The Theory of the Modified Aston-Type Mass-Spectrometer

Citation

Munro, George Clarkson (1933) The Theory of the Modified Aston-Type Mass-Spectrometer. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/2X6A-V938. https://resolver.caltech.edu/CaltechTHESIS:02282017-085047751

Abstract

The theory of an Aston-type mass-spectrometer using a cylindrical condenser and bringing all ions of the same specific mass to a point focus by variation of the magnetic field alone is developed. The theory of the motion of an ion in an inverse first-power electrostatic field is studied under the particular set of conditions where all ions regardless of their energy enter the condenser normal to its leading edge and at the median position in the gap. Taylor series expressions have been obtained which give the exit position, the square of the exit velocity, and the tangent of the angle of deflection in the field. The existence, uniqueness, continuity, and uniform convergence of these series solutions are established. The equation of the family of straight lines which the ions follow beyond the electrostatic field and before the magnetic field are obtained. The existence, location, and width of a virtual source are established for this system under the above conditions of collimation. Expressions for the coordinates of the faces of the magnetic pole pieces are obtained for the case where the leading and trailing faces are mirror images of one another, in the line containing the centers of curvature of the paths of the ions in the magnetic field. The maximum mass-resolution is obtained for a magnetic deflection of about one radian when the electric deflection is one fourth of a radian. A study is made of the corrections for various edge effects in the magnetic field. Tables are given of the numerical results of this investigation.

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