Research On Test Method Of Minimal Pumping Speed Of Micro Sputtering Ion Pump

In recent years,with the in-depth development of aerospace science and technology,the use of micro-sputter ion pumps has become more and more widespread.The space mass spectrometer used in deep space exploration,cesium atomic clock used in navigation and positioning and other military products in China all need a micro sputtering ion pump to maintain the high vacuum inside the system.Moreover,there are strict requirements for the pumping speed index provided by the micro sputter ion pump.However,the test method of the pumping speed currently widely used in the world cannot accurately test the minimal pumping speed of the micro sputter ion pump,which seriously affects the performance of related products and the development of the basic science of vacuum metering.Based on this,this paper studies the test method of the minimal pumping speed of the micro sputtering ion pump.First of all,through the comparative analysis of the minimal pumping speed and the large pumping speed,it is found that the test of the minimal pumping speed has the following three difficulties:the first is to provide a small flow and accurately test;the second is that when testing the minimal pumping speed,the pumping effect of the extractor ionization gauge cannot be ignored;the third is to put forward higher requirements for the overall performance of the test device.Combined with the current test method of the pumping speed,two test methods are proposed,namely the improved dynamic conductance method and the improved flowmeter method.Secondly,the experimental tests are carried out on specially designed pumping speed test devices.On the one hand,by repeating the operation of baking,leak detection,etc.,the ultimate vacuum of the test chamber R1 is 4.28×10-7 Pa,the ultimate vacuum of R2 is 2.84×10-7 Pa,and the ultimate vacuum of R3 is 3.71×10-7 Pa.The maximum outgassing rate of the test chamber R1 is 7.8×10-11 Pa·m3/s,and the maximum outgassing rate of the test chamber R3 is 6.2×10-11 Pa·m3/s,which makes the performance of the experimental device reach the test requirement of minimal pumping speed,and solves the test difficulty three;On the other hand,the method of static pressure change is used to test the conductance of the micro flow gas supply system,and the test result of the conductance is verified to ensure the accuracy of providing the micro flow and solves the test difficulty one.Then,the improved dynamic conductance method and flowmeter method are used to tese the minimal pumping speed of a kind of micro sputtered ion pump sample,both of which eliminate the interference of the test difficulty two to the test results.The test results show that the pumping speed of the sample pump tested by the two methods increases first and then decreases with the increase of gas pressure;the pumping speed of the sample pump tested by the two methods is roughly proportional to the test voltage.In the improved dynamic conductance pumping speed test,the uncertainty of the test pumping speed is 7.1%,which effectively reduces the uncertainty.In the improved flowmeter method,the pumping speed and outgassing rate of the extractor ionization gauge are also tested.The test results show that as the gas pressure in the test chamber increases,the pumping speed of the extractor ionization gauge shows a downward trend,while the gassing rate shows an upward trend.At the same time,the test results are brought into the pumping speed calculation formula,and the minimal pumping speed of the test is corrected,and the test accuracy is improved by about 6.3%.Finally,under the condition of nitrogen as the test gas,the derivation process of the theoretical calculation of the pumping speed of the sample pump is explained,and the pumping speed of the sample pump calculated theoretically is compared with that measured by the improved flowmeter method.The results show that the theoretical pumping speed is significantly smaller than the experimental pumping speed,with a difference of about 20%,and the causes of the errors are analyzed.Through the research on the test method of the minimal sputtering speed of the micro sputter ion pump,the problem that the micro sputter ion pump in the space mass spectrometer,the helium atomic clock and the traveling wave tube cannot accurately test the minimal pumping speed can be solved,which ensure the smooth development of major engineering projects such as deep space exploration,space station and Beidou navigation in China.In addition,accurately measuring the minimal pumping speed of the micro-sputtering ion pump can expand the vacuum metering parameters and enhance the international status of vacuum metering in China,with obvious social benefits.