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Title: A study of the quadrupole mass spectrometer for operation in hostile environments.
Author: Yang, J. M.
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 1985
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The aim of the project described in this thesis was to develop an analytical measuring instrument for use as a residual gas analyser in industrial vacuum systems. The quadrupole mass spectrometer was chosen operating in a new and as yet not fully tested mode. In this novel mode, only a. c. voltages are applied to the rods and a special collection system using energy and spacial filtering is employed (so called the a. c. mode). This is in contrast to the normal mode, where a. c. and d. c. voltages are applied to the rods, and a simple plate or an electron multiplier collector is used. This thesis describes a series of experiments to investigate the properties of the quadrupole mass filter in the a. c. mode when operating in hostile environments. To carry out this investigation a small vacuum furnace was built and charged with workshop swarf and viton gaskets. The sensitivity of a 50 mm quadrupole mass filter operating in the a. c. mode was observed to fall by 40% after 100 hours of operation at 10-3 mbar in the above gases. However, the relative sensitivity over the mass range 10- 100 a. m. u. remained the same. In a separate set of experiments the relative sensitivity of an 85 mm quadrupole mass filter was examined in the a. c. mode. The ratio of singly to doubly charged ions for argon and krypton changed by 15% or less after 50 hours contamination. This is in complete contrast with that of the normal mode. In the normal mode instability caused by even minor comtamination was always observed. There is shown in the thesis to be a theoretical basis for this difference. It was verified that heating the source to 200°C and sweeping the ion energy to relatively high value for high mass successfully aided the development. In addition, the use of a Nier type source, high pressure limitation, and multi-peaks were also investigated. The Nier source was found to provide an improved ion beam, enabling good resolution to be achieved. The high pressure limit of a quadrupole mass filter in the a. c. mode was found to be 10-4 mbar. The multi-peaks were shown to be a fundamental phenomenon which could be avoided when operating with normal ion energy. The resolution of a quadrupole mass filter in the a. c. mode was found to be proportional to the power 2.3 of the number of cycles ions spent in quadrupole field.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Chemical engineering Chemical engineering