A filament current regulator for solid source mass spectrometers

Abstract

A triple filament ion source has been used to study the temperature dependence of alkali ion emission. The side filaments serve merely as sample holders and are not electrically heated. Neutral particles, volatilized by radiation from the hot centre filament, are ionized on impact with the hot metal surface. The ion beam intensity can be conveniently related to the ionizing filament current by a simple power law whose exponent varies for different alkali compounds. With some samples, the exponent may be as high as 100. In this circumstance, ion beam emission stability of 01% necessitates that the ionizing filament current must be stable to 10 p.p.m. A circuit is presented for a simple, economical filament current regulator whose stability to load variations exceeds this requirement.