DOUBLE-FOCUSSING MASS SPECTROMETERS

摘要

There is disclosed a spectrometer having an electrostatic analyser and a magnet producing a radial electrostatic field and a homogeneous magnetic field respectively, so arranged in tandem that an ion optical beam passing through them is normal to the entry and exit boundaries of the electrostatic field and to the inner face of the magnetic field adjacent to the analyser, but non-normal to the outer face of the magnetic field. The deflection of the ion-optical beam in the electrostatic and magnetic fields being in the same sense, characterized in that the parameters thereof are related by specific equations as a result of which the five aberration coefficients B1, B2, B11, B12 and B22 can all be simultaneously zero. Some of the more important parameters for the equations are: 1) the angle of deflection of the beam in the magnetic field; 2) the ratio of the radius of curvature of the mean beam axis in the electrostatic field to the radius of curvature of the mean beam axis in the magnetic field; and 3) the ratio of distance from the outer face of the magnetic field to the aberration-free focal point when the beam passes first through the electrostatic analyser, to the radius of curvature of the mean beam axis in the magnetic field.