Ion pumps to prevent metal gas poisoning

Abstract

An ion pump that protects against metal gas poisoning has a design added to its output connecting pipe to prevent contamination of the ion pump. This invention not only significantly reduces the amount of metal gas that enters the pump body, but also has no significant effect on the pumping speed of the ion pump, thereby isolating and protecting the ion pump, extending its service life, and reducing the ion current background of the ion pump. Furthermore, by reducing the amount of impurity particles generated during the sputtering ion pump's operation that enter the target vacuum system, a higher vacuum level can be achieved in the target area. The device has a simple structure and is easy to implement, and can be used as an ion pump device for vacuum pumping in experimental systems requiring ultra-high vacuum levels.

Description

Technical Field

[0001] The invention relates to vacuum technology, in particular to a novel ion pump capable of preventing metal gas poisoning. Background Art

[0002] As scientific experiments develop towards more precise atomic fields, ultra-high vacuum is increasingly used in industry and scientific research. As an experimental platform for precision measurement, it is often used in scientific experimental systems that require high vacuum, especially in the field of atomic and molecular physics experiments. The atomic substances used in these experimental platforms are mostly alkali metals, such as rubidium, potassium, cesium and other alkali metals, and the required vacuum degree is generally 10 -7 Pa-10 -9 Pa.

[0003] The sputtering ion pump is mainly based on the principle of high-voltage ionization of gas molecules. The ion pump is mainly composed of four parts: the anode, the cathode, the permanent magnet and the pump body. The pumped gas molecules or atoms are ionized under high voltage to form charged ions. Under the action of the electric field, the gas ions are prompted to move toward the cathode and are transported to the cathode adsorption surface of the pump. The cathode plate material is titanium metal. After the titanium metal is impacted and sputtered, an active titanium film is continuously formed on the inner wall of the cavity, which continues to react with the gas molecules, thereby continuously exhausting. The sputtering ion pump has no moving mechanism and is a truly oil-free, vibration-free, noiseless ultra-clean vacuum pump. The ultimate pressure obtained can reach 10 -7 Pa-10 -9 Pa.

[0004] Typically, the anode of an ion pump is a honeycomb structure consisting of multiple stainless steel cylinders arranged in an array, and the cathode is two parallel titanium alloy plates that sandwich the anode in the middle. The three are kept at a certain distance from each other and connected by high-voltage insulating ceramics.

[0005] The ion current in each honeycomb structure of the ion pump is proportional to the gas pressure. There is a gap between the cathode and anode arrays of the ion pump. When the ion pump is working, metal impurity particles in the system can pass through the honeycomb structure through this gap and impact the inside of the ion pump. If ion pump protection measures are not taken in the vacuum system, the high-voltage insulating ceramic of the ion pump may be contaminated by the alkali metal gas in the system. As the alkali metal gas entering the ion pump increases, the metal gas is deposited on the insulating ceramic, which may cause the cathode and anode of the ion pump to be conductive, which will reduce the pumping performance of the ion pump and increase the ion current background of the ion pump. At the same time, the contamination of the ion pump will also shorten the service life of the ion pump.

[0006] Generally, there are two measures to protect ion pumps. One is to heat the ion pump to reduce the deposition of metal gas in the ion pump; the other is to install a gas barrier device in the ion pump to reduce the entry of metal gas into the ion pump. However, if the protective measure of heating the ion pump is taken, the temperature increase of the ion pump will cause the metal gas adsorbed on the titanium cathode to desorb, resulting in the inability to effectively reduce the vacuum degree. At the same time, heating may cause inter-electrode glow discharge and increase the pressure of the system. In severe cases, it will also affect the normal operation of the pump. The barrier devices generally installed in the ion pump will block the light between the ion pump and the system, so they are also called optical shielding. Although this shielding can reduce the gas ion flow between the system and the ion pump, it will also cause the ion pump pumping rate to decrease, affecting the vacuum effect. Therefore, it is necessary to carefully evaluate the shape and position design of the partition device to achieve the best vacuum effect. Summary of the Invention

[0007] To overcome the shortcomings of the aforementioned ion pump poisoning prevention measures, the present invention provides an ion pump that effectively isolates the alkali metal gas flow entering the ion pump. Compared to the aforementioned solutions, this device not only significantly reduces the metal gas flow entering the pump body, but also has no significant impact on the pump's pumping speed, thereby extending the ion pump's service life and reducing the ion current background of the ion pump, achieving the desired isolation and protection of the ion pump. The device has a simple structure and is easy to weld and install, without adding any additional burden to the scientific experiment platform.

[0008] The technical solutions of the present invention are as follows:

[0009] An ion pump that prevents metal gas poisoning is characterized by a structure for preventing ion pump contamination added to the output connecting pipe of the sputtering ion pump. The structure comprises two or more sets of porous structure baffles fixedly placed in the connecting pipe via a vacuum flange, a metal base, and a metal ring. The porous structure baffles are formed by digging several arc-shaped ladder-shaped holes or other shaped holes in a circular porous structure in the radial direction. When the two or more sets of porous structures are fixed, the small holes of the porous structures are kept in a non-directly aligned position and are staggered, so that alkali metal gas or other working substances cannot directly enter the interior of the ion pump through the small holes.

[0010] The distance between the two groups of porous structure metal sheets is determined by the length of the metal ring.

[0011] The pore sizes of the two groups of porous structures are determined by the working material of the vacuum system. For example, for alkali metals, the pore size is generally between 1-100 μm.

[0012] When the metal gas poisoning-proof ion pump is in use, the output port of the connecting pipe is connected to the multi-channel through a pipe connecting flange.

[0013] The porous structure designed in the invention is assembled in the connecting channel between the novel ion pump and the vacuum system.

[0014] The main structure of the sputtering ion pump includes an absorbent cathode plate, an anode cylinder, a shell, an electrical lead, insulating ceramics, a strong permanent magnet, a connecting pipe and other accessories. The basic principle of the ion pump is to use cathode discharge to generate positive ions of gas molecules. The ions collide with the cathode and are captured by the cathode, and a sputtering effect is also produced. When in use, a high voltage is first applied between the anode and cathode. Under the action of the high voltage, the gas molecules are ionized. At the same time, under the action of the electromagnetic field, the gas ions are prompted to move toward the cathode, bombarding the cathode plate of the ion pump. The cathode plate material is metallic titanium. After the metallic titanium is sputtered by the impact, an active titanium film is continuously formed on the inner wall of the cavity, which continues to react with the gas molecules, thereby continuously exhausting and removing the active gas. Due to the presence of the magnetic field, the cathode discharge can be maintained at an extremely low pressure.

[0015] The present invention does not protect the shape and length of the anode cylinder. The pump body of the ion pump for preventing metal gas poisoning of the present invention can be a general ion pump.

[0016] The barrier device used in the metal gas poisoning-resistant ion pump of the present invention is a porous plate. This plate is installed in the pipe connecting the pump body to the vacuum system and secured with a metal ring and a metal base. The plate has smooth inner and outer walls and uniform pores, offering excellent properties such as shape stability, high strength, high temperature resistance, corrosion resistance, and impact resistance. Furthermore, its excellent air permeability makes it well-suited for use in vacuum pipes.

[0017] In the present invention, in order to fix the porous structure offset sheet, it is necessary to weld a fixed base in the vacuum pipe. After the first porous sheet is placed, a metal ring is used to separate the two porous sheets at a designed distance and the base of the second porous sheet is welded. Note that the small holes of the two porous structure porous sheets must be staggered and then welded and fixed.

[0018] Compared with the prior art, the technical effects of the present invention are:

[0019] (1) The ion pump of the present invention has a porous structure fixedly placed in the pipeline connecting the ion pump and the system. Due to its large surface area, it can adsorb metal gas and has small holes. Compared with the previous pipeline barrier device, it can not significantly affect the ion pumping rate, and the ultimate pressure can reach 10 -9 Below Pa.

[0020] (2) At the same time, due to the barrier effect of the porous structure plate with staggered small holes, compared with not installing the plate, the metal gas entering the ion pump is greatly reduced after the porous structure plate is installed, and the ion flow can reach the pA level. The pollution of the ion pump by the extracted metal gas is significantly reduced, indicating that the shielding effect of the device of the present invention can very effectively reduce the particle flow intensity of the ion pump, improve the vacuum effect of the experimental system, and extend the service life of the ion pump.

[0021] The ion pump of the present invention is small in size and has a long service life. It can improve the vacuum degree of the experimental system, has a simple structure, is easy to weld and install, and has stable performance, and meets the requirements of space atomic physics experimental tasks that require high vacuum degree. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a cross-sectional view of the ion pump invented to prevent metal gas poisoning.

[0023] Among them, serial numbers 1 and 2 are porous metal sheets; serial number 3 is a fixed metal ring; serial numbers 4, 5, and 6 are fixed metal bases; serial number 7 is the anode cylinder; serial number 8 is the cathode plate; and serial number 9 is insulating ceramic.

[0024] Figure 2 This is a cross-sectional view of two sets of porous metal sheets and a diagram of their dislocation placement.

[0025] Figure 3 This is a structural diagram of the embodiment of the ion pump for preventing metal gas poisoning after installation. DETAILED DESCRIPTION

[0026] The present invention will be further described below with reference to implementation examples and drawings, but this should not limit the scope of protection of the present invention.

[0027] Example: Metal gas poisoning-proof ion pump with two sets of porous structured staggered metal sheets

[0028] The inner diameter of the vacuum pipe is 15.2 mm. The porous sheet is made of stainless steel and consists of a circular porous structure with several radially cutout arcuate, stepped holes or other shaped holes. The pore size of the porous structure is 30 μm. The two sets of porous metal sheets have a diameter of 15 mm and a thickness of 1.0 mm. The distance between the two sets of porous metal sheets is 4 mm, and the openings are offset by 60°. The gas to be pumped is rubidium vapor, and the ion pump is the metal gas poisoning-resistant ion pump described in the present invention.

[0029] See Figure 1 . Figure 1This is a cross-sectional view of the metal gas poisoning prevention ion pump of the present invention. In the embodiment, in order to fix and install two sets of porous metal sheets, it is necessary to weld the fixed metal ring 3 and the fixed metal base 6 in the vacuum pipe. After installing the first porous metal sheet 2, the fixed metal base 5 is welded to firmly fix the porous metal sheet. Then, the second porous metal sheet 1 is installed. Note that the small holes 1 and 2 need to be staggered. Finally, the fixed base 4 is welded to firmly fix the porous metal sheet 1. In this specific embodiment, the distance between the two porous metal sheets is 4mm, and the staggered angle of the openings is 60°. See Figure 2 .

[0030] The connecting pipe port of the metal gas poisoning prevention ion pump of the present invention is connected to the multi-channel through a flange. Figure 3 , install the rubidium source, heating tape, thermometer and ion pump, refer to Figure 3 , where serial number 10 is the ion pump of the present invention, serial number 11 is the rubidium source, and serial number 12 is the heating belt. The system and the rough pump pipeline are baked and pre-pumped. After the pipeline is gradually cooled down, the molecular pump is pumped to the molecular pump limit of 10 -6 Pa. The system and ion pump temperature are maintained, the rubidium source is broken, the vacuum becomes worse, and the molecular pump continues to pump until 10 -6 Pa. Then, turn on the ion pump and gradually lower the system and ion pump temperatures to room temperature. Then, bake out the rubidium source to allow rubidium vapor to enter the vacuum line. Monitor the ion pump's ion flow, rubidium source temperature, and system temperature.

[0031] During the system bake-out process, the ion pump readings were observed. Afterward, without changing any other components except the porous metal dislocation sheet, the sheet was replaced with a porous metal long through-hole sheet and a ceramic long through-hole sheet of the same size. The system was baked at the same temperature, and the ion pump readings were observed during the three test runs. During the longer observation period, the ceramic long through-hole sheet activated the protection state the fastest when connected to the ion pump test, indicating that the ion pump had already begun to poison. After a period of baking, the porous metal long through-hole sheet also activated the protection state and began to poison.

[0032] The above results show that the new ion pump design with porous metal dislocation holes in the present invention achieved the best results, indicating that the ion pump of the present invention that is resistant to metal gas poisoning, due to the effect of the added porous metal dislocation holes, will have a certain barrier effect on the metal conductive gas entering the ion pump, which can not only greatly reduce the metal gas entering the pump body, but also has no significant effect on the pumping speed of the ion pump, reducing the ion current background of the ion pump, which is beneficial to improving the vacuum effect of the experimental system and extending the service life of the ion pump.

Claims

1. An ion pump that prevents metal gas poisoning, characterized in that a structure is added to the output connecting pipe of the ion pump to prevent ion pump contamination. The structure comprises two or more sets of porous structure baffles fixedly placed in the connecting pipe via a vacuum flange, a metal base, and a metal ring. The porous structure baffles are formed by cutting out several arc-shaped ladder-shaped holes in the radial direction of a circular porous structure. When the two or more sets of porous structure baffles are fixed, the arc-shaped ladder-shaped holes of the porous structure are kept in a non-directly aligned position and are staggered to prevent alkali metal gas from directly entering the interior of the ion pump through the small holes.

2. The ion pump for preventing metal gas poisoning according to claim 1, characterized in that: The distance between the two or more groups of porous structure baffles is determined by the length of the ring.

3. The ion pump for preventing metal gas poisoning according to claim 1, characterized in that: The pore sizes of the two or more groups of porous structure baffles are determined by the working material of the vacuum system.

4. The ion pump for preventing metal gas poisoning according to claim 3, characterized in that: When the working substance is alkali metal gas, the pore size is between 1-100 μm.

5. The ion pump for preventing metal gas poisoning according to claim 1, characterized in that: The structure for preventing the ion pump from being contaminated is assembled in the connection channel between the ion pump and the vacuum system.

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