Research On Key Techniques Of Miniature Mass Spectrometer Used For Lunar Exploration

Mass spectrometry is an approach to identify unknown substance by obtaining the information of molecular weight and molecular structure. It is a major spectroscopic method in analytical chemistry and parallels with optical spectrum and nuclear magnetic resonance. Large-scale mass spectrometer is now widely used in food safety, life science, pharmaceutical, chemical industry, military affairs, national defense, and other trace or trace substance detection applications. With the development of space technology, it has been miniaturized and used in the extraterrestrial planets detector. Miniaturized mass spectrometer is now the standard instrument in foreign aerospace detector. With the increase of China's overall strength and the gradual implementation of man-made space flight and lunar exploration projects, the need for miniaturized mass spectrometers is extremely urgent. This paper is based on the project'The Miniaturized Lunar resource exploration mass spectrometry'and will research on the key techniques of mass spectrometer's miniaturization.First, the basic theory of ion trap mass spectrometer has been studied. How to improve the instrument sensitivity is explained from perspectives of ion energy and pseudo-potential. On this basis, the research on the problem of the difficulty to analyse the small molecule in the trap has found that the root problem is the impact of anharmonicity oscillator potential within the ion trap on the instability of low mass ions below 20. It is the smaller ion trap size that causes the stronger anharmonicity oscillator potential. Therefore, a view to design ion trap is put forward.that is, to increase the size of the ion trap and improve radio frequency.Second, the basic principle of ion trap design has been discussed. Under the premise of ensuring the signal sensitivity, small size, low power and low weight are needed. Following this guidelines, the design of CIT ion trap is optimized along with previous experimental results. Ion trap has six size parameters, which leads to a time consuming simulation. Combined with Prof. COOKs'optimization theory and practical engineering needs, conclusion of optimizing parameters z0 is arrived. This can significantly reduce computing time. Many documents take'the percentage of four pole field in high-pole field is -10%'as the optimization criterion by experience, because it can improve the system resolution. Combined with experimental results and the characteristics that the molecular analysed is too small, the optimization criterion of minimizing high pole field is proposed. Finally, combined with the current technological level, a practical optimization method is given.Later, as the circuit size and power consumption of the traditional commercial mass spectrometer are relatively large and the weight is also relatively high, a variety of alternative technical solutions combineds with performance index of miniature mass spectrometer used for lunar exploration are used to reduce the size, power consumption and weight in the design of circuits, which include the following methods: As the magnetic ring transformer is of small transformer loss, the air core transformer of commercial mass spectrometers could be replaced by it to achieve satisfactory results in power dissipation and size. Using the frequency synthesis technology produces the arbitrary adjustable parameters of the RF small signal to replace the method of generating signal by NI card with high power consumption. At the same time, research on ROM table's compression method in frequency synthesis provides a better compression method in theory and this new method is implemented in the FPGA to solve the problem of no space-level frequency synthesizer chip. According to the experiment, the micro-current amplification circuit is optimized to reduce the size and power consumption. By the rational optimization design, the whole control system of the mass spectrometer are integrated in a circuit board, which includes data acquisition, data transmission, signal generation, power amplification and other functions, and substantially reduces the volume, power consumption and weight of the whole system.Finally, the experimental platform is built with pre-designed circuit, ion trap and associated with relevant equipment. Methyl salicylate, methane, hydro- gen, helium and the mixture of hydrogen and helium gas have been measured on the platform, and the relevant experimental phenomena have been explained. The related theories are verified by helium that pseudo-potential and q z have impact to the sensitivity of the apparatus. And this experiment provides a set of good experimental parameters for engineering applications.