Low-vibration low-temperature high-intensity magnetic field optical thermostat based on pulse tube refrigerator

Abstract

The low-vibration low-temperature high-magnetic-field optical thermostat comprises a vacuum cavity, a refrigerating machine assembly and a sample cavity assembly, a superconducting magnet surrounds the bottom of the sample cavity assembly, and a primary cold screen is arranged around the refrigerating machine assembly, the sample cavity assembly and the superconducting magnet; the superconducting magnet is provided with an optical channel leading to the sample cavity, a vacuum cavity window and a primary cold screen window are formed in the horizontal position, corresponding to the optical channel, of the vacuum cavity and the primary cold screen, the sample cavity assembly comprises a sample table, and sample cavity windows are formed in the periphery of the sample table in multiple directions. The vibration of the device is greatly reduced, the requirement of optical measurement on low-magnitude vibration amplitude in a low-temperature strong magnetic field environment is met, and meanwhile, the optical observation window and the lifting platform with multiple angles are arranged, so that the observation optical view field is expanded, and a sample is convenient to observe.

Description

TECHNICAL FIELD

[0001] The present application relates to a low-temperature strong magnetic field thermostat, in particular to a low-vibration low-temperature strong magnetic field optical thermostat based on a pulse tube refrigerator. BACKGROUND

[0002] Optical measurement under magnetic field is an important means in physical and chemical research, such as magneto-optical Kerr spectroscopy, infrared and Raman spectroscopy under magnetic field, etc., which application covers superconducting, topological insulator, quantum computing and other basic research and technical fields. In recent years, with the development of frontier technologies such as quantum computing, the demand for sample and device regulation and testing under magnetic field has increased significantly.

[0003] However, it is still difficult to realize optical measurement in a low-temperature strong magnetic field environment. On the one hand, in order to introduce a magnet, the structural size of the cryostat needs to be increased, resulting in an increase in the distance from the external light source to the sample stage, affecting the optical path adjustment and signal collection. On the other hand, in order to conveniently control the temperature of the sample stage, the sample stage needs to be placed in an independent sample chamber. The sample chamber needs to add optical windows, and the fixing method and installation process of the window directly affect the low-temperature stability of the sample stage. In addition, the vibration of the equipment is also crucial to optical measurement, and the vibration amplitude is usually required to be controlled at the nanometer level.

[0004] Both the Gifford-McMahon (GM) type refrigerator and the pulse tube refrigerator can provide refrigeration power at low temperature. Among them, the pulse tube refrigerator separates the main vibration source, the rotating valve, from the refrigerator, which can effectively reduce the system vibration. The vibration amplitude of the refrigeration components is about 1 micrometer, which is one order of magnitude smaller than that of the GM refrigerator. In recent years, with the improvement of the demand for precise measurement, more and more low-temperature thermostats use pulse tube refrigerators instead of GM refrigerators. However, for vibration-sensitive experiments such as optical measurement, the residual vibration of the pulse tube refrigerator will still interfere with signal acquisition, so the vibration reduction structure design is necessary.

[0005] There are two heat exchange structures between the refrigerator and the low-temperature thermostat: coil and low-temperature cooling chamber. The coil refers to the pipeline winding on the heat exchanger of the refrigerator, which realizes the heat exchange between the refrigerator and the low-temperature coolant, and the coolant transfers the cold energy to the sample stage. However, the coil has physical contact with the refrigerator, which will transmit vibration to the sample stage and interfere with the measurement. The other heat exchange structure is to cool the refrigeration working medium by using a low-temperature cooling chamber. The cooling chamber and the refrigerator are in heat transfer through gaseous or liquid working medium, thereby effectively suppressing vibration transmission. By pumping and decompressing the liquid refrigerant medium, low temperature lower than the base temperature of the refrigerator can be obtained in the evaporation chamber through the phase change endothermic process. This kind of decompression usually relies on mechanical valves or capillary tubes to form flow resistance, and both have advantages and disadvantages. Although the existing equipment can realize basic optical measurement function, in actual use, the sample stage still has the problem of relatively large vibration and limited optical field of view, and the stability of its low-temperature performance also needs to be improved. Summary of the Invention

[0006] Purpose of the invention: The purpose of this invention is to provide a low-temperature strong magnetic field optical thermostat with a clear optical field of view, easy observation of samples, and low vibration.

[0007] Technical Solution: The low-vibration, low-temperature, high-magnetic-field optical thermostat based on a pulse tube refrigerator of the present invention includes a vacuum chamber. It is characterized by further including a refrigerator assembly and a sample chamber assembly inside the vacuum chamber. A superconducting magnet surrounds the bottom of the sample chamber assembly. A primary cold screen is arranged around the refrigerator assembly, the sample chamber assembly, and the superconducting magnet. An additional conical cold screen and a sample chamber cold screen are arranged around the sample chamber assembly. The superconducting magnet has an optical channel leading to the sample chamber. A vacuum chamber window and a primary cold screen window are opened at horizontal positions corresponding to the optical channel.

[0008] Preferably, the top of the vacuum chamber is sealed by a vacuum chamber flange, and the refrigeration unit includes at least one combination of a pulse tube refrigeration unit and a heat exchanger. The flange of the refrigeration unit is connected to the vacuum chamber flange by a shock-absorbing spring.

[0009] Preferably, the sample chamber assembly includes a sample stage, and sample chamber windows are provided in at least four directions around the sample stage.

[0010] Preferably, the sample chamber window is adhered to a window bracket, and the window bracket is fixedly connected to the sample chamber observation stage.

[0011] Preferably, the sample chamber assembly includes an outer sample chamber and an inner sample chamber, the outer sample chamber and the inner sample chamber forming an annular cavity, an air inlet at the bottom of the annular cavity and an air outlet at the top, the air outlet being connected to a circulating dry pump, and the other side of the circulating dry pump being connected to a refrigeration unit through a low-temperature cooling chamber air inlet.

[0012] Preferably, the sample chamber includes at least one heat-insulating radiation screen inside.

[0013] Preferably, the sample chamber contains a sample rod, the bottom of which is connected to a sample stage, and the top of which is connected to a vacuum lifting device.

[0014] Preferably, the lifting device is connected to the upper wall of the sample chamber via a shock-absorbing bellows, and the upper and lower parts of the shock-absorbing bellows are padded with rubber pads.

[0015] Preferably, the bottom pipe of the refrigeration unit is connected to the low-temperature valve chamber, the low-temperature valve chamber includes a low-temperature valve needle, and the liquid inlet of the coil on the other side of the low-temperature valve chamber is connected to the coil.

[0016] Preferably, the vacuum cavity is placed on a vibration-damping optical platform with a rotating bearing.

[0017] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: 1. By setting up multi-level shock absorption components, the vibration of the device is greatly reduced; 2. Multiple optical observation windows are set up and connected by window brackets, which provides a clear optical field of view and improves the sealing performance of the windows. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the overall structure of the present invention;

[0019] Figure 2 This is a schematic diagram of the middle section of the sample chamber of the present invention;

[0020] Figure 3 This is a schematic diagram of the sample stage of the present invention. Detailed Implementation

[0021] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0022] As shown in the attached diagram, this embodiment provides a low-vibration, low-temperature, high-magnetic-field optical thermostat based on a pulse tube refrigerator, comprising: 1-pulse tube refrigerator cold head, 2-damping spring, 3-folded edge, 4-upper wall of the low-temperature cooling chamber, 5-first-stage pulse tube, 6-first-stage pulse tube cold head, 7-first-stage heat exchanger, 8-second-stage pulse tube, 9-lower wall of the low-temperature cooling chamber, 10-second-stage pulse tube cold head, 11-second-stage heat exchanger, 12-low-temperature cooling chamber chassis, 13-refrigeration unit assembly, 14-low-temperature valve room temperature adjustment rod, 15-valve stem, 16-first-stage cold sink of the low-temperature valve, 17-valve cavity, 18-valve needle, 19-low-temperature valve inlet, 20-low-temperature valve outlet, 21-coil inlet, 22-vacuum chamber flange, 23-vacuum chamber, 24-... Vacuum chamber window, 25-support rod, 26-first-stage cold plate, 27-first-stage cold screen, 28-first-stage cold screen window, 29-conical cold screen, 30-sample chamber cold screen, 31-magnetic cooling plate, 32-superconducting magnet, 33-lifting platform, 34-vibration damping bellows, 35-sample chamber inner cavity, 36-sample chamber inner cavity air extraction port, 37-sample chamber outer cavity, 38-annular cavity air outlet, 39-vacuum dry pump, 40-low temperature cooling chamber air inlet, 41-heat insulation radiation screen, 42-sample chamber window, 43-sample stage, 44-annular cavity air inlet, 45-coil, 46-lower section of sample chamber inner cavity, 47-window bracket, 48-sample chamber observation platform, 49-bottom section of sample chamber inner cavity, 50-sample chamber assembly.

[0023] The cryostat mainly consists of a refrigeration system assembly, a sample chamber assembly, and a superconducting magnet. The refrigerator provides all the necessary cooling capacity to the cryostat. The superconducting magnet is directly connected to the bottom of the refrigeration system assembly via high-purity oxygen-free copper. The refrigeration assembly mainly comprises a cold head, an upper wall of the cryogenic cooling chamber, a lower wall of the cryogenic cooling chamber, and a base plate. The refrigerator uses a pulse tube refrigerator to accommodate optical measurements. At least one air inlet is located at the top of the refrigeration assembly for supplying the cooling medium.

[0024] A folded edge structure is installed below the air inlet to reduce the heat radiation from the damping bellows at room temperature to the refrigerator. Similarly, a folded edge structure is installed at the location of the first-stage heat exchanger to reduce the heat radiation from the first-stage cold plate to the first-stage cold head. In the low-temperature cooling chamber, the refrigerant exchanges heat with the first-stage and second-stage cold heads of the refrigerator, respectively, and transfers the cooling capacity to the first-stage and second-stage heat exchangers.

[0025] The superconducting magnet is connected to the bottom of the cryogenic cooling chamber for direct heat exchange. Simultaneously, the superconducting magnet can be fixed to the bottom of the cryogenic cooling chamber. In this embodiment, the superconducting magnet is quadrilateral, with four channels in the horizontal direction and two channels in the vertical direction. The vertical channels are used to place the sample chamber, and the horizontal channels are used to observe the sample chamber. It should be noted that, in addition to quadrilaterals, the superconducting magnet can also adopt other polygonal configurations, such as triangles, pentagons, hexagons, heptagons, octagons, etc. Each side can be configured with a window, and a corresponding window is configured for the sample chamber.

[0026] The sample chamber is divided into two parts: an inner sample chamber and an outer sample chamber. The area enclosed by the inner and outer sample chambers is usually called an annular cavity. The refrigerant, after liquefying in the cryogenic cooling chamber, is collected at the bottom. Due to the pressure difference generated by the dry pump, the liquid coolant flows directionally to the cryogenic valve. In this embodiment, a cryogenic valve is used as the source of flow resistance; a capillary tube can also be used instead. After passing through the cryogenic valve, the liquid coolant enters the coiled tube at a lower temperature from the inlet. The coiled tube is soldered to the lower section of the inner sample chamber for heat exchange. The lower section of the inner sample chamber transfers the cold energy to the sample stage via an exchange gas. To enhance cold energy transfer, both the coiled tube and the lower section of the inner sample chamber are made of oxygen-free copper with high thermal conductivity.

[0027] The coolant then enters the annular cavity formed by the upper section of the inner tube and the outer tube of the sample chamber through the inlet, continuing to exchange heat with the upper section of the inner tube. The upper section of the inner tube is made of thin-walled stainless steel to reduce heat leakage in this section.

[0028] The lower section of the sample chamber, the observation stage of the sample chamber, and the bottom section of the sample chamber are bonded together using low-temperature adhesive. An optically transparent window is bonded to a U-shaped titanium alloy support, which is then bonded to the observation stage of the sample chamber.

[0029] The purpose of dividing the sample chamber into three sections is to bond the observation window to the observation stage from the inside. In actual operation, the inside of the sample chamber tube is in an exchange gas environment with a pressure of 10 kPa, while the outside of the sample chamber is in a vacuum environment. Therefore, the window support is subjected to an outward force, which helps to tighten the window support to the observation stage and increase the stability of the sample chamber. The commonly used low-temperature adhesive is Stycast 1266, a transparent epoxy resin with excellent flowability, making it easier to fill gaps.

[0030] The purpose of bonding the optically transparent window to the U-shaped titanium alloy bracket is to avoid a significant difference in the coefficients of thermal expansion between the non-metallic transparent window and the metallic sample chamber observation stage. At low temperatures, due to the thermal expansion and contraction effect, metallic materials shrink more, which can increase the leakage rate of a normally leak-proof interface, affecting the use of the equipment. Using a U-shaped titanium alloy window bracket acts as a buffer zone for the shrinkage of the sample chamber observation stage caused by thermal expansion and contraction. This ensures that both the non-metallic window and the metallic sample chamber observation stage are tightly bonded to the window bracket and remain unaffected by temperature changes.

[0031] The damping bellows decouples the sample rod from the sample chamber, preventing vibrations from being transmitted to the sample stage. The lifting platform is used to adjust the vertical position of the sample stage, increasing the measurement range.

[0032] Primary cold shields, primary cold shield windows, and conical cold shields are used to isolate the superconducting magnet from radiative heat leakage by the vacuum cavity at room temperature. The conical surface of the cold shield extends to the magnet surface to increase the viewing angle of the sample cavity. Sample cavity cold shields isolate the superconducting magnet from radiative heat leakage by the variable-temperature sample cavity. The sample cavity cold shield has channels at corresponding positions in the sample cavity window.

[0033] The vacuum chamber is equipped with four transparent optical windows, each located in one of the four directions corresponding to the sample chamber. The windows are secured to the vacuum chamber using O-rings. The vacuum chamber also features optical mounting holes for mounting on an optical platform and a rotary bearing, allowing for multi-angle observation of the sample through rotation.

Claims

1. A low-vibration, low-temperature, high-magnetic-field optical thermostat based on a pulse tube refrigerator, comprising a vacuum chamber (23), characterized in that, It also includes a refrigerator assembly (13) and a sample chamber assembly (50) inside the vacuum chamber (23). The bottom of the sample chamber assembly (50) is surrounded by a superconducting magnet (32). A primary cold screen (27) is provided around the refrigerator assembly (13), the sample chamber assembly (50) and the superconducting magnet (32). A conical cold screen (29) and a sample chamber cold screen (30) are additionally provided around the sample chamber assembly (50). The superconducting magnet (32) has an optical channel leading to the sample chamber (50). The vacuum chamber (23) and the primary cold screen (27) have a vacuum chamber window (24) and a primary cold screen window (28) at the horizontal position corresponding to the optical channel.

2. The low-vibration, low-temperature, high-magnetic-field optical thermostat based on a pulse tube refrigerator according to claim 1, characterized in that, The top of the vacuum chamber (23) is sealed by the vacuum chamber flange (22). The refrigeration unit (13) includes at least one pulse tube refrigeration cold head (1) and heat exchanger (7). The flange of the refrigeration unit (13) is connected to the vacuum chamber flange (22) by a shock-absorbing spring (2).

3. The low-vibration, low-temperature, high-magnetic-field optical thermostat based on a pulse tube refrigerator according to claim 1, characterized in that, The sample chamber assembly (50) includes a sample stage (43) with sample chamber windows (42) in at least four directions around the sample stage (43).

4. The low-vibration, low-temperature, high-magnetic-field optical thermostat based on a pulse tube refrigerator according to claim 3, characterized in that, The sample chamber window (42) is bonded to the window bracket (47), and the window bracket (47) is fixedly connected to the sample chamber observation stage (48).

5. The low-vibration, low-temperature, high-magnetic-field optical thermostat based on a pulse tube refrigerator according to claim 1, characterized in that, The sample chamber assembly (50) includes an outer sample chamber (37) and an inner sample chamber (35). The outer sample chamber (37) and the inner sample chamber (35) form an annular cavity. An air inlet (46) is provided at the bottom of the annular cavity and an air outlet (38) is provided at the top. A circulating dry pump (39) is connected to the air outlet (38). The other side of the circulating dry pump (39) is connected to the refrigeration unit (13) through the air inlet (40) of the low temperature cooling chamber.

6. The low-vibration, low-temperature, high-magnetic-field optical thermostat based on a pulse tube refrigerator according to claim 5, characterized in that, The sample chamber (35) includes at least one heat-insulating radiation screen (41).

7. The low-vibration, low-temperature, high-magnetic-field optical thermostat based on a pulse tube refrigerator according to claim 5, characterized in that, The sample chamber (35) contains a sample rod, the bottom of which is connected to the sample stage (43), and the top of which is connected to a vacuum lifting device (33).

8. The low-vibration, low-temperature, high-magnetic-field optical thermostat based on a pulse tube refrigerator according to claim 7, characterized in that, The lifting device (33) is connected to the upper wall of the sample chamber (35) through a shock-absorbing corrugated pipe (34), and the upper and lower parts of the shock-absorbing corrugated pipe (34) are padded with rubber pads.

9. The low-vibration, low-temperature, high-magnetic-field optical thermostat based on a pulse tube refrigerator according to claim 1, characterized in that, The bottom pipe of the refrigeration unit (13) is connected to the low temperature valve chamber (17), and the low temperature valve chamber (17) includes a low temperature valve needle (18). The coil inlet (21) on the other side of the low temperature valve chamber (17) is connected to the coil (45).

10. The low-vibration, low-temperature, high-magnetic-field optical thermostat based on a pulse tube refrigerator according to claim 1, characterized in that, The vacuum cavity (23) is placed on a shock-absorbing optical platform with a rotating bearing.

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