Selective ion source for high intensity focused and collimated ion beams - coupling with high resolution cycloidal path sector

摘要

A mass spectrometer is described in which the ions are submitted to the action of a uniform adjustable electrical field {right arrow over (E1, within a set of plane parallel electrodes a1, . . . , ai, . . . an fitted with properly located slits for the ions transmission, and to the action of a uniform magnetic induction {right arrow over (B1. A reference system x,y is considered in a plane perpendicular to {right arrow over (B1, the axis x and y being respectively perpendicular and parallel to {right arrow over (E1, and the origin of the reference system being fixed at an average starting point of the ions. The crossed fields {right arrow over (E1,{right arrow over (B1, act together in an area where yd, d being a distance separating the average starting point of the ions from the electrode alphan. The selection slit S1 is located at coordinates x=2.1d and y=2d, and the value of E1 that is applied for the selection of the ions having the number of mass n is defined by 1 $E_1=\frac{2itd}{n}it\frac{e}{m}it{B}_1^2,$ with 2 $\frac{e}{m}$ with e/m corresponding to a ratio charge/mass for H+. The ions are created by electronic bombardment only in the vicinity of a plane parallel to {right arrow over (B1, making an angle of 45° with {right arrow over (E1, and a heated filament F for emitting electrons being stretched above the electrodes a1,a2, such that a resulting selected ion beam is parallel to the x axis when crossing S1. The ion beam may feed, under optimal conditions, a "cycloid path" mass spectrometer or a 90° magnetic sector. The system provides improved sensitivity and a high resolution within a small and very simple instrument.