Mass spectrometer and ion source

Abstract

An ion beam having a good converging property and a good quality is provided by satisfying the limitations controlling both angle of dispersion and the width of beam at the same time. The voltage 12d of a repeller electrode 1f in an ion source of electron bombardment type is input to an ion source state monitor 11 and the ion source state monitor 11 output a predicted value 12e of the voltage applied to an extractor electrode 1g to an extractor power source 9. As for the extractor electrode system, the width of a slit in the acceleration electrode 1b is made larger than the width of a slit of the extractor electrode 1g, and the extractor electrode 1g is set in a position apart from the acceleration electrode 1b by the distance nearly equal to the distance between the acceleration electrode 1b and the ion generating region 2a. By doing so, the electric field leaked from the slit of the acceleration electrode 1b to the inside of the ionization chamber 1a expands to the vicinity of the ion generating region. As the result, the ion beam 2 is effectively extracted to pass through the slits in the acceleration electrode 1b and the extractor 1g. The amount of the current passing through the slits is measured with an ion current monitor 8a and the voltage 12f of a converging electrode 1d is adjusted so that the value of the current becomes the maximum.