Method for producing a composite coating on the inner wall of a vacuum tube and vacuum tube

Abstract

The present application relates to the technical field of particle accelerators, in particular to a method for preparing a composite coating on the inner wall of a vacuum pipe and a vacuum pipe. The preparation method comprises: roughening the inner wall of the vacuum pipe; coaxially installing the treated vacuum pipe in a solenoid of a magnetron sputtering coating device; using a magnetron sputtering coating process to coat an Au film on the inner wall of the vacuum pipe; and using a magnetron sputtering coating process to coat a TiZrV film on the side of the Au film away from the vacuum pipe. In the present application, the Au / TiZrV double-layer film is coated on the inner wall of the vacuum pipe, so that a double-layer structure of a dense barrier layer and an active getter layer is formed on the surface of the vacuum pipe, which can effectively block the diffusion of the gas of the pipe wall material into the vacuum system by using the dense characteristics of the Au film, and can also make the TiZrV film fully play the gettering efficiency, thereby reducing the beam bombardment desorption rate of the vacuum pipe.

Description

Technical Field

[0001] This invention relates to the field of particle accelerator technology, and in particular to a method for preparing a composite coating on the inner wall of a vacuum pipe and the vacuum pipe itself. Background Technology

[0002] The performance of a particle accelerator is highly dependent on the quality of its vacuum system. Ultra-high vacuum (typically requiring 10⁻⁵) is crucial. -6 Pa to 10 -9 (Pa level) and extremely high vacuum (typically required to be less than 10). -9 The ultimate vacuum (on the order of Pa) is crucial for reducing collisions between the beam and residual gas molecules, ensuring beam lifetime and stability. To improve the quality of the vacuum system in a particle accelerator, efforts must be made in the following two aspects: 1. Obtaining and maintaining a better ultimate vacuum; 2. Reducing the rate at which the material inside the tube releases gas under beam bombardment (especially high-energy proton or heavy ion beams) (i.e., beam bombardment desorption rate).

[0003] Traditional methods involve using high baking temperatures (e.g., 200-300℃) to remove water vapor and other gases adsorbed on the inner walls of stainless steel vacuum pipes, relying on external sputtering ion pumps or titanium sublimation pumps to maintain the vacuum level. However, the walls of stainless steel vacuum pipes continue to release gases such as hydrogen after baking, and the high beam bombardment desorption rate of stainless steel vacuum pipes makes it difficult for the vacuum system to maintain ultra-high and very high vacuum levels.

[0004] Currently, vacuum pipelines are typically coated with non-evaporable getter (NEG) coatings to enhance ultimate vacuum and reduce desorption rates. In particular, TiZrV ternary getter films, after being baked and activated at 180-300℃, can provide distributed pumping speeds for reactive gases (such as H2, CO, CO2, N2, etc.) at room temperature.

[0005] However, the coating technology for TiZrV ternary getter films still faces bottlenecks: the TiZrV ternary getter film itself has pores, which cannot completely block the diffusion of hydrogen from the interior of the stainless steel substrate (or commonly used substrates such as copper and aluminum). Since hydrogen continuously diffuses from the substrate into the vacuum chamber through the TiZrV ternary getter film, vacuum pipes equipped only with the TiZrV ternary getter film cannot maintain a high vacuum level in the vacuum system for a long period of time. Summary of the Invention

[0006] This invention aims to solve the technical problems existing in related technologies. To this end, this invention proposes a method for preparing a composite coating on the inner wall of a vacuum pipe and a vacuum pipe itself, thereby improving the physical properties of the vacuum pipe and reducing the beam bombardment desorption rate.

[0007] In a first aspect, the present invention provides a method for preparing a composite coating on the inner wall of a vacuum pipe, comprising:

[0008] The inner wall of the vacuum pipe is roughened.

[0009] The processed vacuum pipe is coaxially installed inside the solenoid of the magnetron sputtering coating device.

[0010] Au film was deposited on the inner wall of a vacuum pipe using magnetron sputtering coating technology;

[0011] A TiZrV film was deposited on the side of the Au film away from the vacuum pipe using a magnetron sputtering coating process.

[0012] According to the present invention, a method for preparing a composite coating on the inner wall of a vacuum pipe includes the following specific steps for depositing an Au film on the inner wall of the vacuum pipe using a magnetron sputtering deposition process:

[0013] Install the Au target at the center axis of the vacuum pipeline;

[0014] The vacuum pipeline is evacuated, and then inert gas is introduced into the vacuum pipeline until the gas pressure inside the vacuum pipeline reaches the preset sputtering pressure.

[0015] The solenoid is activated to generate an axial magnetic field. A DC negative bias voltage is applied to the Au target, and the vacuum pipe is grounded to create a radial electric field between the Au target and the vacuum pipe.

[0016] According to the present invention, a method for preparing a composite coating on the inner wall of a vacuum pipe includes the following specific steps for depositing a TiZrV film on the side of the Au film facing away from the vacuum pipe using a magnetron sputtering deposition process:

[0017] S31. Stop evacuating the vacuum pipe, then fill the vacuum pipe with nitrogen to prevent Au film oxidation, and replace the Au target with a TiZrV composite target.

[0018] S32. Evacuate the vacuum pipeline and then introduce inert gas into the vacuum pipeline until the gas pressure in the vacuum pipeline reaches the preset sputtering pressure.

[0019] S33. Start the solenoid to generate an axial magnetic field, apply a DC negative bias voltage to the TiZrV composite target, and ground the vacuum pipe to form a radial electric field between the TiZrV composite target and the vacuum pipe.

[0020] According to the present invention, a method for preparing a composite coating on the inner wall of a vacuum pipe, wherein the roughening treatment of the inner wall of the vacuum pipe includes:

[0021] The inner wall of the vacuum pipe is roughened by at least one of the following methods: sandblasting, chemical etching, and mechanical threading.

[0022] According to the present invention, a method for preparing a composite coating on the inner wall of a vacuum pipe is provided, wherein the thickness of the Au film is between 100 nm and 500 nm.

[0023] According to the present invention, a method for preparing a composite coating on the inner wall of a vacuum pipe is provided, wherein the thickness of the TiZrV film is between 0.5 μm and 4.0 μm.

[0024] According to the present invention, a method for preparing a composite coating on the inner wall of a vacuum pipe is provided, wherein the strength of the axial magnetic field generated by the solenoid is between 200 Gauss and 400 Gauss, and the voltage value of the DC negative bias applied to the Au target or TiZrV composite target is between -250V and -600V.

[0025] According to the present invention, a method for preparing a composite coating on the inner wall of a vacuum pipe is provided, wherein the pressure of the inert gas in the vacuum pipe is between 0.1 Pa and 1 Pa.

[0026] According to the present invention, a method for preparing a composite coating on the inner wall of a vacuum pipe is provided, wherein the TiZrV composite target is made by winding Ti, Zr, and V elemental wires in an atomic ratio of 1:1:1.

[0027] Secondly, the present invention also provides a vacuum pipe, the inner wall of which is provided with a composite coating, the composite coating being prepared by any one of the methods described above for preparing a composite coating on the inner wall of a vacuum pipe.

[0028] The above-described one or more technical solutions of this invention have at least one of the following technical effects:

[0029] In this invention, by depositing an Au / TiZrV double-layer film on the inner wall of the vacuum pipe, a double-layer structure of a dense barrier layer and an active gas-getting layer is formed on the surface of the vacuum pipe. This can effectively block the diffusion of gas from the pipe wall material into the vacuum system by utilizing the dense properties of the Au film, and also allow the TiZrV film to fully exert its gas-getting efficiency, thereby reducing the beam bombardment desorption rate of the vacuum pipe.

[0030] In addition to the technical problems solved by the present invention, the technical features of the technical solutions constituted by the present invention, and the advantages brought about by the technical features of these technical solutions as described above, other technical features of the present invention and the advantages brought about by these technical features will be further explained in conjunction with the accompanying drawings, or will be learned through the practice of the present invention. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention or related technologies, the drawings used in the description of the embodiments or related technologies will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 This is a flowchart of a method for preparing a composite coating on the inner wall of a vacuum pipe, provided in an embodiment of the present invention.

[0033] Figure 2 This is a schematic diagram of the composite coating preparation apparatus provided in an embodiment of the present invention.

[0034] Figure 3 This is a schematic diagram of a composite coating applied to a vacuum pipe according to an embodiment of the present invention.

[0035] Figure label:

[0036] 1. Vacuum piping; 2. Solenoid; 3. Target material; 4. Sealing flange; 5. Auxiliary vacuum chamber; 6. Measuring element; 7. Inlet valve; 8. Pumping unit. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0038] In an embodiment of the present invention, a method for preparing a composite coating on the inner wall of a vacuum pipe is described.

[0039] like Figure 3 As shown, the composite coating structure on the inner wall of the vacuum pipe is as follows: the bottom layer is an Au film, and the top layer is a TiZrV film. By depositing an Au / TiZrV double-layer film on the inner wall of the vacuum pipe, a dual-layer structure of a dense barrier layer and an active gas-getter layer is formed on the surface of the vacuum pipe. This effectively blocks the diffusion of gas from the pipe wall material into the vacuum system by utilizing the dense properties of the Au film, while allowing the TiZrV film to fully exert its gas-getter efficiency, thereby reducing the beam bombardment desorption rate of the vacuum pipe.

[0040] like Figure 2As shown, the magnetron sputtering coating apparatus for preparing composite coatings includes a solenoid 2, a target 3, a sealing flange 4, an auxiliary vacuum chamber 5, a measuring element 6, an inlet valve 7, and a pumping unit 8. The central axis of the vacuum pipe 1 coincides with the central axis of the solenoid 2 to ensure that the central axis of the vacuum pipe 1 is parallel to the axial magnetic field generated by the solenoid 2.

[0041] like Figure 1 As shown, the preparation method of the composite coating specifically includes the following steps:

[0042] S1. Pre-treatment of the inner wall of the vacuum pipe. Specifically, the pre-treatment includes roughening the inner wall of the vacuum pipe. This is to remove inert barrier layers such as physical adsorbates, chemical adsorbates, and oxide layers from the surface of the inner wall of the vacuum pipe, and to create active sites on the surface of the inner wall of the vacuum pipe.

[0043] Roughening treatment can be achieved through one or more combinations of sandblasting, chemical etching, or mechanical threading. For example, sandblasting can be performed on the inner wall of a 316L stainless steel pipe approximately 3 meters long and 100 millimeters in inner diameter. The abrasive used in sandblasting is alumina, which can achieve a surface roughness of Ra 2.5 μm on the inner wall of the vacuum pipe.

[0044] After sandblasting, the vacuum pipe undergoes ultrasonic cleaning and high-temperature drying to remove surface adsorbates and oxide layers. Preferably, the roughness of the inner wall of the vacuum pipe is between Ra 3.2 μm and Ra 10.0 μm.

[0045] By roughening the inner wall of the pipe, the effective area for film deposition is increased, improving the adhesion strength between the film and the pipe wall surface and preventing the film from peeling off during use. More importantly, roughening the pipe wall surface also increases the specific surface area of ​​the film, exposing more active adsorption sites, thereby significantly improving the stability and durability of the film and preventing the composite coating from peeling off due to stress or thermal shock during use.

[0046] S2. The pre-treated vacuum pipe is coaxially installed inside the solenoid of the magnetron sputtering coating apparatus. Furthermore, the axial central magnetic field of the solenoid is parallel to the pipe axis. Using the solenoid of the magnetron sputtering coating apparatus, uniform coating can be effectively performed on vacuum pipes with large length-to-diameter ratios, which helps improve the quality of the film.

[0047] S3. Depositing the first layer of film—Au film—on the vacuum pipe: A magnetron sputtering deposition process is used to deposit an Au film on the inner wall of the vacuum pipe. The thickness of the Au film is between 100nm and 500nm.

[0048] Au films have extremely low diffusion coefficients, effectively preventing gas from diffusing from the tube wall material into the vacuum. As a barrier, the Au film reduces the direct interaction between the beam and the tube wall material, thereby lowering the beam bombardment desorption rate and improving the ultimate vacuum and operational stability of the accelerator system.

[0049] The specific steps include:

[0050] S31. Install the high-purity Au target at the central axis of the vacuum pipeline. Furthermore, insulate and fix both ends of the Au target. This installation method ensures uniform and efficient radial sputtering coating on the inner wall of the long, straight pipeline.

[0051] S32. Evacuate the vacuum pipeline and then introduce inert gas into the vacuum pipeline until the gas pressure inside the vacuum pipeline reaches the preset sputtering pressure.

[0052] Specifically, vacuuming can establish a base pressure of less than or equal to 5 × 10⁻⁶ inside the vacuum pipe. -4 The vacuum environment of Pa removes residual gas and impurities from the vacuum chamber to the greatest extent possible, ensuring the purity of the deposited film and preventing impurity atoms from being incorporated into the Au film and affecting its performance.

[0053] Subsequently, a high-purity inert working gas (such as Ar) is introduced and stabilized to a preset sputtering pressure. Argon serves as the sputtering gas; its atoms bombard the surface of the Au target, causing it to sputter atoms. Precise control of the sputtering pressure optimizes the mean free path of the sputtered particles, thereby regulating the energy and motion direction of the deposited atoms, influencing the film's density, grain size, and surface roughness, resulting in excellent gas-getter properties for the Au film.

[0054] Preferably, the pressure of the inert working gas is between 0.1 Pa and 1.0 Pa.

[0055] S33. The solenoid is activated to generate an axial magnetic field inside the vacuum pipe. Simultaneously, a DC negative bias voltage is applied to the Au target, and the vacuum pipe is grounded, creating a radial electric field between the Au target and the vacuum pipe, which excites glow discharge and generates plasma.

[0056] An axial magnetic field helps confine plasma electrons, extending their path near the target material. This increases the probability of collisions between electrons and argon atoms, improving ionization efficiency, stabilizing discharge, and effectively increasing target utilization and deposition rate, while ensuring film uniformity. Consequently, a continuous, uniform, and dense Au film forms on the inner wall of the vacuum pipe under magnetic field confinement.

[0057] Negative bias can accelerate the bombardment of the target material by argon ions, regulate the energy and kinetic energy of the deposited atoms, thereby affecting the microstructure of the film and making the Au film more compact.

[0058] Preferably, the strength of the axial magnetic field generated by the solenoid is between 200 Gauss and 400 Gauss. The DC negative bias voltage applied to the Au target is between -250V and -600V. For example, the solenoid is controlled to generate an axial magnetic field of 200 Gauss, and a DC negative bias voltage of -500V is applied to the Au target.

[0059] S4. Depositing a second film—TiZrV film—on the vacuum pipe: A TiZrV film is deposited on the side of the Au film facing away from the vacuum pipe using a magnetron sputtering deposition process. This step involves depositing a TiZrV film on the surface of the already deposited Au film, using the TiZrV film as the surface layer of the inner wall of the vacuum pipe to form an active getter layer that can provide distributed pumping capability.

[0060] The specific steps for depositing TiZrV films include:

[0061] S41. Stop evacuating the vacuum pipeline, then fill the vacuum pipeline with nitrogen to prevent oxidation of the Au film, and replace the Au target with a TiZrV composite target.

[0062] Understandably, by replacing the target material in a nitrogen environment, the Au membrane can be prevented from being oxidized and contaminated due to exposure to air, thereby ensuring that the active sites of the Au membrane are not affected.

[0063] Preferably, the TiZrV composite target is a long straight rod made by winding Ti wire, Zr wire, and V wire. The atomic ratio of Ti, Zr, and V in the TiZrV composite target is 1:1:1.

[0064] Choosing this atomic ratio optimizes the crystal structure and electronic properties of the TiZrV film, enabling the TiZrV film to have the best adsorption capacity and adsorption rate for active gases, especially hydrogen and carbon monoxide, after activation, thus ensuring high-efficiency gas absorption performance.

[0065] Furthermore, to ensure that the gas-getter capacity of the TiZrV membrane can meet the vacuum maintenance requirements for long-term operation of the vacuum pipeline, its thickness needs to be greater than a certain value. However, if the thickness of the TiZrV membrane is too large, it will also lead to excessive internal stress between the membrane layer and the pipe wall and a decrease in adhesion.

[0066] Therefore, the thickness of the TiZrV film should be controlled between 0.5 μm and 4.0 μm during the TiZrV film deposition process. Within this thickness range, the TiZrV film exhibits a stable film structure and excellent gas absorption performance.

[0067] S42. Evacuate the vacuum pipeline and then introduce inert gas into the vacuum pipeline until the gas pressure inside the vacuum pipeline reaches the preset sputtering pressure.

[0068] Specifically, vacuuming can establish a base pressure of less than or equal to 5 × 10⁻⁶ inside the vacuum pipe. -4 The vacuum environment of Pa is used to remove residual gas and impurities in the vacuum chamber to the greatest extent, so as to ensure the purity of the deposited film and avoid impurity atoms being incorporated into the TiZrV film, which would affect its gas absorption performance.

[0069] Subsequently, a high-purity inert working gas (such as Ar) is introduced and stabilized to a preset sputtering pressure. Argon is used as the sputtering gas; its atoms bombard the surface of the TiZrV composite target, causing it to sputter atoms. By precisely controlling the sputtering pressure, the mean free path of the sputtered particles can be optimized, and the energy and motion direction of the deposited atoms can be controlled, thereby affecting the microstructure of the film (such as grain orientation, density, and internal stress), thus improving the gas-gathering performance of the TiZrV film.

[0070] Preferably, the pressure of the inert working gas is between 0.1 Pa and 1.0 Pa.

[0071] S43. Start the solenoid to generate an axial magnetic field, apply a DC negative bias voltage to the TiZrV composite target, and ground the vacuum pipe to form a radial electric field between the TiZrV composite target and the vacuum pipe.

[0072] Axial magnetic fields help confine plasma electrons, extend their path of motion near the target, thereby increasing the probability of collisions between electrons and argon atoms, improving ionization efficiency, stabilizing discharge, and effectively improving target utilization and deposition rate, ensuring film uniformity.

[0073] After depositing a TiZrV film on the surface of the Au film, an Au / TiZrV composite coating is formed on the inner wall of the vacuum pipe. This coating can effectively block the diffusion of gas from the pipe wall material into the vacuum system by utilizing the dense properties of the Au film, while also allowing the TiZrV film to fully exert its gas absorption efficiency, thereby reducing the beam bombardment desorption rate of the vacuum pipe.

[0074] Negative bias can accelerate the bombardment of the target material by argon ions, modulate the energy and kinetic energy of the deposited atoms, and thus affect the microstructure of the film, such as grain orientation, density, and internal stress, ultimately optimizing the gas absorption performance of the TiZrV film.

[0075] The strength of the axial magnetic field generated by the solenoid is between 200 Gauss and 400 Gauss. The DC negative bias voltage applied to the TiZrV target is between -250V and -600V. For example, the solenoid is controlled to generate an axial magnetic field of 200 Gauss, and a DC negative bias voltage of -450V is applied to the TiZrV target.

[0076] By employing the above steps, a highly active TiZrV film can be formed on the surface of the Au film. After activation, the TiZrV film can provide a powerful distributed pumping rate for active gases such as H2, CO, CO2, and N2 at room temperature, thereby significantly reducing the static outgassing rate of the vacuum pipeline and greatly improving the ultimate vacuum level of the vacuum pipeline, which is key to achieving an ultra-high vacuum environment.

[0077] The TiZrV film and Au film work synergistically to form a dense barrier layer on the surface of the vacuum pipe to prevent the pipe wall material from escaping into the vacuum environment, and to form an active getter layer on the surface of the Au film to adsorb active gas molecules in the vacuum chamber. This reduces the beam bombardment desorption rate of the vacuum pipe, making it particularly suitable for particle accelerator systems with extremely high vacuum performance requirements.

[0078] In addition, in another embodiment of the present invention, a vacuum conduit is described.

[0079] The vacuum pipe is coated with a composite coating consisting of an Au film and a TiZrV film. The composite coating is prepared using the method described in the above embodiments for preparing a composite coating on the inner wall of the vacuum pipe.

[0080] like Figure 3 As shown, the composite coating structure on the inner wall of the vacuum pipe is as follows: the bottom layer is an Au film, and the top layer is a TiZrV film. This vacuum pipe combines the dense barrier properties of the Au film with the strong gas-gathering capacity of the TiZrV film. The Au film effectively blocks the diffusion of substrate gas into the vacuum chamber, solving the bottleneck problem that existing TiZrV coatings cannot completely block the diffusion of hydrogen gas from the substrate. At the same time, the roughening treatment increases the effective specific surface area of ​​the TiZrV film, improving its gas-gathering capacity and pumping speed.

[0081] In this invention, by depositing an Au / TiZrV double-layer film on the inner wall of the vacuum pipe, a double-layer structure of a dense barrier layer and an active gas-getting layer is formed on the surface of the vacuum pipe. This not only utilizes the dense properties of the Au film to effectively block the diffusion of gas from the pipe wall material into the vacuum system, but also allows the TiZrV film to fully exert its gas-getting efficiency, thereby reducing the beam bombardment desorption rate of the vacuum pipe.

[0082] In the description of the embodiments of the present invention, it should be noted that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of the present invention. In addition, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0083] In the description of the embodiments of the present invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of the present invention based on the specific circumstances.

[0084] In embodiments of the present invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0085] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms are not limited to the same embodiments or examples. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Furthermore, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0086] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a composite coating on the inner wall of a vacuum pipe, characterized in that, include: The inner wall of the vacuum pipe is roughened. The processed vacuum pipe is coaxially installed inside the solenoid of the magnetron sputtering coating device. Au film is deposited on the inner wall of a vacuum pipe using a magnetron sputtering coating process. The thickness of the Au film is between 100 nm and 500 nm. A TiZrV film was deposited on the side of the Au film facing away from the vacuum tube using a magnetron sputtering deposition process. The thickness of the TiZrV film was between 0.5 μm and 4.0 μm. The specific steps included: Stop evacuating the vacuum pipe, then fill the vacuum pipe with nitrogen to prevent Au film oxidation, and replace the Au target with a TiZrV composite target; The vacuum pipeline is evacuated, and then inert gas is introduced into the vacuum pipeline until the gas pressure inside the vacuum pipeline reaches the preset sputtering pressure. The solenoid is activated to generate an axial magnetic field. A DC negative bias voltage is applied to the TiZrV composite target, and the vacuum pipe is grounded to create a radial electric field between the TiZrV composite target and the vacuum pipe.

2. The method for preparing a composite coating on the inner wall of a vacuum pipe according to claim 1, characterized in that, The specific steps for depositing an Au film on the inner wall of a vacuum pipe using magnetron sputtering coating technology include: Install the Au target at the center axis of the vacuum pipeline; The vacuum pipeline is evacuated, and then inert gas is introduced into the vacuum pipeline until the gas pressure inside the vacuum pipeline reaches the preset sputtering pressure. The solenoid is activated to generate an axial magnetic field. A DC negative bias voltage is applied to the Au target, and the vacuum pipe is grounded to create a radial electric field between the Au target and the vacuum pipe.

3. The method for preparing a composite coating on the inner wall of a vacuum pipe according to claim 1 or 2, characterized in that, The roughening treatment of the inner wall of the vacuum pipe includes: The inner wall of the vacuum pipe is roughened by at least one of the following methods: sandblasting, chemical etching, and mechanical threading.

4. The method for preparing a composite coating on the inner wall of a vacuum pipe according to claim 3, characterized in that, The strength of the axial magnetic field generated by the solenoid is between 200 Gauss and 400 Gauss, and the DC negative bias voltage applied to the Au target or TiZrV composite target is between -250V and -600V.

5. The method for preparing a composite coating on the inner wall of a vacuum pipe according to claim 3, characterized in that, The pressure of the inert gas inside the vacuum pipe is between 0.1 Pa and 1 Pa.

6. The method for preparing a composite coating on the inner wall of a vacuum pipe according to claim 3, characterized in that, The TiZrV composite target is made by winding Ti, Zr, and V elemental wires in an atomic ratio of 1:1:

1.

7. A vacuum pipe, characterized in that, The inner wall of the vacuum pipe is provided with a composite coating, which is made by the method for preparing a composite coating on the inner wall of the vacuum pipe as described in any one of claims 1 to 6.

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