Non-evaporable getter in the mini ion pump (Figure)
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December 16 09:06:43, 2022
In order to ensure the high reliability and long life of the small-sized ultra-high vacuum sealing device, a Mini-Combination Ion Pump with a non-evaporable getter has been developed. In the newly built miniature ion pump performance testing system, the effect of non-evaporable getter on the device storage and micro-ion pump start-up characteristics was studied. The simulation of the actual situation when the mini ion pump and the miniature vacuum device are integrated into one may encounter different gas loads, and the possible applications of the new results are discussed. Text: High reliability, long life, small ultra-high vacuum sealed devices have been widely used in many important areas. The smaller the size of the device, the higher the requirements for vacuum sealing, and the successful promotion of the MS leak detection technology toward ultra-sensitivity (better than 1 × 10-13 Pa · m3 / s). At the same time, high temperature baking before sealing to go must also be reliably guaranteed. After long-term choice and development, ion pumps (IonPumps, referred to as IP) has been miniaturized, developed a series of products. It is a compact vacuum pump that can vent over a wide range of pressures, with a high pumping speed relative to its volume, and a relative vacuum gauge whose ion flow indicates the degree of vacuum. Miniature ion pumps have been integrated with many practical small vacuum devices to make them highly reliable, long-life operation safeguards. For those who do not allow high-temperature baking to practical vacuum device, is even more indispensable. Noting the rapid development of Getters and in particular the continuous development of non-evaporable Getters (NEG) films by CERN (European Center for Particle Physics) since 1995, large-scale The exit surface in the accelerator is converted to the suction surface and a major breakthrough has been made. In recent ten years, various types of ion / getter combination pumps (Ion / GetterCombinationPumps) have been developed in large ion pump products at home and abroad. We successfully developed a miniature ion pump, integrated with a small ultra-high vacuum container as one of the applications, had encountered after storage for some time, due to accumulated gas pressure caused by excessive increase in micro-ion pump than the start-up pressure, and So that the entire device scrapped and other practical problems. Taking into account the newly developed low-temperature activated SAES SAFETY non-evaporable getter is suitable for long-term application in the case no longer exposed to atmospheric pressure after sealing, the prospect of forming a high-performance composite pump with a miniature ion pump, it is worth to be explored. Attention has not yet been seen at home and abroad have been miniature composite ion pump, that is with a non-evaporable getter miniature composite ion pump (Mini-CombinationIonPumpswithNEG) or miniature ion / non-evaporable getter composite pump (Mini-Ion / NEGCombinationPumps) related reports, two years ago has completed the design and preliminary experimental study of this new pump, this article is in the new micro-ion pump test system, non-evaporable getter in the application of micro-ion pump in the latest Results and discussion. 1, Experiment 1.1, Miniature compound ion pump composite pump is composed of non-evaporable getter and micro-ion pump. St172 NEG produced by Italy SAES Company is selected. Adopt the high mesh stainless steel mesh sieve to get the getter particles wrapped and welded to the outside of the anode cylinder. The test results show that the structure neither drops powder nor affects the pumping speed. 1.2, NEG activation St172 recommended low-temperature activation conditions are better than 10-1Pa vacuum or ultra-pure inert gas heated to 400 ℃ for half an hour, the minimum activation temperature from 200 ℃ start. NEG was activated at 250 ℃ for three hours and 350 ℃ for half an hour respectively, and the pumping speed was measured. The results show that at 250 ℃, the measured pumping speed is still very low even after three hours of activation. The result at 350 ℃ for half an hour is much better than the former, which is close to the recommended result. Therefore, all the tests for NEG in this paper adopt the recommended conditions activation. After repeated experimental studies to solve the recommended conditions for micro-composite ion pump local warming to activate NEG program. 1.3, Miniature ion pump performance test system As the ion pump test standards at home and abroad are only applicable to pumping speed greater than 10L / s ion pump, the newly developed miniature ion pump pumping speed two orders of magnitude lower, only a few L / s, it is necessary to establish an oil-free ultra-high vacuum system consisting of molecular pump, ion pump and dry pump to reduce the system background. With reference to the existing test methods at home and abroad and the experience of micro-ion pump performance testing, a new mini ion pump performance testing system was newly established. Figure 1 highlights the pumping speed and pressure testing chamber, which can be used for pumping speed, With the pressure relationship, the maximum start-up pressure and ultimate pressure and other important performance tests, the system is equipped with a quadrupole mass spectrometer to monitor the partial pressure and achieve ultra-sensitivity leak detection. Results and discussion 2.1. The effect of NEG on the storage of miniature ion pump and miniature vacuum device In the left side pressure test chamber, only the low temperature baking was conducted to simulate the experimental conditions of more severe outgassing during storage, The device was tested for NEG pressure changes over time under both conditions, as shown in Figure 2. 27 days after the absence of getter pressure rose to 4.5Pa, the same conditions, the fully activated getter can be stored for 28 days after the pressure rose to only 1.4 × 10-3Pa, the degree of vacuum increased more than three orders of magnitude. NEG, when activated well, has a higher pumping speed at a lower pressure than the ion pump and is effective in pumping off gases such as H2, CO, and CO2, which effectively improves the performance of sealed devices during storage Vacuum quality significantly extends the shelf life and lifetime of the device. In the absence of a getter, the pressure in the device will approach or exceed the activation pressure of the ion pump in the absence of a getter, while the getter maintains a high vacuum in the device. Significantly improve the storage characteristics of the device is NEG's main function. 2.2, NEG micro-ion pump start-up characteristics of 2.2.1, NEG-free micro-ion pump startup characteristics Mini ion pump and small vacuum devices integrated purpose is to ensure that its ultra-high vacuum. Because inevitable outgassing can cause pressure build-up during long-term storage and operation, the ion pump initiates aspiration by powering in the hope of quickly reaching the desired level of vacuum, for example, less than 5.0 × 10 -5 Pa within a half-hour. In the pressure test chamber shown in Figure 1 were filled with P0 0.9, 2.5 and 5.1Pa dry air, used to simulate the long-term storage of different levels of total outgassing, the micro-ion pump start under these conditions, start-up characteristics The experimental results of pressure changes are shown in Table 1. When P0 is 0.9Pa, the ion pump can be started smoothly and drops to less than 5.0 × 10-5Pa in 30min. When P0 is 2.5Pa, the ion pump can be started after multiple ignitions, and can drop below 30min 5.0 × 10-5Pa; When P0 is 5.1Pa, it is higher than the ignition pressure and can not be started. Table 1 Miniature ion pump pressure changes at start-up The experimental results show that: Without NEG, the ion pump can either start in a short time, pumping within half an hour 5.0 × 10-5Pa or can not start. Miniature ion pump can not start above the fire pressure, will lead to the entire device scrapped, should try to avoid it. 2.2.2 Start-up Characteristics with NEG Miniature Compound Ion Pump When the pressure test chamber is filled with dry air and used to simulate long-term storage, the equilibrium pressure P0 is 9.6 × 10-5 and 1.2 × 10-3 and 5.8 × 10-3Pa, the start-up characteristics of the ion pump, after starting pressure changes. The experimental results show that: (1) The composite ion pump can not only start smoothly under the pressure of 10-4Pa or P0, but also can quickly enter the ultrahigh vacuum , Which corresponds to the situation of the vast majority of normal sealed devices. When the gas load is light, the vacuum performance of the device is reliably guaranteed. (2) The composite ion pump can still start smoothly under the pressure of 10-3Pa, and also meets the requirement of pumping the pressure to less than 5 × 10-5Pa in half an hour. This corresponds to a heavy gas load. Please note that after 5h, the pressure should be further pumped to 3.8 × 10-5Pa. (3) In P0 is 5 × 10-3Pa pressure, the composite ion pump can start, but can not meet the pressure within half an hour pumped below