Magnetocaloric Cooling Component for Space Ultra-Cold Atomic Physics Experiments and Its Preparation Method

Abstract

A magnetic refrigeration component for space ultra-cold atom physics experiments, comprising a pair of Helmholtz coils, a heat pipe, a phase change cold plate, and a heat conduction housing composed of a coil housing and a heat pipe housing; the coils are formed on a coil skeleton, the evaporation end of the heat pipe is sleeved on the outer side of the coil, the coil housing is sleeved outside the evaporation end of the heat pipe, and the heat pipe housing is sleeved outside the coil housing; the condensation end of the heat pipe is attached to the phase change cold plate; the heat generated by the coils is conducted to the surface of the heat conduction housing, and then absorbed and phase-changed by the evaporation end of the heat pipe, and the heat is conducted to the condensation end of the heat pipe and absorbed and dissipated by the phase change plate. This magnetic refrigeration system can ensure that the temperature on the surface of the coils is within the required range during the working state. The magnetic refrigeration component provided by the present invention has a compact structure, with a total weight of only about 10 kg, and has strong universality, and can be directly promoted for use in space missions or productized cold atom experimental systems.

Description

Technical Field

[0001] The present invention relates to magnetic field generation and corresponding thermal control technologies, and particularly to a magnetic-thermal cooling component for space ultra-cold atom physics experiments and a preparation method thereof. Background Art

[0002] The development of cold atom physics and corresponding technologies enables people to prepare atomic samples with temperatures as low as nano-Kelvin. Such quantum gases can be applied to various research fields such as precision measurement, quantum simulation, and quantum thermodynamics based on quantum technologies.

[0003] The usual technical route for obtaining ultra-cold atomic gases is as follows: A two-dimensional magneto-optical trap is used to pre-cool the background vapor to obtain an atomic beam, which is then injected into a three-dimensional magneto-optical trap (3D-MOT). After that, further cooling is carried out through methods such as polarization gradient cooling, and then it is loaded into a quadrupole magnetic trap for evaporative cooling. In both the 3D-MOT and quadrupole magnetic trap stages, a pair of anti-Helmholtz coils are required to construct a quadrupole magnetic field. Usually, the 3D-MOT lasts for about 10 s, and the required axial magnetic field gradient is about 0.15 mT / mm. For the magnetic trap evaporative cooling stage, it needs to last for 10 to 20 s, and the required axial magnetic field gradient has to reach 1.5 mT / mm to effectively trap atoms. For certain types of ultra-cold physics experiments, the coil pair needs to be passed with a co-directional current to generate a uniform magnetic field on the order of 10 mT, so as to adjust the interaction strength between atoms through the magnetic Feshbach resonance effect.

[0004] For a conventional cold atom experimental system, the average heat dissipation of the coil under long-term operation is about several hundred watts. For such heat dissipation, in order to prevent heat accumulation from causing the coil temperature to be too high and damaging the vacuum system of the cold atom science cavity, active heat dissipation must be carried out. For conventional ground experiments, rectangular copper wires with water flowing through the center are generally used to wind the magnetic field coils. However, such coils are very heavy and it is difficult to apply them to cold atom physics systems with high requirements for structural compactness. Moreover, the micro-vibrations brought about by water-cooled heat dissipation will affect the heating of atoms and the experimental results. Summary of the Invention

[0005] The purpose of the present invention is to overcome the deficiencies of the above-mentioned prior art, and provide a magnetic-thermal cooling component for cold atom physics experiments and a preparation method thereof. The magnetic field generation part of the magnetic-thermal cooling component can provide the magnetic field configuration required for cold atom experiments, and the instantaneous heat exchange capacity of the active heat dissipation part in a single experimental cycle is greater than the average heat dissipation of the coil, so as to control the surface temperature of the magnetic field generation coil within a reasonable range and meet the requirements of the space ultra-cold atom physics experimental device.

[0006] The technical solution of the present invention is as follows:

[0007] A magnetocaloric cooling assembly for space ultracold atomic physics experiments, comprising a pair of Helmholtz coils for providing a quadrupole magnetic field and a uniform magnetic field distribution required for cold atom experiments, and characterized in that it also comprises a heat pipe, a phase change cold plate, and a heat conductive shell composed of a coil shell and a heat pipe shell;

[0008] The coil is formed on a coil skeleton, the evaporation end of the heat pipe is sleeved on the outer side of the coil, the coil shell is sleeved outside the evaporation end of the heat pipe, and thermal conductive silicone grease is applied between the heat pipe and the coil shell, and cold welding is adopted between the coil shell and the coil skeleton; the heat pipe shell is sleeved outside the coil shell, and the heat pipe shell and the coil shell are fixed by cold welding to compress the evaporation end of the heat pipe; the condensation end of the heat pipe is attached to the phase change cold plate; the heat generated by the coil is conducted to the surface of the heat conductive shell, and then the evaporation end of the heat pipe absorbs heat and undergoes phase change, and the heat is conducted to the condensation end of the heat pipe, and the phase change plate absorbs and dissipates the heat.

[0009] The Helmholtz coil is made by selecting a coil frame slightly larger than the coil size and winding the enameled wire on the frame according to the coil design parameters. The coil pair can provide the quadrupole magnetic field required for the magneto-optical trap and the magnetic trap by passing equal-large reverse currents, and can provide the uniform magnetic field required for adjusting the interaction strength between atoms by using the magnetic Feshbach resonance effect by passing equal-large forward currents.

[0010] The heat-conducting shell is composed of a coil shell and a heat pipe shell. Its main function is to conduct the heat generated by the coil when it is working to the shell surface, ensuring that the surface temperature of the coil is within the set range so that it can work normally. The material of the heat-conducting shell is aluminum alloy 6061 state T6, which has the characteristics of high strength and light weight.

[0011] The main function of the heat pipe is to absorb the heat conducted by the heat-conducting shell, and conduct the heat to the condensing end of the heat pipe through the heat absorption phase change of the evaporation end of the internal working fluid. The heat pipe is an aluminum-ammonia heat pipe, which can meet the needs.

[0012] The main function of the phase change cold plate is to absorb the heat conducted by the heat pipe to ensure the normal operation of the heat pipe. The shell material of the phase change cold plate is aluminum alloy 3A21, which has excellent thermal conductivity and brazing performance. As the core component of the magnetocaloric cooling assembly, the specific structure and parameter design of the phase change cold plate needs to match the system requirements, as follows:

[0013] 1) Phase change cold plate structure. The phase change cold plate is composed of a cover plate, a bottom plate, fins and a filling pipe, and a filling port is reserved. The phase change cold plate adopts a fin structure. The fin is the basic component of the plate-fin phase change plate. The heat transfer process is mainly completed through the heat conduction of the fins, so the selection of the form of the phase change plate fins is very important. The magnetic thermal cooling assembly described in the present invention uses serrated fins with good thermal conductivity and strength effects, which does not affect the filling of the phase change medium. The serrated fin belongs to the interrupted fin surface, which is characterized by interrupting the wall surface, so that no thick boundary layer will appear, and the flow at each interruption is uniformly developed, so its heat exchange capacity is greatly improved, and its surface heat transfer coefficient is more than twice that of the general triangular fins and rectangular fins.

[0014] 2) Phase change material. The working principle of the phase change plate is to absorb a large amount of latent heat when the phase change material melts, and release a large amount of latent heat when solidified. Since the phase change thermal control device only undergoes a change in physical state, has no moving parts, consumes no energy, and has high reliability, it is particularly suitable for temperature control of high-power instruments and equipment that work periodically in spacecraft or equipment affected by periodic high heat flow. The present invention selects n-octadecane as the phase change material. Such an organic phase change material has good solid formability, is not prone to phase separation and supercooling, has low vapor pressure when melted, is non-toxic, non-corrosive, self-nucleating, and has stable performance. The phase change temperature of n-octadecane is 28°C, the latent heat of phase change is 242.22 kJ / kg, and the density is 777 kg / m 3 Assuming that the total heat generated by the two coils in a single working cycle is 6000 J, the required volume of n-octadecane is: V = 6000 / (242440 × 777 × 10 6 )=32mL. The internal volume of the phase change cold plate is about 400mL. It is expected that the phase change cold plate can work continuously for 12 cycles without water cooling. When connected to water cooling, the phase change cold plate can support the system to remain in working state for a long time.

[0015] 3) Phase change cold plate pressure analysis. The cover thickness of the phase change cold plate is δ p =1mm, fin spacing s f =2.8mm, fin thickness 0.2mm, and design pressure 0.4MPa. Tensile strength at room temperatureσ b =110MPa, yield strength σ 0.2 =40MPa, then the allowable stress is σ b / n b and σ 0.2 / n s The minimum value of the aluminum alloy 3A21, its safety factor is n b =3,n s =1.5, so the allowable stress of the material is [σ] = 26.6MPa. The pressure bearing capacity of the phase change cold plate meets If the maximum additional amount C = 0.05 mm is taken, then P = 4 MPa, which is much greater than the internal working pressure. Therefore, the phase change cold plate has excellent pressure-bearing capacity.

[0016] The above design and analysis of the phase change cold plate can be directly extended to the parameter design of other cold atom physics experiment magnetocaloric cooling components of the same type.

[0017] The preparation process of the entire magnetocaloric cooling component is roughly as follows: First, wind the coil on the coil skeleton. Apply thermal conductive adhesive to the upper surface and side arc surface of the coil shell and the coil. Fix the coil shell and the coil skeleton by cold spot welding. After forming, install the heat pipe on the outer side of the coil. Apply thermal conductive silicone grease between the heat pipe and the coil shell. Fix the heat pipe shell and the coil shell by cold spot welding to press the heat pipe. The heat conductive material filled inside the heat conductive shell is selected as heat conductive silicone rubber, which is a heat conductive, room temperature curing silicone bonding and sealing adhesive. After the installation of the heat pipe and the coil shell is completed, two coil heat pipe components are formed, and then they are installed with the phase change cold plate. When installing, it is required that the heat pipe is horizontal. Calibrate the heat pipe with a level and adjust the levelness with a heat pipe pressing plate. Apply thermal conductive adhesive to the installation contact surface between the heat pipe and the phase change cold plate, and press the heat pipe with a pressing plate to ensure that the heat pipe is closely attached to the phase change cold plate.

[0018] Compared with the coil and heat dissipation system of cold atom physics experiments in the ground conventional laboratory environment, the magnetocaloric cooling component designed by the present invention is more compact and reliable, and thus can be applied to space missions and productized cold atom physics systems. Specifically:

[0019] 1) Sealing performance. The shell is sealed by cold welding. Cold welding has the characteristics of low welding temperature, can be directly touched by hand after welding, and the temperature after welding is lower than the coil tolerance temperature (the coil tolerance temperature is 130 - 220 °C), and the sealing performance after welding is excellent, meeting the requirements of space missions.

[0020] 2) Structural strength. The heat pipe is buried in the shell groove and fixed by thermal conductive adhesive, which does not damage the heat pipe structure and does not affect the sealing performance and structural strength of the heat pipe. The outer shell of the heat pipe is fixed by spot welding, having good structural strength.

[0021] 3) Heat transfer performance. Each coil exchanges heat with the phase change cold plate through an independent heat pipe. It can be known through thermal simulation that it can meet the heat transfer requirements, thus ensuring the normal operation of the coil.

[0022] 4) Weight. The total weight of the entire magnetocaloric cooling component can be controlled at about 10 kg, and its weight is greatly reduced compared with the coil and heat dissipation system of cold atom physics experiments in the conventional laboratory environment. Description of the Drawings

[0023] Figure 1 is the overall layout diagram of the magnetocaloric cooling component for space ultra-cold atom physics experiments of the present invention

[0024] Figure 2 is an exploded view of the installation layout of the heat pipe and the heat conduction housing

[0025] Figure 3 is a sectional view of the heat pipe installation

[0026] Figure 4 is a schematic diagram of the structure of the phase change cold plate

[0027] In the figure: 1 - science cavity; 2 - coil housing; 3 - coil skeleton; 4 - heat pipe housing; 5 - heat pipe; 6 - phase change cold plate; 7 - filling pipe; 8 - pressing plate; 9 - coil; 10 - cover plate; 11 - fin; 12 - bottom plate; 13 - cold solder spot welding fixation. Specific implementation manners

[0028] The present invention will be further described below in conjunction with the implementation examples and the drawings, but the protection scope of the present invention should not be limited thereby.

[0029] Refer to Figure 1 Figure 1 is the overall layout diagram of the magnetocaloric cooling component for space ultra - cold atom physics experiments of the present invention. As shown in the figure, a magnetocaloric cooling component for space ultra - cold atom physics experiments includes a pair of Helmholtz coils 9 for providing the quadrupole magnetic field and uniform magnetic field distribution required for cold atom experiments, and also includes a heat pipe 5, a phase change cold plate 6, and a heat conduction housing composed of a coil housing 2 and a heat pipe housing 4. The coil 9 is formed on the coil skeleton 3. The evaporation end of the heat pipe 5 is sleeved on the outer side surface of the coil 9. The coil housing 2 is sleeved outside the evaporation end of the heat pipe 5, and thermal conductive silicone grease is applied between the heat pipe 5 and the coil housing 2. The coil housing 2 and the coil skeleton 3 are cold - soldered; the heat pipe housing 4 is sleeved outside the coil housing 2, and the heat pipe housing 4 and the coil housing 2 are cold - soldered and fixed to press the evaporation end of the heat pipe 5; the condensation end of the heat pipe 5 is attached to the phase change cold plate 6; the heat generated by the coil is conducted to the surface of the heat conduction housing, and then the evaporation end of the heat pipe absorbs heat and undergoes a phase change, conducting the heat to the condensation end of the heat pipe, and the phase change plate absorbs and dissipates the heat.

[0030] The Helmholtz coil is made by selecting a coil skeleton slightly larger than the coil size and winding it on the skeleton with enameled wire according to the coil design parameters. The coil pair can provide the quadrupole magnetic field required by the magneto-optical trap and the magnetic trap by passing equal large reverse currents, and can provide the uniform magnetic field required to adjust the interaction strength between atoms by using the magnetic Feshbach resonance effect by passing equal large forward currents. The active heat dissipation part mainly includes: heat-conducting shell, heat pipe and phase change cold plate. The instantaneous heat exchange capacity of a single experimental cycle is greater than the average heat consumption of the coil, so that the surface temperature of the magnetic field generating coil can be controlled within a reasonable range to meet the needs of space ultracold atomic physics experimental devices. Specifically, the heat-conducting shell is composed of a coil shell and a heat pipe shell. Its main function is to conduct the heat generated by the coil when it is working to the shell surface, ensuring that the surface temperature of the coil is within the set range so that it can work normally. The material of the heat-conducting shell is aluminum alloy 6061 state T6, which has the characteristics of high strength and light weight; the main function of the heat pipe is to absorb the heat conducted by the heat-conducting shell, and conduct the heat to the condensation end of the heat pipe through the endothermic phase change of the internal working fluid at the evaporation end. The heat pipe is made of aluminum-ammonia heat pipe, which can meet the demand; the main function of the phase change cold plate is to absorb the heat conducted by the heat pipe to ensure the normal operation of the heat pipe. The shell material of the phase change cold plate is made of aluminum alloy 3A21, which has excellent thermal conductivity and brazing performance.

[0031] See also Figure 2 , 3. They are respectively the exploded view of the installation layout of the heat pipe and the heat-conducting shell and the cross-sectional view of the heat pipe installation. The preparation process of the entire magnetic thermal cooling assembly is as follows: first, the coil is wound on the coil skeleton, and the coil shell and the upper surface and side arc surface of the coil are coated with thermal conductive glue. The coil shell and the coil skeleton are fixed by cold welding spot welding. After forming, the heat pipe is installed on the outer side of the coil, and thermal conductive silicone grease is applied between the heat pipe and the coil shell. The heat pipe shell and the coil shell are fixed by cold welding spot welding to press the heat pipe. The heat-conducting material filled inside the heat-conducting shell is thermal conductive silicone rubber, which is a thermal conductive, room temperature curing silicone adhesive sealant. After the heat pipe and the coil shell are installed, two coil heat pipe assemblies are formed, and then installed with the phase change cold plate. The heat pipe is required to be horizontal during installation. The heat pipe is calibrated with a level and the heat pipe is adjusted with a heat pipe pressing plate. The contact surface of the heat pipe and the phase change cold plate is coated with thermal conductive glue, and the heat pipe is pressed with a pressing plate to ensure that the heat pipe and the phase change cold plate fit tightly.

[0032] See also Figure 4 . Figure 4It is a schematic diagram of the structure of a phase change cold plate. The phase change cold plate is composed of a cover plate, a bottom plate, fins and a filling pipe, with a filling port reserved. The phase change cold plate adopts a fin structure. The fins are the basic components of the plate-fin type phase change plate, and the heat transfer process is mainly completed through the heat conduction of the fins. The serrated fins with good heat conduction and strength effects are selected for the magnetocaloric cooling component described in the present invention, which does not affect the filling of the phase change medium, and its surface heat transfer coefficient is more than twice that of the general triangular fins and rectangular fins; the phase change cold plate selects n-octadecane as the phase change material. According to the heat dissipation capacity of n-octadecane and the system parameters, the phase change cold plate with an internal volume of about 400 mL is expected to support the continuous operation of the system for 12 cycles without connecting water cooling. Under the condition of connecting water cooling, the phase change cold plate can support the system to be in a working state for a long time; reasonable parameter design can make the pressure-bearing capacity of the phase change cold plate much greater than its internal working pressure. The design and analysis of the phase change cold plate can be directly extended to the parameter design of other magnetocaloric cooling components of the same type of cold atom physics experiments.

[0033] In practical applications, the splicing of the housing of the magnetocaloric cooling component involved in the present invention mainly adopts cold welding. After welding, the sealing performance is excellent and it has good structural strength. The heat pipe is buried in the housing groove and fixed by heat-conducting glue, so the structure is very compact and the heat transfer efficiency is excellent. At the same time, since the water-cooled part is far away from the science cavity where precise atomic experiments are carried out, the influence of micro-vibration on the experimental results can be greatly reduced. The integrated design enables the total weight of the entire magnetocaloric cooling component to be controlled at about 10 kg. Compared with the coils and heat dissipation systems of cold atom physics experiments in a conventional laboratory environment, its weight is greatly reduced, and it is very compact and reliable. Such design features are very conducive to applications in space missions and productized cold atom physics systems, such as space atom interferometers and ground-portable atomic gyroscopes.

Claims

1. A magnetocaloric cooling component for space ultracold atom physics experiments, comprising a pair of Helmholtz coils (9) for providing a quadrupole magnetic field required for cold atom experiments and a uniform magnetic field distribution, characterized in that, It also includes a heat pipe (5), a phase change cold plate (6), and a heat conduction housing composed of a coil housing (2) and a heat pipe housing (4); The coil (9) is formed on a coil skeleton (3). The evaporation end of the heat pipe (5) is sleeved on the outer side of the coil (9). The coil housing (2) is sleeved on the evaporation end of the heat pipe (5), and thermal conductive silicone grease is applied between the heat pipe (5) and the coil housing (2). The coil housing (2) and the coil skeleton (3) are fixed by cold solder welding. The heat pipe housing (4) is sleeved on the outside of the coil housing (2), and the heat pipe housing (4) and the coil housing (2) are fixed by cold solder welding to compress the evaporation end of the heat pipe (5). The condensation end of the heat pipe (5) is attached to the phase change cold plate (6). The heat generated by the coil is conducted to the surface of the heat conduction housing, and then absorbed by the evaporation end of the heat pipe for phase change, and the heat is conducted to the condensation end of the heat pipe, and dissipated by the phase change plate.

2. The magnetothermal cooling component for space ultracold atom physics experiments according to claim 1, wherein Thermal conductive glue is applied to the installation contact surface between the heat pipe (5) and the phase change cold plate (6).

3. The magnetocaloric cooling component for space ultra-cold atom physics experiments according to claim 1, characterized in that The coil (9) is wound on a coil skeleton (3) that is slightly larger than the coil size according to the coil design parameters using enameled wire. The coil provides the magnetic field distribution required for experiments at the center of the scientific cavity (1).

4. The magnetothermal cooling component for space ultracold atomic physics experiments according to claim 1, characterized in that, The materials of the coil housing (2) and the heat pipe housing (4) are both selected as aluminum alloy 6061 in the T6 state.

5. The magnetocaloric cooling component for space ultracold atomic physics experiments according to claim 1, wherein The phase change cold plate (6) consists of a cover plate (10), a bottom plate (12), fins (11), and a filling tube (7). A filling port is reserved. The phase change medium inside the phase change cold plate (6) is selected as n-octadecane, which is stable under normal temperature and pressure.

6. The magnetocaloric cooling assembly for space ultracold atom physics experiments according to claim 5, characterized in that, For the installation of the heat pipe (5) and the phase change cold plate (6), it is required that the heat pipe (5) be horizontal. The heat pipe (5) is calibrated with a level, the levelness is adjusted with a heat pipe pressing plate, and the heat pipe (5) is pressed by the bottom plate (12) to ensure that the heat pipe (5) is closely attached to the phase change cold plate (6).

7. The magnetocaloric cooling component for space ultracold atom physics experiments according to claim 1, characterized in that, The heat conduction material filled inside the heat conduction housing is selected as thermal conductive silicone rubber, which is a thermal conductive, room temperature curing silicone bonding and sealing adhesive.

8. A method for a magnetocaloric cooling component used in a space ultracold atom physics experiment, characterized in that, It includes the following steps: After the coil is wound on the coil skeleton, thermal conductive glue is applied to the upper surface and the side arc surface of the coil and the coil housing. The coil housing and the coil skeleton are fixed by cold solder welding. After forming, the heat pipe is installed on the outer side of the coil, thermal conductive silicone grease is applied between the heat pipe and the coil housing, and the heat pipe housing and the coil housing are fixed by cold solder welding to compress the heat pipe; The heat conduction material filled inside the heat conduction housing is selected as thermal conductive silicone rubber, which is a thermal conductive, room temperature curing silicone bonding and sealing adhesive; After the installation of the heat pipe and the coil housing is completed, two coil heat pipe assemblies are formed, and then they are installed with the phase change cold plate. During installation, it is required that the heat pipe be horizontal. The heat pipe is calibrated with a level, the levelness is adjusted with a heat pipe pressing plate, thermal conductive glue is applied to the installation contact surface between the heat pipe and the phase change cold plate, and the heat pipe is pressed by the pressing plate to ensure that the heat pipe is closely attached to the phase change cold plate.

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