A precision coaxial mounting method for a cold atom fountain clock vacuum assembly

Abstract

This invention relates to a method for precise coaxial installation of a vacuum component of a cold atom fountain clock, belonging to the field of cold atom clock technology. The method includes: using a three-dimensional magneto-optical trap cavity as an initial reference to position a selection cavity; preparing a non-magnetic metal rod, ensuring that the straightness and cylindricity of the non-magnetic metal rod meet preset threshold standards; using the selection cavity as a positioning reference for the excitation cavity, initially positioning the excitation cavity on the excitation cavity base; sequentially inserting the non-magnetic metal rod into the excitation cavity and the selection cavity from top to bottom, repeatedly pulling and retracting the non-magnetic metal rod for radial fine-tuning until the non-magnetic metal rod meets the coaxial positioning conditions; tightening the connector between the excitation cavity and the excitation cavity base, re-inserting the non-magnetic metal rod for verification, and completing the coaxial installation of the cold atom fountain clock vacuum component. This invention uses a physical entity reference instead of optical collimation, utilizing the feedback of the natural fall of the metal rod to achieve coaxial alignment, improving assembly accuracy and efficiency, and ensuring the long-term accuracy and stability of the cold atom fountain clock.

Description

Technical Field

[0001] This invention belongs to the field of cold atom clock technology, specifically relating to a method for precise coaxial installation of vacuum components in a cold atom fountain clock. Background Technology

[0002] The cold atom fountain clock is a crucial component of the International Atomic Time (IAT) generation and maintenance system, and cavity phase distribution shift is a key factor affecting its performance. This shift originates from the finite quality factor of the excitation cavity in the physical system. Energy losses at the cavity walls lead to uneven phase distribution of the microwave field within the cavity. These phase changes, coupled with atomic coupling, produce a first-order Doppler shift, known as the cavity phase distribution shift. To suppress this shift, the cold atom fountain clock employs a fountain-like operating mode, where atoms rise and fall through the same position within the same excitation cavity, thus canceling out their first-order Doppler effects.

[0003] The cold atom fountain clock vacuum system consists of a three-dimensional magneto-optical trap (3D-MOT), a selection cavity, a detection zone, and an excitation cavity, assembled along the direction of gravity. During system assembly, there is an assembly deviation of 0.1–0.2 mm between the axes of each cavity. After final assembly, the axis deviation between the excitation cavity, selection cavity, and magneto-optical trap may exceed 0.5 mm. Furthermore, the non-parallelism of the connecting surfaces of the cavities also leads to inconsistent axis angles. Since the diameter of the falling atom cluster is the same as the inner diameter of the excitation and selection cavities, the first-order Doppler effect cannot cancel each other out when the atom cluster flies through the vacuum system with assembly deviations. This causes the accuracy of the cold atom fountain clock to be affected by the frequency shift of the cavity phase distribution. Therefore, the design, manufacturing, and assembly of the fountain clock must ensure that the rising and falling paths of the cold atom cluster coincide, i.e., that the axes of the excitation cavity, selection cavity, and magneto-optical trap are aligned.

[0004] For ease of understanding, the three-dimensional magneto-optical trap, the state selection cavity, and the excitation cavity are collectively referred to as the vacuum assembly. The coaxiality between the state selection cavity and the excitation cavity is crucial for ensuring the atomic fallback ratio, the clock transition signal-to-noise ratio, and suppressing the frequency shift of the cavity phase distribution. Current methods achieve adjustment through laser collimation. First, a collimated laser beam is incident along the axial direction at the top of the cesium atomic fountain clock, passing sequentially through the excitation cavity and each cavity in the vacuum assembly. A liquid level tank is placed at the bottom of the device, using the naturally formed horizontal surface as a reflection reference surface. After the laser beam reaches the bottom and is reflected by the liquid surface, it returns along its original path. The degree of overlap between the returned beam and the emitted beam is detected. Subsequently, while keeping the laser reference axis unchanged, the lateral position of the excitation cavity is adjusted to achieve coaxial alignment with the lower vacuum assembly. However, this method requires first establishing a highly collimated laser reference axis, and then using this reference axis as a reference to calibrate the vacuum components. This makes it highly dependent on the accuracy and stability of the optical components. The final accuracy of the entire calibration system is limited by the pointing stability of the laser itself, the quality of the collimator, the flatness of the mirror, and the performance of optical components such as their installation stability. Even a tiny vibration or displacement of any component or its inherent optical aberration will introduce alignment errors during the calibration process. Secondly, the operation process is complex and lacks an efficient standardized procedure. Calibration personnel need to repeatedly manually iterate and adjust the position of the laser spot on multiple target surfaces by observing it. The entire process is time-consuming and not only leads to low calibration efficiency but also makes it difficult to ensure consistency and repeatability between different devices or different calibration results. Summary of the Invention

[0005] To address the aforementioned problems in the prior art, this invention provides a method for precise coaxial mounting of vacuum components in a cold atom fountain clock. The technical problem to be solved by this invention is achieved through the following technical solution: This invention provides a method for precise coaxial mounting of vacuum components in a cold atom fountain clock, comprising: S1: Using the three-dimensional magneto-optical trap cavity as the initial reference, position the state selection cavity so that the central axis of the state selection cavity coincides with the central axis of the three-dimensional magneto-optical trap cavity, and complete the construction of the lower vacuum assembly; S2: Prepare a non-magnetic metal rod, such that the straightness and cylindricity of the non-magnetic metal rod both meet a preset threshold standard; wherein, the preset threshold standard is: the non-magnetic metal rod falls naturally in the selection cavity and the excitation cavity under the action of gravity respectively; S3: Using the selected cavity as the positioning reference of the excitation cavity, retaining the radial translational degree of freedom of the excitation cavity, the excitation cavity is initially positioned on the excitation cavity base; S4: Insert the non-magnetic metal rod into the excitation cavity and the selection cavity sequentially from top to bottom, and make radial fine adjustments by repeatedly pulling the non-magnetic metal rod until the coaxial positioning condition is met; wherein, the coaxial positioning condition is: the non-magnetic metal rod falls naturally under the action of gravity and passes through the excitation cavity and the selection cavity sequentially. S5: Tighten the connector between the excitation chamber and the excitation chamber base, reinsert the non-magnetic metal rod for verification. If the coaxial positioning condition is still met, the coaxial installation of the cold atom fountain clock vacuum assembly is complete.

[0006] In one embodiment of the present invention, step S1, using the three-dimensional magneto-optical trap cavity as an initial reference, involves locating the state selection cavity, including: Using the three-dimensional magneto-optical trap cavity as the initial reference, the selected cavity is positioned by clamping it from the side using three clips evenly distributed at 120°. The inner contour shape of each clip matches the plane of the outer contour of the three-dimensional magneto-optical trap cavity.

[0007] In one embodiment of the present invention, the non-magnetic metal rod is made of TC4 titanium alloy, and the initial diameter of the non-magnetic metal rod is smaller than the inner diameter of the selection cavity and the excitation cavity.

[0008] In one embodiment of the present invention, step S2 involves preparing a non-magnetic metal rod, ensuring that the straightness and cylindricity of the non-magnetic metal rod both meet a preset threshold standard, including: The non-magnetic metal rod is polished and then subjected to stress-relieving heat treatment until the straightness and cylindricity of the non-magnetic metal rod meet the preset threshold standards. The straightness and cylindricity error range of the outer diameter of the non-magnetic metal rod after polishing is 0~0.02 mm over its entire length.

[0009] In one embodiment of the present invention, the radial translational degree of freedom of the excitation cavity is achieved by the preload of the connecting bolts between the excitation cavity and the excitation cavity base.

[0010] In one embodiment of the present invention, step S4, radial fine-tuning by repeatedly pulling the non-magnetic metal rod, includes: When the non-magnetic metal rod is obstructed from descending, it is used as a lever to apply a lateral force to the excitation cavity by repeatedly pulling and rotating it, thereby driving the excitation cavity to produce radial translation until the non-magnetic metal rod meets the coaxial positioning condition.

[0011] In one embodiment of the present invention, the coaxial positioning condition further includes: the non-magnetic metal rod falls naturally under the action of gravity, and when the non-magnetic metal rod is rotated, the frictional torque between its surface and the inner walls of the excitation cavity and the selection cavity is uniformly distributed.

[0012] In one embodiment of the present invention, step S5, fastening the connector between the excitation cavity and the excitation cavity base includes: vertically lifting the upper vacuum cavity assembly containing the excitation cavity while the non-magnetic metal rod is in the through state, exposing the fastening space below the excitation cavity base; Within the fastening space, the torque is increased in a diagonal sequence to sequentially tighten the connecting bolts between the excitation chamber and the excitation chamber base.

[0013] In one embodiment of the present invention, in step S5, after re-inserting the non-magnetic metal rod for verification, if the coaxial positioning condition is not met, the connecting piece between the excitation cavity and the excitation cavity base is loosened, and S4 is repeated until the coaxial positioning condition is met.

[0014] In one embodiment of the present invention, step S5 is followed by: S6: Calculate the residual eccentricity error of the excitation cavity after adjustment. Its expression is: ; in, The radial gap on one side between the non-magnetic metal rod and the inner wall of the selected cavity; The axial distance between the lower cutoff waveguide of the excitation cavity and the upper cutoff waveguide of the selected cavity; The axial length of the selected cavity.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention discloses a precision coaxial installation method for the vacuum assembly of a cold atom fountain clock. It uses a three-dimensional magneto-optical trap cavity as the initial reference for positioning the selection cavity. A non-magnetic metal rod is then used to allow it to fall naturally under gravity through the selection cavity and the excitation cavity, providing a physical reference for subsequent adjustments. During adjustment, radial fine-tuning is performed by repeatedly pulling and rotating the non-magnetic metal rod. The feedback from the natural fall of the metal rod serves as the coaxial positioning condition, thus replacing optical collimation with a physical reference. This eliminates dependence on optical components and avoids errors introduced by environmental factors. Furthermore, the objective and repeatable judgment criterion of natural fall enables a standardized coaxial installation process, significantly improving assembly efficiency and reproducibility. Additionally, the residual eccentricity error can be obtained based on the dimensional relationship between the non-magnetic metal rod and the cavity, which can be used to evaluate the cavity phase distribution frequency shift of the cold atom fountain clock, providing a guarantee for the engineering application of cold atom clocks.

[0016] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described in detail below with reference to the accompanying drawings. Attached Figure Description

[0017] Figure 1 This is a flowchart of a method for precise coaxial installation of a vacuum component of a cold atom fountain clock, provided in an embodiment of the present invention. Figure 2 This is a schematic diagram of the vacuum assembly of the cold atom fountain clock provided in an embodiment of the present invention; Figure 3 This is a schematic diagram of the operation of the non-magnetic metal rod provided in an embodiment of the present invention; Figure 4 This is a schematic diagram of the residual eccentricity error of the vacuum component of the cold atom fountain clock provided in an embodiment of the present invention.

[0018] Reference numerals: 100-Clamping piece; 200-Three-dimensional magneto-optical trap cavity; 300-Selective cavity; 301-Selective cavity lower cutoff waveguide; 302-Selective cavity upper cutoff waveguide; 400-Non-magnetic metal rod; 500-Excitation cavity base; 600-Excitation cavity; 601-Excitation cavity lower cutoff waveguide; 602-Excitation cavity upper cutoff waveguide; 700-Lower vacuum assembly; Detailed Implementation To further illustrate the technical means and effects adopted by the present invention to achieve the intended purpose, the following describes in detail, with reference to the accompanying drawings and specific embodiments, a method for precise coaxial installation of vacuum components of a cold atom fountain clock according to the present invention.

[0019] The foregoing and other technical contents, features, and effects of the present invention will be clearly presented in the following detailed description of specific embodiments in conjunction with the accompanying drawings. Through the description of the specific embodiments, a more in-depth and concrete understanding can be gained of the technical means and effects adopted by the present invention to achieve its intended purpose. However, the accompanying drawings are for reference and illustration only and are not intended to limit the technical solutions of the present invention.

[0020] Example 1 Existing methods for coaxial installation of vacuum components involve numerous optical devices, are susceptible to environmental interference, are time-consuming, cannot achieve standardized operation, and cannot accurately quantify and assess errors. Therefore, this invention provides a method for precise coaxial installation of vacuum components in a cold atom fountain clock, such as… Figures 1 to 4 As shown, Figure 1 This is a flowchart of a method for precise coaxial installation of a vacuum component of a cold atom fountain clock, provided in an embodiment of the present invention. Figure 2This is a schematic diagram of the vacuum assembly of the cold atom fountain clock provided in an embodiment of the present invention; Figure 3 This is a schematic diagram of the operation of the non-magnetic metal rod provided in an embodiment of the present invention; Figure 4 This is a schematic diagram of the residual eccentricity error of the vacuum component of the cold atom fountain clock provided in an embodiment of the present invention.

[0021] In this embodiment, the present invention provides a method for precise coaxial mounting of vacuum components of a cold atom fountain clock, comprising: S1: Using the three-dimensional magneto-optical trap cavity 200 as the initial reference, position the selection cavity 300 so that the central axis of the selection cavity 300 coincides with the central axis of the three-dimensional magneto-optical trap cavity 200, and complete the construction of the lower vacuum assembly 700.

[0022] In one embodiment of the present invention, step S1, using the three-dimensional magneto-optical trap cavity 200 as an initial reference, positions the selection cavity 300, including: using the three-dimensional magneto-optical trap cavity 200 as an initial reference, and using three clamping pieces 100 evenly distributed at 120° to clamp and position the selection cavity 300 from the side; wherein, the inner contour shape of each clamping piece 100 matches the plane of the outer contour of the three-dimensional magneto-optical trap cavity 200, specifically, the inner contour of each clamping piece 100 has a reference surface that matches the positioning surface of the three-dimensional magneto-optical trap cavity 200, and the outer contour of the clamping piece 100 has a preset geometric offset relative to the reference surface, so as to ensure that the central axis enclosed by the three clamping pieces 100 coincides with the central axis of the selection cavity 300.

[0023] Specifically, such as Figure 2 As shown, using the three-dimensional magneto-optical trap cavity 200 as the initial reference, the three-dimensional magneto-optical trap cavity 200 and the selection cavity 300 are installed sequentially from bottom to top. To achieve coaxiality between the three-dimensional magneto-optical trap cavity 200 and the selection cavity 300, three pre-machined clamping plates 100 are used. After being fixed on the top three sides of the three-dimensional magneto-optical trap cavity 200, the selection cavity 300 is clamped. The three clamping plates 100 are evenly distributed at 120°, and the inner contour shape of each clamping plate 100 matches the positioning plane of the outer contour of the three-dimensional magneto-optical trap cavity 200. By applying a balanced clamping force from three sides, the central axis of the three-dimensional magneto-optical trap cavity 200 is made to coincide with the virtual axis defined by the geometric center of the clamping plate 100, thereby transforming the center of the non-cylindrical cavity into a mechanically alignable reference. After positioning the center, the selection cavity 300 is fixed to ensure the collinearity of its axes. Understandably, since the inner diameter of the other connecting components between the selection cavity 300 and the upper vacuum cavity is much larger than the inner diameter of the cutoff waveguide of the selection cavity 300 and the excitation cavity 600, their impact on the coaxiality of the entire system is negligible. Finally, the other components are installed sequentially above the selection cavity 300 to complete the construction of the lower vacuum assembly 700.

[0024] S2: Prepare a non-magnetic metal rod 400, such that the straightness and cylindricity of the non-magnetic metal rod 400 both meet the preset threshold standards; wherein, the preset threshold standards are: the non-magnetic metal rod 400 falls naturally in the selection cavity 300 and the excitation cavity 600 under the action of gravity.

[0025] During the fabrication process, the non-magnetic metal rod 400 is polished, and then subjected to stress-relieving heat treatment until the straightness and cylindricity of the non-magnetic metal rod 400 meet the preset threshold standards. Specifically, the inner diameters of the lower cutoff waveguide 301 and upper cutoff waveguide 302 of the selection cavity 300, and the lower cutoff waveguide 601 and upper cutoff waveguide 602 of the excitation cavity 600 are all equal. The initial diameter of the non-magnetic metal rod 400 is smaller than the inner diameters of the selection cavity 300 and the excitation cavity 600. After processing, the non-magnetic metal rod 400 is initially attempted to pass through the selection cavity 300 and the excitation cavity 600, respectively, requiring it to fit tightly against the inner walls of the selection cavity 300 and the excitation cavity 600 and pass smoothly under controllable friction. The non-magnetic metal rod 400, which passed the initial test, was polished with ultra-high precision fine sandpaper on its outer diameter. Before installing the entire lower vacuum assembly 700, it was repeatedly passed through the selection cavity 300 and the excitation cavity 600 individually to ensure a tight fit under controllable friction. Then, rotation was added during the passage, ensuring that the rotation was also smooth and without jamming. Subsequently, the straightness and cylindricity of the non-magnetic metal rod 400 were measured at multiple points along its entire length using high-precision vernier calipers. This ensured that the straightness and cylindricity error range of the outer diameter of the non-magnetic metal rod 400 along its entire length was 0~0.02 mm. This satisfies the clearance fit requirements with the upper and lower cutoff waveguides of the selection cavity 300 and the excitation cavity 600, ensuring that the non-magnetic metal rod 400 can fall naturally within the selection cavity 300 and the excitation cavity 600 under gravity, and can also achieve minute displacement drive of the excitation cavity 600 through rigid transmission when obstructed.

[0026] Preferably, the non-magnetic metal rod 400 is made of TC4 titanium alloy and has undergone stress-relieving heat treatment. TC4 titanium alloy is non-magnetic, has high specific strength, good elastic modulus and dimensional stability. It is not easy to produce plastic deformation during repeated drawing and pulling, and can maintain straightness and cylindricity, while avoiding interference with the magnetic field environment of the atomic fountain clock.

[0027] Understandably, controllable friction refers to the process of creating a gap fit between the non-magnetic metal rod 400 and the inner wall of the cavity, allowing the non-magnetic metal rod 400 to fall naturally under gravity. At the same time, when the downward movement is obstructed, the lateral force applied by the operator can be effectively transmitted to the excitation cavity through the contact point between the non-magnetic metal rod 400 and the inner wall of the cavity. The magnitude of this friction is within a controllable range, neither too large to cause the non-magnetic metal rod 400 to jam nor too small to prevent the transmission of adjustment force.

[0028] S3: Using the selected cavity 300 as the positioning reference for the excitation cavity 600, the radial translational degree of freedom of the excitation cavity 600 is retained, and the excitation cavity 600 is initially positioned on the excitation cavity base 500.

[0029] The radial translational freedom of the excitation cavity 600 is achieved through the preload of the connecting bolts between the excitation cavity 600 and the excitation cavity base 500. Specifically, using the selection cavity 300 as the positioning reference for the excitation cavity 600, the excitation cavity 600 is initially placed on the excitation cavity base 500 within the vacuum cavity. The connecting bolts between the excitation cavity 600 and the excitation cavity base 500 are preloaded but not fully locked. The preload of the connecting bolts allows the excitation cavity 600 to retain a controllable minute radial translational freedom, while preventing the excitation cavity 600 from sliding under gravity, ensuring a smooth and controllable adjustment process. Finally, the entire upper vacuum cavity assembly, including the excitation cavity 600, is initially docked with the lower vacuum assembly 700.

[0030] S4: Insert the non-magnetic metal rod 400 into the excitation cavity 600 and the selection cavity 300 sequentially from top to bottom, and make radial fine adjustments by repeatedly pulling the non-magnetic metal rod 400 until the coaxial positioning condition is met. The coaxial positioning conditions are as follows: the non-magnetic metal rod 400 falls naturally under gravity, passing through the excitation cavity 600 and the selection cavity 300 in sequence; at the same time, the non-magnetic metal rod 400 falls naturally under gravity. When the non-magnetic metal rod 400 is rotated, the friction torque between its surface and the inner walls of the excitation cavity 600 and the selection cavity 300 is evenly distributed, that is, there is no obvious jamming. This indicates that the contact state between the non-magnetic metal rod 400 and the inner wall of the cavity is consistent in the entire circumferential direction, and the central axis of the non-magnetic metal rod 400 coincides with the central axis of the cavity, thereby avoiding misjudgment caused by local contact.

[0031] In one embodiment of the present invention, step S4 involves radial fine-tuning by repeatedly pulling and retracting the non-magnetic metal rod 400, including: when the non-magnetic metal rod 400 is obstructed from descending, using the non-magnetic metal rod 400 as a lever, applying a lateral force to the excitation cavity 600 by repeatedly pulling and rotating, driving the excitation cavity 600 to produce radial translation until the non-magnetic metal rod 400 meets the coaxial positioning condition.

[0032] Specifically, such as Figure 2 and Figure 3As shown, the operator vertically and slowly inserts the non-magnetic metal rod 400 into the excitation cavity 600 through the cutoff waveguide 602 port, allowing it to pass through the excitation cavity 600 and other vacuum components before finally entering the selection cavity 300. At this point, the non-magnetic metal rod 400 becomes a solid connecting rod between the excitation cavity 600 and the selection cavity 300. The dashed line represents the central axis of the entire system, with the selection cavity 300 as the reference. During this process, when the non-magnetic metal rod 400 encounters resistance in its downward movement, it is used as a lever. By repeatedly pulling and rotating the non-magnetic metal rod 400, a lateral force is applied to the excitation cavity 600, driving it to radially translate. After one fine-tuning, the non-magnetic metal rod 400 is completely withdrawn to release stress, and then reinserted for verification. This cycle of insertion, resistance-related fine-tuning, withdrawal and release, and reinsertion verification is repeated until the non-magnetic metal rod 400 meets the coaxial positioning condition.

[0033] It is worth noting that the non-magnetic metal rod 400 serves as both a coaxiality detection fixture and a displacement transfer medium. When the non-magnetic metal rod 400 extends vertically into the excitation cavity from the cutoff waveguide 602 and falls naturally under gravity, if there is a coaxial deviation between the excitation cavity 600 and the selection cavity 300, the non-magnetic metal rod 400 will contact the inner wall of the port of the cutoff waveguide 302 in the selection cavity. Furthermore, because the non-magnetic metal rod 400 and the inner wall of the selection cavity 300 are in a clearance fit, the non-magnetic metal rod 400 will not be in contact with the inner wall of the excitation cavity 300. When the excitation chamber 600 and the selection chamber 300 become stuck, the operator only needs to apply a slight rotation or pulling motion to the upper end of the non-magnetic metal rod 400. Rotation causes circumferential displacement at the contact point between the non-magnetic metal rod 400 and the chamber, while pulling causes axial slight movement, thus transmitting lateral force to the excitation chamber 600. Finally, the rigidity of the non-magnetic metal rod 400 pushes the excitation chamber 600 to produce a slight radial translation on the excitation chamber base 500. Throughout the process, because the non-magnetic metal rod 400 maintains a clearance fit with the inner wall of the chamber and the contact force is small, and because the surface of the non-magnetic metal rod 400 is treated with ultra-precision grinding, it ensures that no wear is caused to the inner wall of the chamber while transmitting displacement.

[0034] S5: Tighten the connector between the excitation chamber 600 and the excitation chamber base 500, and reinsert the non-magnetic metal rod 400 for verification. If the coaxial positioning condition is still met, the coaxial installation of the cold atom fountain clock vacuum assembly is completed. If the coaxial positioning condition is not met, loosen the connector between the excitation chamber 600 and the excitation chamber base 500, and repeat S4 until the coaxial positioning condition is met.

[0035] In one embodiment of the present invention, step S5, fastening the connector between the excitation cavity 600 and the excitation cavity base 500, includes: with the non-magnetic metal rod 400 in a through state, vertically lifting the upper vacuum cavity assembly containing the excitation cavity 600 to expose the fastening space below the excitation cavity base 500; and sequentially tightening the connecting bolts between the excitation cavity 600 and the excitation cavity base 500 in the fastening space with the torque increasing in a diagonal cross order.

[0036] Specifically, after achieving the coaxial positioning condition, since the final fastening point of the excitation cavity 600 is located below the excitation cavity base 500, a specialized hoisting guide fixture is used to ensure verticality while the non-magnetic metal rod 400 is in the through-hole state. Then, the upper vacuum cavity assembly containing the excitation cavity 600 is vertically hoisted to expose the fastening space below the excitation cavity base 500. Within this fastening space, the torque is increased diagonally, and the connecting bolts between the excitation cavity 600 and the excitation cavity base 500 are tightened sequentially to ensure uniform force on the excitation cavity base 500. Afterward, the upper vacuum cavity assembly is hoisted back into position and re-connected and sealed with the lower vacuum assembly 700. Finally, a final verification is performed: the non-magnetic metal rod 400 is reinserted to perform a full-range sliding test. If the coaxial positioning condition of the non-magnetic metal rod 400 naturally falling under gravity and sequentially passing through the excitation cavity 600 and the selection cavity 300 is still met, it indicates that the coaxiality has been reliably established. If the coaxial positioning condition is not met, loosen the connection between the excitation chamber 600 and the excitation chamber base 500, and repeat step S4 until the coaxial positioning condition is met.

[0037] Understandably, hoisting guide fixtures are conventional assembly auxiliary tools in this field, and their specific structure and usage methods are well known to those skilled in the art, so they will not be described in detail here.

[0038] S6: Calculate the residual eccentricity error of the excitation cavity 600 after adjustment. Its expression is: ; in, The radial gap on one side between the non-magnetic metal rod 400 and the inner wall of the selection cavity 300; The axial distance between the lower cutoff waveguide 601 of the excitation cavity and the upper cutoff waveguide 302 of the selected cavity; The axial length of the selected cavity 300.

[0039] After adjustment, the residual eccentricity error of the excitation cavity 600 after adjustment can be calculated based on the dimensional relationship between the excitation cavity 600, the selected cavity 300 and the non-magnetic metal rod 400 obtained during the adjustment process. This is used to quantitatively evaluate the cavity phase distribution frequency shift of the cold atom fountain clock, thereby providing accurate input parameters for subsequent frequency offset correction. By incorporating the input parameters into the system error model, the frequency accuracy and long-term stability of the atomic clock can be further improved.

[0040] Specifically, such as Figures 2 to 4 As shown, the diameter of the non-magnetic metal rod 400 and the inner diameters of the excitation cavity 600 and the selection cavity 300 are first obtained through multi-point measurements, and the radial gap on one side between the non-magnetic metal rod 400 and the inner wall of the selection cavity 300 is obtained. Then, by constructing a geometric relationship (similar triangle) between the distance between the excitation cavity 600 and the selection cavity 300 and the deviation of the inner diameter of the non-magnetic metal rod 400 and the selection cavity 300, the residual eccentricity error can be calculated. .

[0041] The present invention discloses a precision coaxial installation method for the vacuum assembly of a cold atom fountain clock. Using a three-dimensional magneto-optical trap cavity 200 as the initial reference, the selection cavity 300 is positioned. A non-magnetic metal rod 400 is then allowed to fall naturally under gravity through the selection cavity 300 and the excitation cavity 600, providing a physical reference for subsequent adjustments. During adjustment, radial fine-tuning is performed by repeatedly pulling and rotating the non-magnetic metal rod 400. The feedback from the natural fall of the non-magnetic metal rod 400 serves as the coaxial positioning condition, thus replacing optical collimation with a physical reference. This eliminates dependence on optical components and avoids errors introduced by environmental factors. Furthermore, the objective and repeatable judgment criterion of natural fall enables a standardized coaxial installation process, significantly improving assembly efficiency and reproducibility. Additionally, the residual eccentricity error can be obtained based on the dimensional relationship between the non-magnetic metal rod 400 and the cavity, which can be used to evaluate the cavity phase distribution frequency shift of the cold atom fountain clock, providing assurance for the engineering application of cold atom clocks.

[0042] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations are intended to cover non-exclusive inclusion, such that an article or device comprising a list of elements includes not only those elements but also other elements not expressly listed. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the article or device comprising said element. Terms such as "connected" or "linked" are not limited to physical or mechanical connections but can include electrical connections, whether direct or indirect. The orientations or positional relationships indicated by terms such as "upper," "lower," "left," and "right" are based on the orientations or positional relationships shown in the accompanying drawings and are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as limiting the invention.

[0043] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A method for precision coaxial mounting of a cold atom fountain clock vacuum assembly, characterized in that, include: S1: Using the three-dimensional magneto-optical trap cavity as the initial reference, position the state selection cavity so that the central axis of the state selection cavity coincides with the central axis of the three-dimensional magneto-optical trap cavity, thus completing the construction of the lower vacuum assembly; S2: Prepare a non-magnetic metal rod, such that the straightness and cylindricity of the non-magnetic metal rod both meet a preset threshold standard; wherein, the preset threshold standard is: the non-magnetic metal rod falls naturally in the selection cavity and the excitation cavity under the action of gravity respectively; S3: Using the selected cavity as the positioning reference of the excitation cavity, retaining the radial translational degree of freedom of the excitation cavity, the excitation cavity is initially positioned on the excitation cavity base; S4: Insert the non-magnetic metal rod into the excitation cavity and the selection cavity sequentially from top to bottom, and make radial fine adjustments by repeatedly pulling the non-magnetic metal rod until the coaxial positioning condition is met; wherein, the coaxial positioning condition is: the non-magnetic metal rod falls naturally under the action of gravity and passes through the excitation cavity and the selection cavity sequentially. S5: Tighten the connector between the excitation chamber and the excitation chamber base, reinsert the non-magnetic metal rod for verification. If the coaxial positioning condition is still met, the coaxial installation of the cold atom fountain clock vacuum assembly is complete.

2. The method for precise coaxial installation of the vacuum components of a cold atom fountain clock according to claim 1, characterized in that, In S1, using the three-dimensional magneto-optical trap cavity as the initial reference, the selected state cavity is located, including: Using the three-dimensional magneto-optical trap cavity as the initial reference, the selected cavity is positioned by clamping it from the side using three clips evenly distributed at 120°. The inner contour shape of each clip matches the plane of the outer contour of the three-dimensional magneto-optical trap cavity.

3. The method for precise coaxial installation of the vacuum components of a cold atom fountain clock according to claim 1, characterized in that, The non-magnetic metal rod is made of TC4 titanium alloy, and the initial diameter of the non-magnetic metal rod is smaller than the inner diameter of the selection cavity and the excitation cavity.

4. The method for precise coaxial installation of the vacuum components of a cold atom fountain clock according to claim 3, characterized in that, In S2, a non-magnetic metal rod is prepared, ensuring that the straightness and cylindricity of the non-magnetic metal rod both meet preset threshold standards, including: The non-magnetic metal rod is polished and then subjected to stress-relieving heat treatment until the straightness and cylindricity of the non-magnetic metal rod meet the preset threshold standards. The straightness and cylindricity error range of the outer diameter of the non-magnetic metal rod after polishing is 0~0.02 mm over its entire length.

5. The method for precise coaxial installation of the vacuum components of a cold atom fountain clock according to claim 1, characterized in that, The radial translational freedom of the excitation cavity is achieved by the preload of the connecting bolts between the excitation cavity and the excitation cavity base.

6. The method for precise coaxial installation of the vacuum components of a cold atom fountain clock according to claim 5, characterized in that, In S4, radial fine-tuning is performed by repeatedly pulling and stretching the non-magnetic metal rod, including: When the non-magnetic metal rod is obstructed from descending, it is used as a lever to apply a lateral force to the excitation cavity by repeatedly pulling and rotating it, thereby driving the excitation cavity to produce radial translation until the non-magnetic metal rod meets the coaxial positioning condition.

7. The method for precise coaxial installation of the vacuum components of a cold atom fountain clock according to claim 6, characterized in that, The coaxial positioning conditions also include: the non-magnetic metal rod falls naturally under the action of gravity, and when the non-magnetic metal rod is rotated, the frictional torque between its surface and the inner walls of the excitation cavity and the selection cavity is evenly distributed.

8. The method for precise coaxial installation of vacuum components of a cold atom fountain clock according to claim 1, characterized in that, In S5, fastening the connector between the excitation cavity and the excitation cavity base includes: vertically lifting the upper vacuum cavity assembly containing the excitation cavity while the non-magnetic metal rod is in the through state, exposing the fastening space below the excitation cavity base; Within the fastening space, the torque is increased in a diagonal sequence to sequentially tighten the connecting bolts between the excitation chamber and the excitation chamber base.

9. The method for precise coaxial installation of vacuum components of a cold atom fountain clock according to claim 1, characterized in that, In S5, after re-inserting the non-magnetic metal rod for verification, if the coaxial positioning condition is not met, the connection between the excitation cavity and the excitation cavity base is loosened, and S4 is repeated until the coaxial positioning condition is met.

10. The method for precise coaxial installation of the vacuum components of a cold atom fountain clock according to claim 1, characterized in that, S5 also includes: S6: Calculate the residual eccentricity error of the excitation cavity after adjustment. Its expression is: ； in, The radial gap on one side between the non-magnetic metal rod and the inner wall of the selected cavity; The axial distance between the lower cutoff waveguide of the excitation cavity and the upper cutoff waveguide of the selected cavity; The axial length of the selected cavity.

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