between the parts in the above embodiments. Another advantage is that the sample holder may be provided with a fairly large, substantially flat surface (the underside in FIG. 12 ) that is entirely usable for other purposes besides providing a thermally conductive coupling. The surface may be provided with a connector, for example, for transmitting electrical signals, which is pressed into a matching portion within the target area when the sample holder reaches the target area.

[0073] The above exemplary embodiments are not limiting, and many features of the device and arrangement can be implemented in other ways. For example, the device or sample holder need not be rotationally symmetric. Similar principles may also be applied to arrangements in which, for example, the sample holder and the clear shot opening are elliptical, rectangular, or other polygonal. Thus, in such arrangements, the device providing the thermally conductive coupling does not have a rotationally symmetric contact surface, but rather, the contact surface can be formed by, for example, the surface of a heat transfer element facing the opening, linearly arranged on each of the four sides of the rectangular opening. Another example of an extension beyond the above embodiments is that the moving object in the cryostat does not necessarily have to be a sample holder. Similar principles may be applied to, for example, a thermal switch, i.e., a control means for controlling heat transfer between two parts of a cryostat. The moving object is in thermally conductive communication with a first part, and the device according to any of the above embodiments is fastened to a second part. By using some mechanism controlled from outside the cryostat, the moving object may be selectively moved into or out of contact with the contact surface of the device, thus selecting whether or not these two portions of the cryostat are in thermally conductive communication with each other.

Claims

1. 1. An apparatus for providing a thermally conductive coupling for cooling a moving object (601) in a cryostat, comprising: A heat transfer portion (602) that forms a contact surface with the object (601); and means for fastening the heat transfer part (602) to a cooling structure (105, 107, 111, 604) so ​​that the contact surface is free, a spring portion (605) separate from the heat transfer portion (602) and arranged to apply a spring force (606) to the heat transfer portion (602) to urge the contact surface in a direction to bring the contact surface into contact with the object (601); The heat transfer section (602) has a plurality of heat transfer elements (701, 901, 1101) arranged in a ring shape, and the contact surface is formed by the surfaces of the heat transfer elements (701, 901, 1101) facing inward of the ring; The device is characterized in that the spring portion (605) includes one or more spring elements (704, 903, 1102) arranged outside the heat transfer elements (701, 901, 1101) arranged in a ring shape and pushing the heat transfer elements (701, 901, 1101) toward the center of the ring.

2. 2. The apparatus of claim 1, further comprising means (607, 904, 905, 1001, 1103, 1106) for supporting said spring portion (605) to said cooling structure (105, 107, 111, 604).

3. The heat transfer section (602) a clamping ring (1104) having an inner edge; and a plurality of heat transfer pieces (1101) each having one end integrally connected to the inner edge of the clamping ring (1104) and having other free ends oriented in a direction approximately perpendicular to the plane defined by the clamping ring (1104).

4. The spring portion (605) a support ring (1103) fastened to the upper portion of the fastening ring (1104) and having an inner surface; and a plurality of spring pieces (1102) supported on the inner surface of the support ring (1103) and arranged to apply the spring force (606) to the heat transfer piece (1101).

5. 5. The apparatus of claim 4, wherein the spring pieces (1102) form a continuous band extending around the inner surface of the support ring (1103), the band of spring pieces being supported in one or more grooves in the inner surface of the support ring (1103).

6. The apparatus described in claim 4 or 5, further comprising an upper clamping ring (1105) clamped to the upper part of the support ring (1103) and arranged to support the free end of each heat transfer piece (1101) at a position farther from the center line of the ring formed by the heat transfer pieces (1101) than the center of the heat transfer pieces (1101).

7. The device according to any one of claims 1 to 6, characterized in that the heat transfer part (602) is made of copper or silver.

8. 8. The device according to claim 7, characterized in that the heat transfer part (602) made from copper or silver is coated with gold.

9. The device according to any one of the preceding claims, characterized in that the spring portion (605) is made from a beryllium copper alloy.

10. 10. An arrangement for cooling an object in motion in a cryostat, comprising: a cooling structure (105, 107, 108, 111); and a device (1201, 1202) according to any of claims 1 to 9 clamped to the cooling structure.

11. a first cooling structure (108); and a first device (1201) according to any one of claims 1 to 9 fastened to the first cooling structure; a second cooling structure (111) and a second device (1202) according to any one of claims 1 to 9 fastened to the second cooling structure; the first cooling structure (108) includes an opening (1203) concentric with the first and second cooling structures (1201, 1202); In the first device (1201), the contact surface of the device forms a ring having a first diameter; In the second device (1202), the contact surface of the device forms a ring having a second diameter smaller than the first diameter; 11. The arrangement of claim 10, wherein the diameter of the opening (1203) is greater than the first and second diameters.

12. 12. The arrangement of claim 11, wherein the second cooling structure (111) defines a target area to which the object being cooled in the cryostat is fixed.

13. a sample holder (1204) forming at least a portion of the object in motion within the cryostat; the sample holder includes a first portion (1207) having a diameter corresponding to the first diameter; the sample holder includes a second portion (1208) having a diameter corresponding to the second diameter; 13. The arrangement according to claim 11 or 12, characterized in that the second part (1208) is arranged in a part of the sample holder (1204) that is positioned relative to the first part (1207) in the same direction as the second cooling structure (111) that is positioned relative to the first cooling structure (108).

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