Modelling Ion Production inside an Electron Impact Ionizer for High-Vacuum Gas Analysis

Residual Gas Analyzers (RGA) are often used to measure background gases and contaminations in vacuum systems. An ionizer is used to ionize gas molecules and these ions are accelerated and focused by an electrical field from the ion source to form an ion beam. The ions can be discriminated based on mass/charge ratio by a magnetic field, and the selected ions are captured by a detector. The ion charge flux at this detector is measured as a current. TNO is developing a new kind of contamination analyzer for high-vacuum systems for real time detection of contaminants. We rely on commercial available electron impact ion sources to generate the ions. To study the resulting ion beam as a function of partial gas pressure, gas composition, emission current, and source dimensions we developed a 3D COMSOL 5.5 model using the Electrostatics (es) and Charged Particle Tracing (cpt) modules. The main parameters to be studied are the ion energy distribution and the ion production rate. For our system we require a very homogeneous ion energy and maximized ion production for the detection of contaminants at high-vacuum regimes.