The Use of Single Lenses in the Radio Frequency Mass Spectrometers

Author Name(s): T. Daumenov, M. A. Khizirova, A. S. Baikenov, A. O. Kassimov, S. T. Amanzholova
Author Email: dautl@mail.ru

Abstract

The possibility of using a single lens to increase the resolution of the radio-frequency mass spectrometer is shown. The problem is solved by calculating the additional energy of ions when they pass through the electrostatic field of a single lens with rotational symmetry.

Keywords Single Lens Selecting Cascade, Radio-Frequency Mass Spectrometer, An Increase of Energy Resolution, Ion Flux

Introduction

Radio-frequency mass spectrometers (RFMS) [1] are known, which are used to analyze the ion and molecular composition of the upper atmosphere (figure 1), to measure partial pressures in vacuum technology. A typical node of these devices is a selection cascade, consisting, as a rule, of three plane-parallel grids ( 4 32 , , C CC ), located at an equal distance s from each other, which are fed negative accelerating voltage U, and the middle grid ( 3 C ) and high-frequency sinusoidal voltage with amplitude . Between the cathode K and a grid accelerates ions of the applied voltage. While passing the ion beam through selecting cascade, depending on the speed of the ions change their energy. Indeed, if the ions are accelerated when moving in the region between the second and third grids, and after passing through the third grid, its potential will change so that the ions between the third and fourth grids will also accelerate, then they will receive additional energy at the output of the system. The problem is that at a given accelerating voltage on the grids and the frequency of alternating voltage , the ions of a certain mass mand charge q passing through the selection stage, acquire the greatest increase in energy . In order for the ions to get the maximum energy, it is necessary that their time of flight is quite certain and the phase of flight to the area between the second and third grids is optimal.

 

Conclusion

Thus, the disadvantage of the analyzer of the radio-frequency mass spectrometer of the three-grid selection stage is the fact that the grids are a mechanical obstacle in the way of ions [3,4,5]. In a single-stage mass spectrometer analyzer, ions pass through the grids at least three times, and even for grids with very good transparency, the total transparency of the cascade decreases to 50%. Near the grid cells, there is also a sagging of equipotential surfaces, which have a scattering effect on the ions. These factors affect the sensitivity of the device, in the end, and its resolution. In addition, during the operation of the grid can be contaminated and covered with a thin film, which will lead to uncontrolled operation of the mass spectrometer.

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