RU2254622C1 - Cryogenic entry - Google Patents

Abstract

FIELD: cryogenic engineering; cooling parts to be measured.

SUBSTANCE: proposed cryogenic entry has heat exchanger incorporating part holder. Heat exchanger is disposed in vacuum chamber and communicates with first pipeline for feeding cooling agent and with second pipeline for cooling agent discharge. Pipeline joints in vacuum chamber are made in the form of first and second heat bypasses. Second pipeline is connected to shield. The latter functions to shield first pipeline and heat exchanger, as well as part holder. Heat exchanger incorporates chambers disposed in tandem and separated by perforated walls. First chamber communicates with first pipeline and last chamber, with second pipeline. These chambers are filled with heat-conducting filler in the form of balls. These balls are joined together so that through holes are provided between junction areas. First chamber is filled with balls of diameter d1 and second one, with balls of diameter d2. Joined balls filling first chamber form through holes of area S1 and area of through holes of those filling second chamber is S2, Here d1 < d2 and S1 < S2. Second chamber is provided with third cooling agent feeding pipeline. Part holder is secured on heat exchanger.

EFFECT: improved design.

6 cl, 5 dwg

Description

The device relates to the field of cryogenic technology and can be used to cool measurement objects, for example, in scanning probe microscopy.

Known cryogenic input containing a vacuum chamber in which the holder of the object is connected to a source of refrigerant [1].

The disadvantage of this device is the lack of efficiency in the use of refrigerant, which is associated with a significant magnitude of the path from the object to it.

Also known is a cryogenic inlet located in a vacuum chamber and containing an object holder connected to a heat exchanger that is connected to a first helium supply pipe and a second helium discharge pipe. In this case, the second pipeline is connected to the screen, inside which the first pipeline and the heat exchanger are located. In addition, the first and second pipelines are connected with heat isolation [2].

The first disadvantage of this device is the high helium consumption associated with the relative direct flow of the heat exchanger.

The second drawback is associated with insufficient shielding of the object holder.

All of the above reduces the efficiency of cryogenic input.

The specified device is selected as a prototype of the proposed solution.

The technical result of the invention is to increase the efficiency of cryogenic input.

The specified technical result is achieved in that in a cryogenic inlet containing a heat exchanger with an object holder located in a vacuum chamber, connected to a first refrigerant supply pipe and at least one second refrigerant discharge pipe, which in turn are connected to a refrigerant source located outside the vacuum chamber, and the junction of the pipelines with the vacuum chamber is made in the form of the first and second heat isolation, and the second pipe is connected to the screen, shielding the first pipeline and the heat exchanger, the screen is installed with the possibility of shielding the object holder as well, and the heat exchanger contains working chambers arranged in series and separated by walls with openings, the first chamber being connected to the first pipeline and the last with at least one second pipeline, while the chambers are filled with a heat-conducting filler, and the object holder is mounted directly on the heat exchanger.

There is also an option in which spring clamps are attached to the screen, coupled with the object holder or object, and the heat exchanger is suspended on springs in a vacuum chamber.

It is possible to arrange the openings in the walls between the working chambers in such a way that their passage area increases with distance from the center of the heat exchanger.

In some cases, it is advisable to supply the chambers with partitions that increase the length of the passage opening.

It is also possible to perform a heat-conducting filler in the form of balls interconnected in such a way that through holes exist between the connection zones.

There is also an option in which the object holder is made of sapphire.

There is also an option in which the first chamber is filled with balls with diameters d ₁ forming through holes with each other with area S ₁ , and the second chamber is filled with balls with diameters d ₁ forming through holes with each other with area S ₂ , with d ₁ < d ₂ , a S ₁ <S ₂ , and the second chamber is provided with at least one third pipe for supplying refrigerant.

Figure 1 shows the cryogenic input with a linear sequential arrangement of the working chambers.

In figure 2, 3 - embodiments of the working chambers.

Figure 4 - cryogenic input with a centrally symmetric arrangement of the working chambers.

Figure 5 - cryogenic input with a scanning probe microscope.

The cryogenic input comprises a heat exchanger 1 (Fig. 1) with a holder 2 of object 3 connected to the first pipe 4 for supplying refrigerant and to the second pipe 5 for draining the refrigerant. Pipelines 4 and 5 are connected to a source of refrigerant 6. The source of refrigerant 6 in figure 1 is depicted conditionally. It may contain a refrigerant storage, discharge and collection system.

It should be noted that the proposed cryogenic input is intended for use in a vacuum chamber 7 with pumping means 8.

To ensure the efficient operation of the cryogenic input, the joints of pipelines 4 and 5 with the vacuum chamber 7 are designed in the form of the first and second heat exchangers 9 and 10. Heat exchangers 9 and 10 are usually made of thin-walled stainless tubes connected by plugs and connected at different ends to the vacuum chamber 7 and pipelines 4 and 5. The second pipe 5 is connected by means of a heat-conducting contact with the screen 11, which is arranged to shield the holder 2 of the object 3, the heat exchanger 1 and the first pipe 4. The heat exchanger 1 contains um, for example, the first, second and third working chambers 12, 13 and 14, separated by the first and second walls 15 and 16 with the first and second holes 17 and 18. In this particular embodiment, the first pipe 4 passes through the second chamber 13 and the third the chamber 14 and is connected to the first chamber 12. The chambers 12, 13 and 14 are filled with the first, second and third heat-conducting fillers 19, 20 and 21. The heat exchanger has a heating element 22 and a thermocouple 23 connected to the control unit 24 (see, for example, [3]).

It should be noted that the heat exchanger can be equipped with additional thermocouples (not shown) connected, for example, to the screen 11, to the object 3 from the side of the holder 2 or from the opposite side.

It should be noted that the number of working chambers can vary depending on the size and purpose of the device.

For a more efficient use of the heat exchanger 1, it is possible to fix spring clips 25 connected to the object 3 to the screen 11. If the object 3 is mounted on the holder 2, for example, using cold brazing with indium, the clamps 25 can fix the holder 2.

In addition, it is possible to use a cryogenic input containing a platform 26 connected through heat insulators 27 to a heat exchanger 1 and suspended on springs 28 in a vacuum chamber 7.

It should be noted that the use of springs 28 is often used, because pipelines 4 and 5 are made of thin-walled tubes, the length of which can exceed 10 cm, and have insufficient strength to hold the heat exchanger 1.

In Fig. 1, the holes through which the heat exchanger 1 is installed in the vacuum chamber 7, the loading and unloading of the holder 2 of the object 3, and other technological operations with the object 3 are not shown, the screen 11 should also have an opening with a movable shutter (not shown) for loading and unloading the holder 2 of the object 3.

There is an option in which the passage area of the openings 29, 30 and 31 (FIG. 2) in the walls between the chambers increases with distance from the center of the heat exchanger.

It is also possible the execution of chambers with partitions 32 (figure 3), one ends fixed to the walls and increasing the length of the through hole.

In one embodiment, the filler consists of balls, while the balls can be connected (welded or brazed) together so that there are through holes between the zones of welding or soldering.

There is also an option where the holder 2 of the object 3 is made in the form of a sapphire plate having good thermal conductivity at low temperatures.

In the particular case, the surface of the heat exchanger 1 can be used as a holder 2 for the object 3.

There is also an option in which the first chamber 33 (FIG. 4) is connected, as in the previously described case, to the first pipe 34 and filled with balls 35 with diameters d ₁ . In the wall 36 of a cylindrical shape, holes 37, 38 and 39 are made around the circumference with increasing passage area as you move away from the outlet 40 of the first pipe 34. The second chamber 41 is filled with balls 42 with diameters d ₂ . Balls 35 and 42 form between them through holes with areas S ₁ and S _2, respectively, with d ₁ <d ₂ , a S ₁ <S ₂ . If balls penetrate the openings 37, 38 and 39, the openings may be protected by nets (not shown).

The second chamber 41 is provided with a set of second pipelines 43 for discharging the refrigerant and third pipelines 44 for supplying the refrigerant arranged in a circle. Generally speaking, a simplified version is possible, in which one pipe is used to discharge and supply refrigerant. The described option assumes the presence of two sources of refrigerant. For example, a helium source 45 and a nitrogen source 46. In this case, valves 47, 48, 49 and 50 are included in the cooling system. The nitrogen source 46 comprises a storage system (Duar vessel) and a discharge system made in the form of a nitrogen tank with resistive heating. In the source of helium 45, in addition to the storage system (Duar vessel for helium with a nitrogen jacket) and the discharge system (helium tank with resistive heating), a helium collection system has been introduced. Typically, a helium collection system is a centralized system connected to cryogenic piping (not shown). In figure 1 and figure 4, pipelines for the discharge of spent refrigerant are brought into the source of refrigerant, for example, for its secondary use in order to cool the supply pipelines. In the particular case, the discharge pipes can be connected to the "atmosphere".

A variant of using cryogenic input in scanning probe microscopy is depicted in FIG. 5, where a scanning probe microscope (SPM) 52 is installed on the platform 51 (see, for example, [4, 5]).

SPM 52 is installed using racks 53, which are in interaction with supports 54. In this case, the probe 55 SPM, using the hole 56 in the screen 11, is located with the possibility of interaction with the object 3.

To install the SPM 52 on the platform 51, a quick-detachable flange 58 is usually used in the vacuum chamber 57. Moreover, at the time of installation of the SPM 52, as well as when the holder 2 of the object 3 is replaced, the platform 51 can be fixed relative to the vacuum chamber 57 using an electromagnetic or mechanical grip 59 ( see, for example, [6, 7]). SZM 52 may have a control unit 60, placed outside the walls of the vacuum chamber 57 using a vacuum connector 61. When installing the heat exchanger in the vacuum chamber 57 and to install the holder 2 of the object 3, you can also use the quick-detachable flange 58. However, to install the holder 2 of the object 3, and Also, to replace the probe 55, it is advisable to use a loading device 62 with a manipulator 63, docked to the vacuum chamber 57. For more details on such devices, see [8, 9]. In this case, a hole 64 is made in the screen 11 with a movable shutter 65 driven by the manipulator 63.

In the cryogenic input and its variants described above, the following elements and materials were used.

The vacuum chamber 57 was made of steel 12X18H10T and had a volume of about 30 dm ³ .

As a means of pumping, a turbomolecular pump was used, which provided a pressure in the chamber 57 of the order of 10 ^-6 mm Hg.

Sources of nitrogen and helium were made in the form of cryostats, heat exchangers 9 and 10 were made of steel (12X18H10T) tubes 0.3 mm thick, and pipelines from copper tubes with an outer diameter of 3-5 mm.

The heat exchanger body was made of copper. Balls made of heat-conducting filler steel had a diameter in the range of 1-3 mm.

Screen 11 was made of copper foil, and heat insulators of ceramic and quartz.

Extremely low sample temperature reached 5 K.

The device operates as follows.

After installing the holder 2 of the object 3, using the source 6, for example, liquid helium or nitrogen is fed through a pipe 4 to the first chamber 12. Passing through the holes between the heat-conducting fillers 19, 20 and 21, as well as into the holes 17 and 18 of the walls 15 and 16 , the refrigerant cools the heat exchanger, and then collects through the pipe 5 in the source 6. As a result, the holder 2 with the object 3 is cooled, mounted on the heat exchanger 1. The thermocouple 23 captures the temperature of the holder 2, transmits information to the control unit 24, which by heating ementa 22 has the ability to maintain the temperature of the holder 2 in the desired range. In this case, the screen 11 by means of heat-conducting contact with the pipe 5 shields the heat flux from the walls of the vacuum chamber 7 to the heat exchanger 1, the pipe 4 and the holder 2 with the sample 3.

When using the option shown in figure 2, the refrigerant due to less resistance to its movement through the walls along the edges of the heat exchanger is more evenly distributed over its volume.

The use of partitions 32 (Fig. 3) increases the length of the passage opening and increases the resistance to movement of helium.

The operation of the heat exchanger depicted in figure 4, is as follows. Valves 47 and 48 are opened (valves 49 and 50 are closed at the same time) and, using source 45, liquid helium is supplied to the first chamber 33. First, the movement of helium occurs between balls 35 through openings with areas S ₁ , then through openings 37, 38 and 39 then between the balls 42 through openings with areas S ₂ to the second pipelines 43 through which the helium is returned to the source 45. The dimensions of the openings 37, 38 and 39 are chosen so that the helium flow passes through the openings 37 and 38 and between the balls 35 reaching hole 39.

When the heat exchanger is operating on liquid nitrogen, the valves 47 and 48 are closed and the valves 49 and 50 are opened. After that, using a source 46, nitrogen is supplied through the third pipes 44 to the second chamber 41. In this case, the nitrogen moves between the balls 42 through openings with areas S ₂ to the second pipelines 43, through which nitrogen is returned to the source 46. The movement of nitrogen having a sufficiently high viscosity between the balls 35 through openings with areas S ₁ may not occur, because the value of S _{1 is} optimized for the economical passage of helium having a significantly lower viscosity with respect to nitrogen.

The holder with the object in both cases is mounted on the media in the same way as in FIG. 1.

When using cryogenic input with a scanning probe microscope, the flange 58 is opened (Fig. 5), the shutter 65 is pushed back and the holder 2 with the object 3 is fixed on the heat exchanger 1, ensuring its mechanical contact with the thermocouple 23. After that, the SPM 52 is mounted on the supports 54 of the platform 51. In this case, the probe 55 is located in the hole 56 of the screen 11 with the possibility of interaction with the object 3. It should be noted that it is possible to carry out these operations using the capture 59 with the fixed state of the platform 51. After installing the SPM 52 release the capture 59, the desired temperature is formed on the sample, the probe 55 is connected to the object 3, and its surface is examined. See details in [4, 5]. The probe, as well as the holder 2 of the object 3 can be replaced using the loading device 62 with the manipulator 63 in the fixed state of the platform 51.

The introduction of the screen connected to the second pipeline and located with the possibility of shielding also the holder of the object, increases the efficiency of using cryogenic input.

The implementation of the heat exchanger in the form of a set of working chambers separated by walls with holes and filled with a heat-conducting filler also increases the efficiency of cryogenic input.

The introduction of spring clamps of the object, mounted on the screen and interfaced with the holder of the object or object, optimizes the heat flux between the object and the environment.

Suspension of the heat exchanger on the springs in the vacuum chamber increases the mechanical reliability of the system, and also allows the use of the heat exchanger in probe microscopy, which expands its functionality.

The location of the openings in the walls between the chambers in such a way that the area of their through holes increases with distance from the center of the heat exchanger, more evenly distributes the flows of the refrigerant and improves its cooling.

The supply of working chambers with partitions that increase the length of the bore, allows more efficient use of the coolant. This is especially true for helium having high fluidity.

The implementation of the heat-conducting filler in the form of balls increases the repeatability of the characteristics of cryogenic inputs.

The manufacture of an object holder made of sapphire provides good thermal conductivity at low temperatures and increases the efficiency of using cryogenic input.

The use of two chambers with balls of different diameters allows more efficient use of helium, passing it through the first chamber with balls of small diameter. This is advisable because of the high fluidity of helium, which is irrationally used for large openings between the balls. Nitrogen may not pass through small holes at all, so it is passed through a second chamber with balls of larger diameter.

LITERATURE

1. Japan patent N6 - 208041, 1994.

2. US patent US 4162401, 1979.

3. Temperature control unit with thermocouples.

4. Probe microscopy for biology and medicine. V.A. Bykov et al., Sensory Systems, vol. 12, No. 1, 1998, pp. 99-121.

5. Scanning tunneling and atomic force microscopy in surface electrochemistry. A.I. Danilov, Advances in Chemistry, 64 (8), 1995, p. 818-833.

6. US patent No. 5157256, 1991.

7. Patent RU No. 2158454, 1999.

8. Patent RU No. 2152103, 1996.

9. Patent RU No. 2208845, 2001.

Claims (6)

1. A cryogenic inlet comprising a heat exchanger with an object holder located in a vacuum chamber, connected to a first refrigerant supply pipe and at least one second refrigerant discharge pipe, which, in turn, are connected to a refrigerant source located outside the vacuum the chamber, and the junction of the pipelines with the vacuum chamber is made in the form of the first and second heat decouples, and the second pipeline is connected to the screen screening the first pipe and heat exchanger, characterized the fact that the screen is installed with the possibility of shielding also the holder of the object, and the heat exchanger contains working chambers arranged in series and separated by walls with holes, the first camera being connected to the first pipe and the last with at least one second pipe, the chambers are filled with a heat-conducting filler in the form of balls interconnected in such a way that there are through holes between the connection zones, while the first chamber is filled with balls with diameters d ₁ , the image having through holes with each other with an area of S ₁ , and the second chamber is filled with balls with diameters d ₂ , forming through holes with each other with an area of S ₂ , with d ₁ <d ₂ , a S ₁ <S ₂ , the second camera is equipped with at least one third pipeline for supplying refrigerant, and the object holder is mounted directly on the heat exchanger. 2. The cryogenic input according to claim 1, characterized in that spring clamps are inserted into it, mounted on the screen and paired with an object holder or object. 3. The cryogenic input according to claim 1, characterized in that the heat exchanger is suspended on springs in a vacuum chamber. 4. The cryogenic input according to claim 1, characterized in that the passage area of the holes in the walls between the working chambers increases with distance from the center of the heat exchanger. 5. The cryogenic input according to claim 1, characterized in that the working chambers contain partitions that increase the length of the passage opening. 6. The cryogenic input according to claim 1, characterized in that the object holder is made of sapphire.

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